Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

15 files changed, 9480 insertions, 0 deletions

diff --git a/drivers/platform/surface/aggregator/Kconfig b/drivers/platform/surface/aggregator/Kconfig
new file mode 100644
index 000000000..c114f9dd5
--- /dev/null
+++ b/drivers/platform/surface/aggregator/Kconfig
@@ -0,0 +1,69 @@
+# SPDX-License-Identifier: GPL-2.0+
+# Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+
+menuconfig SURFACE_AGGREGATOR
+	tristate "Microsoft Surface System Aggregator Module Subsystem and Drivers"
+	depends on SERIAL_DEV_BUS
+	depends on ACPI
+	select CRC_CCITT
+	help
+	  The Surface System Aggregator Module (Surface SAM or SSAM) is an
+	  embedded controller (EC) found on 5th- and later-generation Microsoft
+	  Surface devices (i.e. Surface Pro 5, Surface Book 2, Surface Laptop,
+	  and newer, with exception of Surface Go series devices).
+
+	  Depending on the device in question, this EC provides varying
+	  functionality, including:
+	  - EC access from ACPI via Surface ACPI Notify (5th- and 6th-generation)
+	  - battery status information (all devices)
+	  - thermal sensor access (all devices)
+	  - performance mode / cooling mode control (all devices)
+	  - clipboard detachment system control (Surface Book 2 and 3)
+	  - HID / keyboard input (Surface Laptops, Surface Book 3)
+
+	  This option controls whether the Surface SAM subsystem core will be
+	  built. This includes a driver for the Surface Serial Hub (SSH), which
+	  is the device responsible for the communication with the EC, and a
+	  basic kernel interface exposing the EC functionality to other client
+	  drivers, i.e. allowing them to make requests to the EC and receive
+	  events from it. Selecting this option alone will not provide any
+	  client drivers and therefore no functionality beyond the in-kernel
+	  interface. Said functionality is the responsibility of the respective
+	  client drivers.
+
+	  Note: While 4th-generation Surface devices also make use of a SAM EC,
+	  due to a difference in the communication interface of the controller,
+	  only 5th and later generations are currently supported. Specifically,
+	  devices using SAM-over-SSH are supported, whereas devices using
+	  SAM-over-HID, which is used on the 4th generation, are currently not
+	  supported.
+
+	  Choose m if you want to build the SAM subsystem core and SSH driver as
+	  module, y if you want to build it into the kernel and n if you don't
+	  want it at all.
+
+config SURFACE_AGGREGATOR_BUS
+	bool "Surface System Aggregator Module Bus"
+	depends on SURFACE_AGGREGATOR
+	default y
+	help
+	  Expands the Surface System Aggregator Module (SSAM) core driver by
+	  providing a dedicated bus and client-device type.
+
+	  This bus and device type are intended to provide and simplify support
+	  for non-platform and non-ACPI SSAM devices, i.e. SSAM devices that are
+	  not auto-detectable via the conventional means (e.g. ACPI).
+
+config SURFACE_AGGREGATOR_ERROR_INJECTION
+	bool "Surface System Aggregator Module Error Injection Capabilities"
+	depends on SURFACE_AGGREGATOR
+	depends on FUNCTION_ERROR_INJECTION
+	help
+	  Provides error-injection capabilities for the Surface System
+	  Aggregator Module subsystem and Surface Serial Hub driver.
+
+	  Specifically, exports error injection hooks to be used with the
+	  kernel's function error injection capabilities to simulate underlying
+	  transport and communication problems, such as invalid data sent to or
+	  received from the EC, dropped data, and communication timeouts.
+	  Intended for development and debugging.
diff --git a/drivers/platform/surface/aggregator/Makefile b/drivers/platform/surface/aggregator/Makefile
new file mode 100644
index 000000000..fdf664a21
--- /dev/null
+++ b/drivers/platform/surface/aggregator/Makefile
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0+
+# Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+
+# For include/trace/define_trace.h to include trace.h
+CFLAGS_core.o = -I$(src)
+
+obj-$(CONFIG_SURFACE_AGGREGATOR) += surface_aggregator.o
+
+surface_aggregator-y := core.o
+surface_aggregator-y += ssh_parser.o
+surface_aggregator-y += ssh_packet_layer.o
+surface_aggregator-y += ssh_request_layer.o
+surface_aggregator-$(CONFIG_SURFACE_AGGREGATOR_BUS) += bus.o
+surface_aggregator-y += controller.o
diff --git a/drivers/platform/surface/aggregator/bus.c b/drivers/platform/surface/aggregator/bus.c
new file mode 100644
index 000000000..b501a79f2
--- /dev/null
+++ b/drivers/platform/surface/aggregator/bus.c
@@ -0,0 +1,524 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Surface System Aggregator Module bus and device integration.
+ *
+ * Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#include <linux/device.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+
+#include <linux/surface_aggregator/controller.h>
+#include <linux/surface_aggregator/device.h>
+
+#include "bus.h"
+#include "controller.h"
+
+
+/* -- Device and bus functions. --------------------------------------------- */
+
+static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
+			     char *buf)
+{
+	struct ssam_device *sdev = to_ssam_device(dev);
+
+	return sysfs_emit(buf, "ssam:d%02Xc%02Xt%02Xi%02Xf%02X\n",
+			sdev->uid.domain, sdev->uid.category, sdev->uid.target,
+			sdev->uid.instance, sdev->uid.function);
+}
+static DEVICE_ATTR_RO(modalias);
+
+static struct attribute *ssam_device_attrs[] = {
+	&dev_attr_modalias.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(ssam_device);
+
+static int ssam_device_uevent(struct device *dev, struct kobj_uevent_env *env)
+{
+	struct ssam_device *sdev = to_ssam_device(dev);
+
+	return add_uevent_var(env, "MODALIAS=ssam:d%02Xc%02Xt%02Xi%02Xf%02X",
+			      sdev->uid.domain, sdev->uid.category,
+			      sdev->uid.target, sdev->uid.instance,
+			      sdev->uid.function);
+}
+
+static void ssam_device_release(struct device *dev)
+{
+	struct ssam_device *sdev = to_ssam_device(dev);
+
+	ssam_controller_put(sdev->ctrl);
+	fwnode_handle_put(sdev->dev.fwnode);
+	kfree(sdev);
+}
+
+const struct device_type ssam_device_type = {
+	.name    = "surface_aggregator_device",
+	.groups  = ssam_device_groups,
+	.uevent  = ssam_device_uevent,
+	.release = ssam_device_release,
+};
+EXPORT_SYMBOL_GPL(ssam_device_type);
+
+/**
+ * ssam_device_alloc() - Allocate and initialize a SSAM client device.
+ * @ctrl: The controller under which the device should be added.
+ * @uid:  The UID of the device to be added.
+ *
+ * Allocates and initializes a new client device. The parent of the device
+ * will be set to the controller device and the name will be set based on the
+ * UID. Note that the device still has to be added via ssam_device_add().
+ * Refer to that function for more details.
+ *
+ * Return: Returns the newly allocated and initialized SSAM client device, or
+ * %NULL if it could not be allocated.
+ */
+struct ssam_device *ssam_device_alloc(struct ssam_controller *ctrl,
+				      struct ssam_device_uid uid)
+{
+	struct ssam_device *sdev;
+
+	sdev = kzalloc(sizeof(*sdev), GFP_KERNEL);
+	if (!sdev)
+		return NULL;
+
+	device_initialize(&sdev->dev);
+	sdev->dev.bus = &ssam_bus_type;
+	sdev->dev.type = &ssam_device_type;
+	sdev->dev.parent = ssam_controller_device(ctrl);
+	sdev->ctrl = ssam_controller_get(ctrl);
+	sdev->uid = uid;
+
+	dev_set_name(&sdev->dev, "%02x:%02x:%02x:%02x:%02x",
+		     sdev->uid.domain, sdev->uid.category, sdev->uid.target,
+		     sdev->uid.instance, sdev->uid.function);
+
+	return sdev;
+}
+EXPORT_SYMBOL_GPL(ssam_device_alloc);
+
+/**
+ * ssam_device_add() - Add a SSAM client device.
+ * @sdev: The SSAM client device to be added.
+ *
+ * Added client devices must be guaranteed to always have a valid and active
+ * controller. Thus, this function will fail with %-ENODEV if the controller
+ * of the device has not been initialized yet, has been suspended, or has been
+ * shut down.
+ *
+ * The caller of this function should ensure that the corresponding call to
+ * ssam_device_remove() is issued before the controller is shut down. If the
+ * added device is a direct child of the controller device (default), it will
+ * be automatically removed when the controller is shut down.
+ *
+ * By default, the controller device will become the parent of the newly
+ * created client device. The parent may be changed before ssam_device_add is
+ * called, but care must be taken that a) the correct suspend/resume ordering
+ * is guaranteed and b) the client device does not outlive the controller,
+ * i.e. that the device is removed before the controller is being shut down.
+ * In case these guarantees have to be manually enforced, please refer to the
+ * ssam_client_link() and ssam_client_bind() functions, which are intended to
+ * set up device-links for this purpose.
+ *
+ * Return: Returns zero on success, a negative error code on failure.
+ */
+int ssam_device_add(struct ssam_device *sdev)
+{
+	int status;
+
+	/*
+	 * Ensure that we can only add new devices to a controller if it has
+	 * been started and is not going away soon. This works in combination
+	 * with ssam_controller_remove_clients to ensure driver presence for the
+	 * controller device, i.e. it ensures that the controller (sdev->ctrl)
+	 * is always valid and can be used for requests as long as the client
+	 * device we add here is registered as child under it. This essentially
+	 * guarantees that the client driver can always expect the preconditions
+	 * for functions like ssam_request_sync (controller has to be started
+	 * and is not suspended) to hold and thus does not have to check for
+	 * them.
+	 *
+	 * Note that for this to work, the controller has to be a parent device.
+	 * If it is not a direct parent, care has to be taken that the device is
+	 * removed via ssam_device_remove(), as device_unregister does not
+	 * remove child devices recursively.
+	 */
+	ssam_controller_statelock(sdev->ctrl);
+
+	if (sdev->ctrl->state != SSAM_CONTROLLER_STARTED) {
+		ssam_controller_stateunlock(sdev->ctrl);
+		return -ENODEV;
+	}
+
+	status = device_add(&sdev->dev);
+
+	ssam_controller_stateunlock(sdev->ctrl);
+	return status;
+}
+EXPORT_SYMBOL_GPL(ssam_device_add);
+
+/**
+ * ssam_device_remove() - Remove a SSAM client device.
+ * @sdev: The device to remove.
+ *
+ * Removes and unregisters the provided SSAM client device.
+ */
+void ssam_device_remove(struct ssam_device *sdev)
+{
+	device_unregister(&sdev->dev);
+}
+EXPORT_SYMBOL_GPL(ssam_device_remove);
+
+/**
+ * ssam_device_id_compatible() - Check if a device ID matches a UID.
+ * @id:  The device ID as potential match.
+ * @uid: The device UID matching against.
+ *
+ * Check if the given ID is a match for the given UID, i.e. if a device with
+ * the provided UID is compatible to the given ID following the match rules
+ * described in its &ssam_device_id.match_flags member.
+ *
+ * Return: Returns %true if the given UID is compatible to the match rule
+ * described by the given ID, %false otherwise.
+ */
+static bool ssam_device_id_compatible(const struct ssam_device_id *id,
+				      struct ssam_device_uid uid)
+{
+	if (id->domain != uid.domain || id->category != uid.category)
+		return false;
+
+	if ((id->match_flags & SSAM_MATCH_TARGET) && id->target != uid.target)
+		return false;
+
+	if ((id->match_flags & SSAM_MATCH_INSTANCE) && id->instance != uid.instance)
+		return false;
+
+	if ((id->match_flags & SSAM_MATCH_FUNCTION) && id->function != uid.function)
+		return false;
+
+	return true;
+}
+
+/**
+ * ssam_device_id_is_null() - Check if a device ID is null.
+ * @id: The device ID to check.
+ *
+ * Check if a given device ID is null, i.e. all zeros. Used to check for the
+ * end of ``MODULE_DEVICE_TABLE(ssam, ...)`` or similar lists.
+ *
+ * Return: Returns %true if the given ID represents a null ID, %false
+ * otherwise.
+ */
+static bool ssam_device_id_is_null(const struct ssam_device_id *id)
+{
+	return id->match_flags == 0 &&
+		id->domain == 0 &&
+		id->category == 0 &&
+		id->target == 0 &&
+		id->instance == 0 &&
+		id->function == 0 &&
+		id->driver_data == 0;
+}
+
+/**
+ * ssam_device_id_match() - Find the matching ID table entry for the given UID.
+ * @table: The table to search in.
+ * @uid:   The UID to matched against the individual table entries.
+ *
+ * Find the first match for the provided device UID in the provided ID table
+ * and return it. Returns %NULL if no match could be found.
+ */
+const struct ssam_device_id *ssam_device_id_match(const struct ssam_device_id *table,
+						  const struct ssam_device_uid uid)
+{
+	const struct ssam_device_id *id;
+
+	for (id = table; !ssam_device_id_is_null(id); ++id)
+		if (ssam_device_id_compatible(id, uid))
+			return id;
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(ssam_device_id_match);
+
+/**
+ * ssam_device_get_match() - Find and return the ID matching the device in the
+ * ID table of the bound driver.
+ * @dev: The device for which to get the matching ID table entry.
+ *
+ * Find the fist match for the UID of the device in the ID table of the
+ * currently bound driver and return it. Returns %NULL if the device does not
+ * have a driver bound to it, the driver does not have match_table (i.e. it is
+ * %NULL), or there is no match in the driver's match_table.
+ *
+ * This function essentially calls ssam_device_id_match() with the ID table of
+ * the bound device driver and the UID of the device.
+ *
+ * Return: Returns the first match for the UID of the device in the device
+ * driver's match table, or %NULL if no such match could be found.
+ */
+const struct ssam_device_id *ssam_device_get_match(const struct ssam_device *dev)
+{
+	const struct ssam_device_driver *sdrv;
+
+	sdrv = to_ssam_device_driver(dev->dev.driver);
+	if (!sdrv)
+		return NULL;
+
+	if (!sdrv->match_table)
+		return NULL;
+
+	return ssam_device_id_match(sdrv->match_table, dev->uid);
+}
+EXPORT_SYMBOL_GPL(ssam_device_get_match);
+
+/**
+ * ssam_device_get_match_data() - Find the ID matching the device in the
+ * ID table of the bound driver and return its ``driver_data`` member.
+ * @dev: The device for which to get the match data.
+ *
+ * Find the fist match for the UID of the device in the ID table of the
+ * corresponding driver and return its driver_data. Returns %NULL if the
+ * device does not have a driver bound to it, the driver does not have
+ * match_table (i.e. it is %NULL), there is no match in the driver's
+ * match_table, or the match does not have any driver_data.
+ *
+ * This function essentially calls ssam_device_get_match() and, if any match
+ * could be found, returns its ``struct ssam_device_id.driver_data`` member.
+ *
+ * Return: Returns the driver data associated with the first match for the UID
+ * of the device in the device driver's match table, or %NULL if no such match
+ * could be found.
+ */
+const void *ssam_device_get_match_data(const struct ssam_device *dev)
+{
+	const struct ssam_device_id *id;
+
+	id = ssam_device_get_match(dev);
+	if (!id)
+		return NULL;
+
+	return (const void *)id->driver_data;
+}
+EXPORT_SYMBOL_GPL(ssam_device_get_match_data);
+
+static int ssam_bus_match(struct device *dev, struct device_driver *drv)
+{
+	struct ssam_device_driver *sdrv = to_ssam_device_driver(drv);
+	struct ssam_device *sdev = to_ssam_device(dev);
+
+	if (!is_ssam_device(dev))
+		return 0;
+
+	return !!ssam_device_id_match(sdrv->match_table, sdev->uid);
+}
+
+static int ssam_bus_probe(struct device *dev)
+{
+	return to_ssam_device_driver(dev->driver)
+		->probe(to_ssam_device(dev));
+}
+
+static void ssam_bus_remove(struct device *dev)
+{
+	struct ssam_device_driver *sdrv = to_ssam_device_driver(dev->driver);
+
+	if (sdrv->remove)
+		sdrv->remove(to_ssam_device(dev));
+}
+
+struct bus_type ssam_bus_type = {
+	.name   = "surface_aggregator",
+	.match  = ssam_bus_match,
+	.probe  = ssam_bus_probe,
+	.remove = ssam_bus_remove,
+};
+EXPORT_SYMBOL_GPL(ssam_bus_type);
+
+/**
+ * __ssam_device_driver_register() - Register a SSAM client device driver.
+ * @sdrv:  The driver to register.
+ * @owner: The module owning the provided driver.
+ *
+ * Please refer to the ssam_device_driver_register() macro for the normal way
+ * to register a driver from inside its owning module.
+ */
+int __ssam_device_driver_register(struct ssam_device_driver *sdrv,
+				  struct module *owner)
+{
+	sdrv->driver.owner = owner;
+	sdrv->driver.bus = &ssam_bus_type;
+
+	/* force drivers to async probe so I/O is possible in probe */
+	sdrv->driver.probe_type = PROBE_PREFER_ASYNCHRONOUS;
+
+	return driver_register(&sdrv->driver);
+}
+EXPORT_SYMBOL_GPL(__ssam_device_driver_register);
+
+/**
+ * ssam_device_driver_unregister - Unregister a SSAM device driver.
+ * @sdrv: The driver to unregister.
+ */
+void ssam_device_driver_unregister(struct ssam_device_driver *sdrv)
+{
+	driver_unregister(&sdrv->driver);
+}
+EXPORT_SYMBOL_GPL(ssam_device_driver_unregister);
+
+
+/* -- Bus registration. ----------------------------------------------------- */
+
+/**
+ * ssam_bus_register() - Register and set-up the SSAM client device bus.
+ */
+int ssam_bus_register(void)
+{
+	return bus_register(&ssam_bus_type);
+}
+
+/**
+ * ssam_bus_unregister() - Unregister the SSAM client device bus.
+ */
+void ssam_bus_unregister(void)
+{
+	return bus_unregister(&ssam_bus_type);
+}
+
+
+/* -- Helpers for controller and hub devices. ------------------------------- */
+
+static int ssam_device_uid_from_string(const char *str, struct ssam_device_uid *uid)
+{
+	u8 d, tc, tid, iid, fn;
+	int n;
+
+	n = sscanf(str, "%hhx:%hhx:%hhx:%hhx:%hhx", &d, &tc, &tid, &iid, &fn);
+	if (n != 5)
+		return -EINVAL;
+
+	uid->domain = d;
+	uid->category = tc;
+	uid->target = tid;
+	uid->instance = iid;
+	uid->function = fn;
+
+	return 0;
+}
+
+static int ssam_get_uid_for_node(struct fwnode_handle *node, struct ssam_device_uid *uid)
+{
+	const char *str = fwnode_get_name(node);
+
+	/*
+	 * To simplify definitions of firmware nodes, we set the device name
+	 * based on the UID of the device, prefixed with "ssam:".
+	 */
+	if (strncmp(str, "ssam:", strlen("ssam:")) != 0)
+		return -ENODEV;
+
+	str += strlen("ssam:");
+	return ssam_device_uid_from_string(str, uid);
+}
+
+static int ssam_add_client_device(struct device *parent, struct ssam_controller *ctrl,
+				  struct fwnode_handle *node)
+{
+	struct ssam_device_uid uid;
+	struct ssam_device *sdev;
+	int status;
+
+	status = ssam_get_uid_for_node(node, &uid);
+	if (status)
+		return status;
+
+	sdev = ssam_device_alloc(ctrl, uid);
+	if (!sdev)
+		return -ENOMEM;
+
+	sdev->dev.parent = parent;
+	sdev->dev.fwnode = fwnode_handle_get(node);
+
+	status = ssam_device_add(sdev);
+	if (status)
+		ssam_device_put(sdev);
+
+	return status;
+}
+
+/**
+ * __ssam_register_clients() - Register client devices defined under the
+ * given firmware node as children of the given device.
+ * @parent: The parent device under which clients should be registered.
+ * @ctrl: The controller with which client should be registered.
+ * @node: The firmware node holding definitions of the devices to be added.
+ *
+ * Register all clients that have been defined as children of the given root
+ * firmware node as children of the given parent device. The respective child
+ * firmware nodes will be associated with the correspondingly created child
+ * devices.
+ *
+ * The given controller will be used to instantiate the new devices. See
+ * ssam_device_add() for details.
+ *
+ * Note that, generally, the use of either ssam_device_register_clients() or
+ * ssam_register_clients() should be preferred as they directly use the
+ * firmware node and/or controller associated with the given device. This
+ * function is only intended for use when different device specifications (e.g.
+ * ACPI and firmware nodes) need to be combined (as is done in the platform hub
+ * of the device registry).
+ *
+ * Return: Returns zero on success, nonzero on failure.
+ */
+int __ssam_register_clients(struct device *parent, struct ssam_controller *ctrl,
+			    struct fwnode_handle *node)
+{
+	struct fwnode_handle *child;
+	int status;
+
+	fwnode_for_each_child_node(node, child) {
+		/*
+		 * Try to add the device specified in the firmware node. If
+		 * this fails with -ENODEV, the node does not specify any SSAM
+		 * device, so ignore it and continue with the next one.
+		 */
+		status = ssam_add_client_device(parent, ctrl, child);
+		if (status && status != -ENODEV) {
+			fwnode_handle_put(child);
+			goto err;
+		}
+	}
+
+	return 0;
+err:
+	ssam_remove_clients(parent);
+	return status;
+}
+EXPORT_SYMBOL_GPL(__ssam_register_clients);
+
+static int ssam_remove_device(struct device *dev, void *_data)
+{
+	struct ssam_device *sdev = to_ssam_device(dev);
+
+	if (is_ssam_device(dev))
+		ssam_device_remove(sdev);
+
+	return 0;
+}
+
+/**
+ * ssam_remove_clients() - Remove SSAM client devices registered as direct
+ * children under the given parent device.
+ * @dev: The (parent) device to remove all direct clients for.
+ *
+ * Remove all SSAM client devices registered as direct children under the given
+ * device. Note that this only accounts for direct children of the device.
+ * Refer to ssam_device_add()/ssam_device_remove() for more details.
+ */
+void ssam_remove_clients(struct device *dev)
+{
+	device_for_each_child_reverse(dev, NULL, ssam_remove_device);
+}
+EXPORT_SYMBOL_GPL(ssam_remove_clients);
diff --git a/drivers/platform/surface/aggregator/bus.h b/drivers/platform/surface/aggregator/bus.h
new file mode 100644
index 000000000..5b4dbf219
--- /dev/null
+++ b/drivers/platform/surface/aggregator/bus.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Surface System Aggregator Module bus and device integration.
+ *
+ * Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#ifndef _SURFACE_AGGREGATOR_BUS_H
+#define _SURFACE_AGGREGATOR_BUS_H
+
+#include <linux/surface_aggregator/controller.h>
+
+#ifdef CONFIG_SURFACE_AGGREGATOR_BUS
+
+int ssam_bus_register(void);
+void ssam_bus_unregister(void);
+
+#else /* CONFIG_SURFACE_AGGREGATOR_BUS */
+
+static inline int ssam_bus_register(void) { return 0; }
+static inline void ssam_bus_unregister(void) {}
+
+#endif /* CONFIG_SURFACE_AGGREGATOR_BUS */
+#endif /* _SURFACE_AGGREGATOR_BUS_H */
diff --git a/drivers/platform/surface/aggregator/controller.c b/drivers/platform/surface/aggregator/controller.c
new file mode 100644
index 000000000..30cea324f
--- /dev/null
+++ b/drivers/platform/surface/aggregator/controller.c
@@ -0,0 +1,2807 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Main SSAM/SSH controller structure and functionality.
+ *
+ * Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#include <linux/acpi.h>
+#include <linux/atomic.h>
+#include <linux/completion.h>
+#include <linux/gpio/consumer.h>
+#include <linux/interrupt.h>
+#include <linux/kref.h>
+#include <linux/limits.h>
+#include <linux/list.h>
+#include <linux/lockdep.h>
+#include <linux/mutex.h>
+#include <linux/rculist.h>
+#include <linux/rbtree.h>
+#include <linux/rwsem.h>
+#include <linux/serdev.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/srcu.h>
+#include <linux/types.h>
+#include <linux/workqueue.h>
+
+#include <linux/surface_aggregator/controller.h>
+#include <linux/surface_aggregator/serial_hub.h>
+
+#include "controller.h"
+#include "ssh_msgb.h"
+#include "ssh_request_layer.h"
+
+#include "trace.h"
+
+
+/* -- Safe counters. -------------------------------------------------------- */
+
+/**
+ * ssh_seq_reset() - Reset/initialize sequence ID counter.
+ * @c: The counter to reset.
+ */
+static void ssh_seq_reset(struct ssh_seq_counter *c)
+{
+	WRITE_ONCE(c->value, 0);
+}
+
+/**
+ * ssh_seq_next() - Get next sequence ID.
+ * @c: The counter providing the sequence IDs.
+ *
+ * Return: Returns the next sequence ID of the counter.
+ */
+static u8 ssh_seq_next(struct ssh_seq_counter *c)
+{
+	u8 old = READ_ONCE(c->value);
+	u8 new = old + 1;
+	u8 ret;
+
+	while (unlikely((ret = cmpxchg(&c->value, old, new)) != old)) {
+		old = ret;
+		new = old + 1;
+	}
+
+	return old;
+}
+
+/**
+ * ssh_rqid_reset() - Reset/initialize request ID counter.
+ * @c: The counter to reset.
+ */
+static void ssh_rqid_reset(struct ssh_rqid_counter *c)
+{
+	WRITE_ONCE(c->value, 0);
+}
+
+/**
+ * ssh_rqid_next() - Get next request ID.
+ * @c: The counter providing the request IDs.
+ *
+ * Return: Returns the next request ID of the counter, skipping any reserved
+ * request IDs.
+ */
+static u16 ssh_rqid_next(struct ssh_rqid_counter *c)
+{
+	u16 old = READ_ONCE(c->value);
+	u16 new = ssh_rqid_next_valid(old);
+	u16 ret;
+
+	while (unlikely((ret = cmpxchg(&c->value, old, new)) != old)) {
+		old = ret;
+		new = ssh_rqid_next_valid(old);
+	}
+
+	return old;
+}
+
+
+/* -- Event notifier/callbacks. --------------------------------------------- */
+/*
+ * The notifier system is based on linux/notifier.h, specifically the SRCU
+ * implementation. The difference to that is, that some bits of the notifier
+ * call return value can be tracked across multiple calls. This is done so
+ * that handling of events can be tracked and a warning can be issued in case
+ * an event goes unhandled. The idea of that warning is that it should help
+ * discover and identify new/currently unimplemented features.
+ */
+
+/**
+ * ssam_event_matches_notifier() - Test if an event matches a notifier.
+ * @n: The event notifier to test against.
+ * @event: The event to test.
+ *
+ * Return: Returns %true if the given event matches the given notifier
+ * according to the rules set in the notifier's event mask, %false otherwise.
+ */
+static bool ssam_event_matches_notifier(const struct ssam_event_notifier *n,
+					const struct ssam_event *event)
+{
+	bool match = n->event.id.target_category == event->target_category;
+
+	if (n->event.mask & SSAM_EVENT_MASK_TARGET)
+		match &= n->event.reg.target_id == event->target_id;
+
+	if (n->event.mask & SSAM_EVENT_MASK_INSTANCE)
+		match &= n->event.id.instance == event->instance_id;
+
+	return match;
+}
+
+/**
+ * ssam_nfblk_call_chain() - Call event notifier callbacks of the given chain.
+ * @nh:    The notifier head for which the notifier callbacks should be called.
+ * @event: The event data provided to the callbacks.
+ *
+ * Call all registered notifier callbacks in order of their priority until
+ * either no notifier is left or a notifier returns a value with the
+ * %SSAM_NOTIF_STOP bit set. Note that this bit is automatically set via
+ * ssam_notifier_from_errno() on any non-zero error value.
+ *
+ * Return: Returns the notifier status value, which contains the notifier
+ * status bits (%SSAM_NOTIF_HANDLED and %SSAM_NOTIF_STOP) as well as a
+ * potential error value returned from the last executed notifier callback.
+ * Use ssam_notifier_to_errno() to convert this value to the original error
+ * value.
+ */
+static int ssam_nfblk_call_chain(struct ssam_nf_head *nh, struct ssam_event *event)
+{
+	struct ssam_event_notifier *nf;
+	int ret = 0, idx;
+
+	idx = srcu_read_lock(&nh->srcu);
+
+	list_for_each_entry_rcu(nf, &nh->head, base.node,
+				srcu_read_lock_held(&nh->srcu)) {
+		if (ssam_event_matches_notifier(nf, event)) {
+			ret = (ret & SSAM_NOTIF_STATE_MASK) | nf->base.fn(nf, event);
+			if (ret & SSAM_NOTIF_STOP)
+				break;
+		}
+	}
+
+	srcu_read_unlock(&nh->srcu, idx);
+	return ret;
+}
+
+/**
+ * ssam_nfblk_insert() - Insert a new notifier block into the given notifier
+ * list.
+ * @nh: The notifier head into which the block should be inserted.
+ * @nb: The notifier block to add.
+ *
+ * Note: This function must be synchronized by the caller with respect to other
+ * insert, find, and/or remove calls by holding ``struct ssam_nf.lock``.
+ *
+ * Return: Returns zero on success, %-EEXIST if the notifier block has already
+ * been registered.
+ */
+static int ssam_nfblk_insert(struct ssam_nf_head *nh, struct ssam_notifier_block *nb)
+{
+	struct ssam_notifier_block *p;
+	struct list_head *h;
+
+	/* Runs under lock, no need for RCU variant. */
+	list_for_each(h, &nh->head) {
+		p = list_entry(h, struct ssam_notifier_block, node);
+
+		if (unlikely(p == nb)) {
+			WARN(1, "double register detected");
+			return -EEXIST;
+		}
+
+		if (nb->priority > p->priority)
+			break;
+	}
+
+	list_add_tail_rcu(&nb->node, h);
+	return 0;
+}
+
+/**
+ * ssam_nfblk_find() - Check if a notifier block is registered on the given
+ * notifier head.
+ * list.
+ * @nh: The notifier head on which to search.
+ * @nb: The notifier block to search for.
+ *
+ * Note: This function must be synchronized by the caller with respect to other
+ * insert, find, and/or remove calls by holding ``struct ssam_nf.lock``.
+ *
+ * Return: Returns true if the given notifier block is registered on the given
+ * notifier head, false otherwise.
+ */
+static bool ssam_nfblk_find(struct ssam_nf_head *nh, struct ssam_notifier_block *nb)
+{
+	struct ssam_notifier_block *p;
+
+	/* Runs under lock, no need for RCU variant. */
+	list_for_each_entry(p, &nh->head, node) {
+		if (p == nb)
+			return true;
+	}
+
+	return false;
+}
+
+/**
+ * ssam_nfblk_remove() - Remove a notifier block from its notifier list.
+ * @nb: The notifier block to be removed.
+ *
+ * Note: This function must be synchronized by the caller with respect to
+ * other insert, find, and/or remove calls by holding ``struct ssam_nf.lock``.
+ * Furthermore, the caller _must_ ensure SRCU synchronization by calling
+ * synchronize_srcu() with ``nh->srcu`` after leaving the critical section, to
+ * ensure that the removed notifier block is not in use any more.
+ */
+static void ssam_nfblk_remove(struct ssam_notifier_block *nb)
+{
+	list_del_rcu(&nb->node);
+}
+
+/**
+ * ssam_nf_head_init() - Initialize the given notifier head.
+ * @nh: The notifier head to initialize.
+ */
+static int ssam_nf_head_init(struct ssam_nf_head *nh)
+{
+	int status;
+
+	status = init_srcu_struct(&nh->srcu);
+	if (status)
+		return status;
+
+	INIT_LIST_HEAD(&nh->head);
+	return 0;
+}
+
+/**
+ * ssam_nf_head_destroy() - Deinitialize the given notifier head.
+ * @nh: The notifier head to deinitialize.
+ */
+static void ssam_nf_head_destroy(struct ssam_nf_head *nh)
+{
+	cleanup_srcu_struct(&nh->srcu);
+}
+
+
+/* -- Event/notification registry. ------------------------------------------ */
+
+/**
+ * struct ssam_nf_refcount_key - Key used for event activation reference
+ * counting.
+ * @reg: The registry via which the event is enabled/disabled.
+ * @id:  The ID uniquely describing the event.
+ */
+struct ssam_nf_refcount_key {
+	struct ssam_event_registry reg;
+	struct ssam_event_id id;
+};
+
+/**
+ * struct ssam_nf_refcount_entry - RB-tree entry for reference counting event
+ * activations.
+ * @node:     The node of this entry in the rb-tree.
+ * @key:      The key of the event.
+ * @refcount: The reference-count of the event.
+ * @flags:    The flags used when enabling the event.
+ */
+struct ssam_nf_refcount_entry {
+	struct rb_node node;
+	struct ssam_nf_refcount_key key;
+	int refcount;
+	u8 flags;
+};
+
+/**
+ * ssam_nf_refcount_inc() - Increment reference-/activation-count of the given
+ * event.
+ * @nf:  The notifier system reference.
+ * @reg: The registry used to enable/disable the event.
+ * @id:  The event ID.
+ *
+ * Increments the reference-/activation-count associated with the specified
+ * event type/ID, allocating a new entry for this event ID if necessary. A
+ * newly allocated entry will have a refcount of one.
+ *
+ * Note: ``nf->lock`` must be held when calling this function.
+ *
+ * Return: Returns the refcount entry on success. Returns an error pointer
+ * with %-ENOSPC if there have already been %INT_MAX events of the specified
+ * ID and type registered, or %-ENOMEM if the entry could not be allocated.
+ */
+static struct ssam_nf_refcount_entry *
+ssam_nf_refcount_inc(struct ssam_nf *nf, struct ssam_event_registry reg,
+		     struct ssam_event_id id)
+{
+	struct ssam_nf_refcount_entry *entry;
+	struct ssam_nf_refcount_key key;
+	struct rb_node **link = &nf->refcount.rb_node;
+	struct rb_node *parent = NULL;
+	int cmp;
+
+	lockdep_assert_held(&nf->lock);
+
+	key.reg = reg;
+	key.id = id;
+
+	while (*link) {
+		entry = rb_entry(*link, struct ssam_nf_refcount_entry, node);
+		parent = *link;
+
+		cmp = memcmp(&key, &entry->key, sizeof(key));
+		if (cmp < 0) {
+			link = &(*link)->rb_left;
+		} else if (cmp > 0) {
+			link = &(*link)->rb_right;
+		} else if (entry->refcount < INT_MAX) {
+			entry->refcount++;
+			return entry;
+		} else {
+			WARN_ON(1);
+			return ERR_PTR(-ENOSPC);
+		}
+	}
+
+	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+	if (!entry)
+		return ERR_PTR(-ENOMEM);
+
+	entry->key = key;
+	entry->refcount = 1;
+
+	rb_link_node(&entry->node, parent, link);
+	rb_insert_color(&entry->node, &nf->refcount);
+
+	return entry;
+}
+
+/**
+ * ssam_nf_refcount_dec() - Decrement reference-/activation-count of the given
+ * event.
+ * @nf:  The notifier system reference.
+ * @reg: The registry used to enable/disable the event.
+ * @id:  The event ID.
+ *
+ * Decrements the reference-/activation-count of the specified event,
+ * returning its entry. If the returned entry has a refcount of zero, the
+ * caller is responsible for freeing it using kfree().
+ *
+ * Note: ``nf->lock`` must be held when calling this function.
+ *
+ * Return: Returns the refcount entry on success or %NULL if the entry has not
+ * been found.
+ */
+static struct ssam_nf_refcount_entry *
+ssam_nf_refcount_dec(struct ssam_nf *nf, struct ssam_event_registry reg,
+		     struct ssam_event_id id)
+{
+	struct ssam_nf_refcount_entry *entry;
+	struct ssam_nf_refcount_key key;
+	struct rb_node *node = nf->refcount.rb_node;
+	int cmp;
+
+	lockdep_assert_held(&nf->lock);
+
+	key.reg = reg;
+	key.id = id;
+
+	while (node) {
+		entry = rb_entry(node, struct ssam_nf_refcount_entry, node);
+
+		cmp = memcmp(&key, &entry->key, sizeof(key));
+		if (cmp < 0) {
+			node = node->rb_left;
+		} else if (cmp > 0) {
+			node = node->rb_right;
+		} else {
+			entry->refcount--;
+			if (entry->refcount == 0)
+				rb_erase(&entry->node, &nf->refcount);
+
+			return entry;
+		}
+	}
+
+	return NULL;
+}
+
+/**
+ * ssam_nf_refcount_dec_free() - Decrement reference-/activation-count of the
+ * given event and free its entry if the reference count reaches zero.
+ * @nf:  The notifier system reference.
+ * @reg: The registry used to enable/disable the event.
+ * @id:  The event ID.
+ *
+ * Decrements the reference-/activation-count of the specified event, freeing
+ * its entry if it reaches zero.
+ *
+ * Note: ``nf->lock`` must be held when calling this function.
+ */
+static void ssam_nf_refcount_dec_free(struct ssam_nf *nf,
+				      struct ssam_event_registry reg,
+				      struct ssam_event_id id)
+{
+	struct ssam_nf_refcount_entry *entry;
+
+	lockdep_assert_held(&nf->lock);
+
+	entry = ssam_nf_refcount_dec(nf, reg, id);
+	if (entry && entry->refcount == 0)
+		kfree(entry);
+}
+
+/**
+ * ssam_nf_refcount_empty() - Test if the notification system has any
+ * enabled/active events.
+ * @nf: The notification system.
+ */
+static bool ssam_nf_refcount_empty(struct ssam_nf *nf)
+{
+	return RB_EMPTY_ROOT(&nf->refcount);
+}
+
+/**
+ * ssam_nf_call() - Call notification callbacks for the provided event.
+ * @nf:    The notifier system
+ * @dev:   The associated device, only used for logging.
+ * @rqid:  The request ID of the event.
+ * @event: The event provided to the callbacks.
+ *
+ * Execute registered callbacks in order of their priority until either no
+ * callback is left or a callback returns a value with the %SSAM_NOTIF_STOP
+ * bit set. Note that this bit is set automatically when converting non-zero
+ * error values via ssam_notifier_from_errno() to notifier values.
+ *
+ * Also note that any callback that could handle an event should return a value
+ * with bit %SSAM_NOTIF_HANDLED set, indicating that the event does not go
+ * unhandled/ignored. In case no registered callback could handle an event,
+ * this function will emit a warning.
+ *
+ * In case a callback failed, this function will emit an error message.
+ */
+static void ssam_nf_call(struct ssam_nf *nf, struct device *dev, u16 rqid,
+			 struct ssam_event *event)
+{
+	struct ssam_nf_head *nf_head;
+	int status, nf_ret;
+
+	if (!ssh_rqid_is_event(rqid)) {
+		dev_warn(dev, "event: unsupported rqid: %#06x\n", rqid);
+		return;
+	}
+
+	nf_head = &nf->head[ssh_rqid_to_event(rqid)];
+	nf_ret = ssam_nfblk_call_chain(nf_head, event);
+	status = ssam_notifier_to_errno(nf_ret);
+
+	if (status < 0) {
+		dev_err(dev,
+			"event: error handling event: %d (tc: %#04x, tid: %#04x, cid: %#04x, iid: %#04x)\n",
+			status, event->target_category, event->target_id,
+			event->command_id, event->instance_id);
+	} else if (!(nf_ret & SSAM_NOTIF_HANDLED)) {
+		dev_warn(dev,
+			 "event: unhandled event (rqid: %#04x, tc: %#04x, tid: %#04x, cid: %#04x, iid: %#04x)\n",
+			 rqid, event->target_category, event->target_id,
+			 event->command_id, event->instance_id);
+	}
+}
+
+/**
+ * ssam_nf_init() - Initialize the notifier system.
+ * @nf: The notifier system to initialize.
+ */
+static int ssam_nf_init(struct ssam_nf *nf)
+{
+	int i, status;
+
+	for (i = 0; i < SSH_NUM_EVENTS; i++) {
+		status = ssam_nf_head_init(&nf->head[i]);
+		if (status)
+			break;
+	}
+
+	if (status) {
+		while (i--)
+			ssam_nf_head_destroy(&nf->head[i]);
+
+		return status;
+	}
+
+	mutex_init(&nf->lock);
+	return 0;
+}
+
+/**
+ * ssam_nf_destroy() - Deinitialize the notifier system.
+ * @nf: The notifier system to deinitialize.
+ */
+static void ssam_nf_destroy(struct ssam_nf *nf)
+{
+	int i;
+
+	for (i = 0; i < SSH_NUM_EVENTS; i++)
+		ssam_nf_head_destroy(&nf->head[i]);
+
+	mutex_destroy(&nf->lock);
+}
+
+
+/* -- Event/async request completion system. -------------------------------- */
+
+#define SSAM_CPLT_WQ_NAME	"ssam_cpltq"
+
+/*
+ * SSAM_CPLT_WQ_BATCH - Maximum number of event item completions executed per
+ * work execution. Used to prevent livelocking of the workqueue. Value chosen
+ * via educated guess, may be adjusted.
+ */
+#define SSAM_CPLT_WQ_BATCH	10
+
+/*
+ * SSAM_EVENT_ITEM_CACHE_PAYLOAD_LEN - Maximum payload length for a cached
+ * &struct ssam_event_item.
+ *
+ * This length has been chosen to be accommodate standard touchpad and
+ * keyboard input events. Events with larger payloads will be allocated
+ * separately.
+ */
+#define SSAM_EVENT_ITEM_CACHE_PAYLOAD_LEN	32
+
+static struct kmem_cache *ssam_event_item_cache;
+
+/**
+ * ssam_event_item_cache_init() - Initialize the event item cache.
+ */
+int ssam_event_item_cache_init(void)
+{
+	const unsigned int size = sizeof(struct ssam_event_item)
+				  + SSAM_EVENT_ITEM_CACHE_PAYLOAD_LEN;
+	const unsigned int align = __alignof__(struct ssam_event_item);
+	struct kmem_cache *cache;
+
+	cache = kmem_cache_create("ssam_event_item", size, align, 0, NULL);
+	if (!cache)
+		return -ENOMEM;
+
+	ssam_event_item_cache = cache;
+	return 0;
+}
+
+/**
+ * ssam_event_item_cache_destroy() - Deinitialize the event item cache.
+ */
+void ssam_event_item_cache_destroy(void)
+{
+	kmem_cache_destroy(ssam_event_item_cache);
+	ssam_event_item_cache = NULL;
+}
+
+static void __ssam_event_item_free_cached(struct ssam_event_item *item)
+{
+	kmem_cache_free(ssam_event_item_cache, item);
+}
+
+static void __ssam_event_item_free_generic(struct ssam_event_item *item)
+{
+	kfree(item);
+}
+
+/**
+ * ssam_event_item_free() - Free the provided event item.
+ * @item: The event item to free.
+ */
+static void ssam_event_item_free(struct ssam_event_item *item)
+{
+	trace_ssam_event_item_free(item);
+	item->ops.free(item);
+}
+
+/**
+ * ssam_event_item_alloc() - Allocate an event item with the given payload size.
+ * @len:   The event payload length.
+ * @flags: The flags used for allocation.
+ *
+ * Allocate an event item with the given payload size, preferring allocation
+ * from the event item cache if the payload is small enough (i.e. smaller than
+ * %SSAM_EVENT_ITEM_CACHE_PAYLOAD_LEN). Sets the item operations and payload
+ * length values. The item free callback (``ops.free``) should not be
+ * overwritten after this call.
+ *
+ * Return: Returns the newly allocated event item.
+ */
+static struct ssam_event_item *ssam_event_item_alloc(size_t len, gfp_t flags)
+{
+	struct ssam_event_item *item;
+
+	if (len <= SSAM_EVENT_ITEM_CACHE_PAYLOAD_LEN) {
+		item = kmem_cache_alloc(ssam_event_item_cache, flags);
+		if (!item)
+			return NULL;
+
+		item->ops.free = __ssam_event_item_free_cached;
+	} else {
+		item = kzalloc(struct_size(item, event.data, len), flags);
+		if (!item)
+			return NULL;
+
+		item->ops.free = __ssam_event_item_free_generic;
+	}
+
+	item->event.length = len;
+
+	trace_ssam_event_item_alloc(item, len);
+	return item;
+}
+
+/**
+ * ssam_event_queue_push() - Push an event item to the event queue.
+ * @q:    The event queue.
+ * @item: The item to add.
+ */
+static void ssam_event_queue_push(struct ssam_event_queue *q,
+				  struct ssam_event_item *item)
+{
+	spin_lock(&q->lock);
+	list_add_tail(&item->node, &q->head);
+	spin_unlock(&q->lock);
+}
+
+/**
+ * ssam_event_queue_pop() - Pop the next event item from the event queue.
+ * @q: The event queue.
+ *
+ * Returns and removes the next event item from the queue. Returns %NULL If
+ * there is no event item left.
+ */
+static struct ssam_event_item *ssam_event_queue_pop(struct ssam_event_queue *q)
+{
+	struct ssam_event_item *item;
+
+	spin_lock(&q->lock);
+	item = list_first_entry_or_null(&q->head, struct ssam_event_item, node);
+	if (item)
+		list_del(&item->node);
+	spin_unlock(&q->lock);
+
+	return item;
+}
+
+/**
+ * ssam_event_queue_is_empty() - Check if the event queue is empty.
+ * @q: The event queue.
+ */
+static bool ssam_event_queue_is_empty(struct ssam_event_queue *q)
+{
+	bool empty;
+
+	spin_lock(&q->lock);
+	empty = list_empty(&q->head);
+	spin_unlock(&q->lock);
+
+	return empty;
+}
+
+/**
+ * ssam_cplt_get_event_queue() - Get the event queue for the given parameters.
+ * @cplt: The completion system on which to look for the queue.
+ * @tid:  The target ID of the queue.
+ * @rqid: The request ID representing the event ID for which to get the queue.
+ *
+ * Return: Returns the event queue corresponding to the event type described
+ * by the given parameters. If the request ID does not represent an event,
+ * this function returns %NULL. If the target ID is not supported, this
+ * function will fall back to the default target ID (``tid = 1``).
+ */
+static
+struct ssam_event_queue *ssam_cplt_get_event_queue(struct ssam_cplt *cplt,
+						   u8 tid, u16 rqid)
+{
+	u16 event = ssh_rqid_to_event(rqid);
+	u16 tidx = ssh_tid_to_index(tid);
+
+	if (!ssh_rqid_is_event(rqid)) {
+		dev_err(cplt->dev, "event: unsupported request ID: %#06x\n", rqid);
+		return NULL;
+	}
+
+	if (!ssh_tid_is_valid(tid)) {
+		dev_warn(cplt->dev, "event: unsupported target ID: %u\n", tid);
+		tidx = 0;
+	}
+
+	return &cplt->event.target[tidx].queue[event];
+}
+
+/**
+ * ssam_cplt_submit() - Submit a work item to the completion system workqueue.
+ * @cplt: The completion system.
+ * @work: The work item to submit.
+ */
+static bool ssam_cplt_submit(struct ssam_cplt *cplt, struct work_struct *work)
+{
+	return queue_work(cplt->wq, work);
+}
+
+/**
+ * ssam_cplt_submit_event() - Submit an event to the completion system.
+ * @cplt: The completion system.
+ * @item: The event item to submit.
+ *
+ * Submits the event to the completion system by queuing it on the event item
+ * queue and queuing the respective event queue work item on the completion
+ * workqueue, which will eventually complete the event.
+ *
+ * Return: Returns zero on success, %-EINVAL if there is no event queue that
+ * can handle the given event item.
+ */
+static int ssam_cplt_submit_event(struct ssam_cplt *cplt,
+				  struct ssam_event_item *item)
+{
+	struct ssam_event_queue *evq;
+
+	evq = ssam_cplt_get_event_queue(cplt, item->event.target_id, item->rqid);
+	if (!evq)
+		return -EINVAL;
+
+	ssam_event_queue_push(evq, item);
+	ssam_cplt_submit(cplt, &evq->work);
+	return 0;
+}
+
+/**
+ * ssam_cplt_flush() - Flush the completion system.
+ * @cplt: The completion system.
+ *
+ * Flush the completion system by waiting until all currently submitted work
+ * items have been completed.
+ *
+ * Note: This function does not guarantee that all events will have been
+ * handled once this call terminates. In case of a larger number of
+ * to-be-completed events, the event queue work function may re-schedule its
+ * work item, which this flush operation will ignore.
+ *
+ * This operation is only intended to, during normal operation prior to
+ * shutdown, try to complete most events and requests to get them out of the
+ * system while the system is still fully operational. It does not aim to
+ * provide any guarantee that all of them have been handled.
+ */
+static void ssam_cplt_flush(struct ssam_cplt *cplt)
+{
+	flush_workqueue(cplt->wq);
+}
+
+static void ssam_event_queue_work_fn(struct work_struct *work)
+{
+	struct ssam_event_queue *queue;
+	struct ssam_event_item *item;
+	struct ssam_nf *nf;
+	struct device *dev;
+	unsigned int iterations = SSAM_CPLT_WQ_BATCH;
+
+	queue = container_of(work, struct ssam_event_queue, work);
+	nf = &queue->cplt->event.notif;
+	dev = queue->cplt->dev;
+
+	/* Limit number of processed events to avoid livelocking. */
+	do {
+		item = ssam_event_queue_pop(queue);
+		if (!item)
+			return;
+
+		ssam_nf_call(nf, dev, item->rqid, &item->event);
+		ssam_event_item_free(item);
+	} while (--iterations);
+
+	if (!ssam_event_queue_is_empty(queue))
+		ssam_cplt_submit(queue->cplt, &queue->work);
+}
+
+/**
+ * ssam_event_queue_init() - Initialize an event queue.
+ * @cplt: The completion system on which the queue resides.
+ * @evq:  The event queue to initialize.
+ */
+static void ssam_event_queue_init(struct ssam_cplt *cplt,
+				  struct ssam_event_queue *evq)
+{
+	evq->cplt = cplt;
+	spin_lock_init(&evq->lock);
+	INIT_LIST_HEAD(&evq->head);
+	INIT_WORK(&evq->work, ssam_event_queue_work_fn);
+}
+
+/**
+ * ssam_cplt_init() - Initialize completion system.
+ * @cplt: The completion system to initialize.
+ * @dev:  The device used for logging.
+ */
+static int ssam_cplt_init(struct ssam_cplt *cplt, struct device *dev)
+{
+	struct ssam_event_target *target;
+	int status, c, i;
+
+	cplt->dev = dev;
+
+	cplt->wq = alloc_workqueue(SSAM_CPLT_WQ_NAME, WQ_UNBOUND | WQ_MEM_RECLAIM, 0);
+	if (!cplt->wq)
+		return -ENOMEM;
+
+	for (c = 0; c < ARRAY_SIZE(cplt->event.target); c++) {
+		target = &cplt->event.target[c];
+
+		for (i = 0; i < ARRAY_SIZE(target->queue); i++)
+			ssam_event_queue_init(cplt, &target->queue[i]);
+	}
+
+	status = ssam_nf_init(&cplt->event.notif);
+	if (status)
+		destroy_workqueue(cplt->wq);
+
+	return status;
+}
+
+/**
+ * ssam_cplt_destroy() - Deinitialize the completion system.
+ * @cplt: The completion system to deinitialize.
+ *
+ * Deinitialize the given completion system and ensure that all pending, i.e.
+ * yet-to-be-completed, event items and requests have been handled.
+ */
+static void ssam_cplt_destroy(struct ssam_cplt *cplt)
+{
+	/*
+	 * Note: destroy_workqueue ensures that all currently queued work will
+	 * be fully completed and the workqueue drained. This means that this
+	 * call will inherently also free any queued ssam_event_items, thus we
+	 * don't have to take care of that here explicitly.
+	 */
+	destroy_workqueue(cplt->wq);
+	ssam_nf_destroy(&cplt->event.notif);
+}
+
+
+/* -- Main SSAM device structures. ------------------------------------------ */
+
+/**
+ * ssam_controller_device() - Get the &struct device associated with this
+ * controller.
+ * @c: The controller for which to get the device.
+ *
+ * Return: Returns the &struct device associated with this controller,
+ * providing its lower-level transport.
+ */
+struct device *ssam_controller_device(struct ssam_controller *c)
+{
+	return ssh_rtl_get_device(&c->rtl);
+}
+EXPORT_SYMBOL_GPL(ssam_controller_device);
+
+static void __ssam_controller_release(struct kref *kref)
+{
+	struct ssam_controller *ctrl = to_ssam_controller(kref, kref);
+
+	/*
+	 * The lock-call here is to satisfy lockdep. At this point we really
+	 * expect this to be the last remaining reference to the controller.
+	 * Anything else is a bug.
+	 */
+	ssam_controller_lock(ctrl);
+	ssam_controller_destroy(ctrl);
+	ssam_controller_unlock(ctrl);
+
+	kfree(ctrl);
+}
+
+/**
+ * ssam_controller_get() - Increment reference count of controller.
+ * @c: The controller.
+ *
+ * Return: Returns the controller provided as input.
+ */
+struct ssam_controller *ssam_controller_get(struct ssam_controller *c)
+{
+	if (c)
+		kref_get(&c->kref);
+	return c;
+}
+EXPORT_SYMBOL_GPL(ssam_controller_get);
+
+/**
+ * ssam_controller_put() - Decrement reference count of controller.
+ * @c: The controller.
+ */
+void ssam_controller_put(struct ssam_controller *c)
+{
+	if (c)
+		kref_put(&c->kref, __ssam_controller_release);
+}
+EXPORT_SYMBOL_GPL(ssam_controller_put);
+
+/**
+ * ssam_controller_statelock() - Lock the controller against state transitions.
+ * @c: The controller to lock.
+ *
+ * Lock the controller against state transitions. Holding this lock guarantees
+ * that the controller will not transition between states, i.e. if the
+ * controller is in state "started", when this lock has been acquired, it will
+ * remain in this state at least until the lock has been released.
+ *
+ * Multiple clients may concurrently hold this lock. In other words: The
+ * ``statelock`` functions represent the read-lock part of a r/w-semaphore.
+ * Actions causing state transitions of the controller must be executed while
+ * holding the write-part of this r/w-semaphore (see ssam_controller_lock()
+ * and ssam_controller_unlock() for that).
+ *
+ * See ssam_controller_stateunlock() for the corresponding unlock function.
+ */
+void ssam_controller_statelock(struct ssam_controller *c)
+{
+	down_read(&c->lock);
+}
+EXPORT_SYMBOL_GPL(ssam_controller_statelock);
+
+/**
+ * ssam_controller_stateunlock() - Unlock controller state transitions.
+ * @c: The controller to unlock.
+ *
+ * See ssam_controller_statelock() for the corresponding lock function.
+ */
+void ssam_controller_stateunlock(struct ssam_controller *c)
+{
+	up_read(&c->lock);
+}
+EXPORT_SYMBOL_GPL(ssam_controller_stateunlock);
+
+/**
+ * ssam_controller_lock() - Acquire the main controller lock.
+ * @c: The controller to lock.
+ *
+ * This lock must be held for any state transitions, including transition to
+ * suspend/resumed states and during shutdown. See ssam_controller_statelock()
+ * for more details on controller locking.
+ *
+ * See ssam_controller_unlock() for the corresponding unlock function.
+ */
+void ssam_controller_lock(struct ssam_controller *c)
+{
+	down_write(&c->lock);
+}
+
+/*
+ * ssam_controller_unlock() - Release the main controller lock.
+ * @c: The controller to unlock.
+ *
+ * See ssam_controller_lock() for the corresponding lock function.
+ */
+void ssam_controller_unlock(struct ssam_controller *c)
+{
+	up_write(&c->lock);
+}
+
+static void ssam_handle_event(struct ssh_rtl *rtl,
+			      const struct ssh_command *cmd,
+			      const struct ssam_span *data)
+{
+	struct ssam_controller *ctrl = to_ssam_controller(rtl, rtl);
+	struct ssam_event_item *item;
+
+	item = ssam_event_item_alloc(data->len, GFP_KERNEL);
+	if (!item)
+		return;
+
+	item->rqid = get_unaligned_le16(&cmd->rqid);
+	item->event.target_category = cmd->tc;
+	item->event.target_id = cmd->tid_in;
+	item->event.command_id = cmd->cid;
+	item->event.instance_id = cmd->iid;
+	memcpy(&item->event.data[0], data->ptr, data->len);
+
+	if (WARN_ON(ssam_cplt_submit_event(&ctrl->cplt, item)))
+		ssam_event_item_free(item);
+}
+
+static const struct ssh_rtl_ops ssam_rtl_ops = {
+	.handle_event = ssam_handle_event,
+};
+
+static bool ssam_notifier_is_empty(struct ssam_controller *ctrl);
+static void ssam_notifier_unregister_all(struct ssam_controller *ctrl);
+
+#define SSAM_SSH_DSM_REVISION	0
+
+/* d5e383e1-d892-4a76-89fc-f6aaae7ed5b5 */
+static const guid_t SSAM_SSH_DSM_GUID =
+	GUID_INIT(0xd5e383e1, 0xd892, 0x4a76,
+		  0x89, 0xfc, 0xf6, 0xaa, 0xae, 0x7e, 0xd5, 0xb5);
+
+enum ssh_dsm_fn {
+	SSH_DSM_FN_SSH_POWER_PROFILE             = 0x05,
+	SSH_DSM_FN_SCREEN_ON_SLEEP_IDLE_TIMEOUT  = 0x06,
+	SSH_DSM_FN_SCREEN_OFF_SLEEP_IDLE_TIMEOUT = 0x07,
+	SSH_DSM_FN_D3_CLOSES_HANDLE              = 0x08,
+	SSH_DSM_FN_SSH_BUFFER_SIZE               = 0x09,
+};
+
+static int ssam_dsm_get_functions(acpi_handle handle, u64 *funcs)
+{
+	union acpi_object *obj;
+	u64 mask = 0;
+	int i;
+
+	*funcs = 0;
+
+	/*
+	 * The _DSM function is only present on newer models. It is not
+	 * present on 5th and 6th generation devices (i.e. up to and including
+	 * Surface Pro 6, Surface Laptop 2, Surface Book 2).
+	 *
+	 * If the _DSM is not present, indicate that no function is supported.
+	 * This will result in default values being set.
+	 */
+	if (!acpi_has_method(handle, "_DSM"))
+		return 0;
+
+	obj = acpi_evaluate_dsm_typed(handle, &SSAM_SSH_DSM_GUID,
+				      SSAM_SSH_DSM_REVISION, 0, NULL,
+				      ACPI_TYPE_BUFFER);
+	if (!obj)
+		return -EIO;
+
+	for (i = 0; i < obj->buffer.length && i < 8; i++)
+		mask |= (((u64)obj->buffer.pointer[i]) << (i * 8));
+
+	if (mask & BIT(0))
+		*funcs = mask;
+
+	ACPI_FREE(obj);
+	return 0;
+}
+
+static int ssam_dsm_load_u32(acpi_handle handle, u64 funcs, u64 func, u32 *ret)
+{
+	union acpi_object *obj;
+	u64 val;
+
+	if (!(funcs & BIT_ULL(func)))
+		return 0; /* Not supported, leave *ret at its default value */
+
+	obj = acpi_evaluate_dsm_typed(handle, &SSAM_SSH_DSM_GUID,
+				      SSAM_SSH_DSM_REVISION, func, NULL,
+				      ACPI_TYPE_INTEGER);
+	if (!obj)
+		return -EIO;
+
+	val = obj->integer.value;
+	ACPI_FREE(obj);
+
+	if (val > U32_MAX)
+		return -ERANGE;
+
+	*ret = val;
+	return 0;
+}
+
+/**
+ * ssam_controller_caps_load_from_acpi() - Load controller capabilities from
+ * ACPI _DSM.
+ * @handle: The handle of the ACPI controller/SSH device.
+ * @caps:   Where to store the capabilities in.
+ *
+ * Initializes the given controller capabilities with default values, then
+ * checks and, if the respective _DSM functions are available, loads the
+ * actual capabilities from the _DSM.
+ *
+ * Return: Returns zero on success, a negative error code on failure.
+ */
+static
+int ssam_controller_caps_load_from_acpi(acpi_handle handle,
+					struct ssam_controller_caps *caps)
+{
+	u32 d3_closes_handle = false;
+	u64 funcs;
+	int status;
+
+	/* Set defaults. */
+	caps->ssh_power_profile = U32_MAX;
+	caps->screen_on_sleep_idle_timeout = U32_MAX;
+	caps->screen_off_sleep_idle_timeout = U32_MAX;
+	caps->d3_closes_handle = false;
+	caps->ssh_buffer_size = U32_MAX;
+
+	/* Pre-load supported DSM functions. */
+	status = ssam_dsm_get_functions(handle, &funcs);
+	if (status)
+		return status;
+
+	/* Load actual values from ACPI, if present. */
+	status = ssam_dsm_load_u32(handle, funcs, SSH_DSM_FN_SSH_POWER_PROFILE,
+				   &caps->ssh_power_profile);
+	if (status)
+		return status;
+
+	status = ssam_dsm_load_u32(handle, funcs,
+				   SSH_DSM_FN_SCREEN_ON_SLEEP_IDLE_TIMEOUT,
+				   &caps->screen_on_sleep_idle_timeout);
+	if (status)
+		return status;
+
+	status = ssam_dsm_load_u32(handle, funcs,
+				   SSH_DSM_FN_SCREEN_OFF_SLEEP_IDLE_TIMEOUT,
+				   &caps->screen_off_sleep_idle_timeout);
+	if (status)
+		return status;
+
+	status = ssam_dsm_load_u32(handle, funcs, SSH_DSM_FN_D3_CLOSES_HANDLE,
+				   &d3_closes_handle);
+	if (status)
+		return status;
+
+	caps->d3_closes_handle = !!d3_closes_handle;
+
+	status = ssam_dsm_load_u32(handle, funcs, SSH_DSM_FN_SSH_BUFFER_SIZE,
+				   &caps->ssh_buffer_size);
+	if (status)
+		return status;
+
+	return 0;
+}
+
+/**
+ * ssam_controller_init() - Initialize SSAM controller.
+ * @ctrl:   The controller to initialize.
+ * @serdev: The serial device representing the underlying data transport.
+ *
+ * Initializes the given controller. Does neither start receiver nor
+ * transmitter threads. After this call, the controller has to be hooked up to
+ * the serdev core separately via &struct serdev_device_ops, relaying calls to
+ * ssam_controller_receive_buf() and ssam_controller_write_wakeup(). Once the
+ * controller has been hooked up, transmitter and receiver threads may be
+ * started via ssam_controller_start(). These setup steps need to be completed
+ * before controller can be used for requests.
+ */
+int ssam_controller_init(struct ssam_controller *ctrl,
+			 struct serdev_device *serdev)
+{
+	acpi_handle handle = ACPI_HANDLE(&serdev->dev);
+	int status;
+
+	init_rwsem(&ctrl->lock);
+	kref_init(&ctrl->kref);
+
+	status = ssam_controller_caps_load_from_acpi(handle, &ctrl->caps);
+	if (status)
+		return status;
+
+	dev_dbg(&serdev->dev,
+		"device capabilities:\n"
+		"  ssh_power_profile:             %u\n"
+		"  ssh_buffer_size:               %u\n"
+		"  screen_on_sleep_idle_timeout:  %u\n"
+		"  screen_off_sleep_idle_timeout: %u\n"
+		"  d3_closes_handle:              %u\n",
+		ctrl->caps.ssh_power_profile,
+		ctrl->caps.ssh_buffer_size,
+		ctrl->caps.screen_on_sleep_idle_timeout,
+		ctrl->caps.screen_off_sleep_idle_timeout,
+		ctrl->caps.d3_closes_handle);
+
+	ssh_seq_reset(&ctrl->counter.seq);
+	ssh_rqid_reset(&ctrl->counter.rqid);
+
+	/* Initialize event/request completion system. */
+	status = ssam_cplt_init(&ctrl->cplt, &serdev->dev);
+	if (status)
+		return status;
+
+	/* Initialize request and packet transport layers. */
+	status = ssh_rtl_init(&ctrl->rtl, serdev, &ssam_rtl_ops);
+	if (status) {
+		ssam_cplt_destroy(&ctrl->cplt);
+		return status;
+	}
+
+	/*
+	 * Set state via write_once even though we expect to be in an
+	 * exclusive context, due to smoke-testing in
+	 * ssam_request_sync_submit().
+	 */
+	WRITE_ONCE(ctrl->state, SSAM_CONTROLLER_INITIALIZED);
+	return 0;
+}
+
+/**
+ * ssam_controller_start() - Start the receiver and transmitter threads of the
+ * controller.
+ * @ctrl: The controller.
+ *
+ * Note: When this function is called, the controller should be properly
+ * hooked up to the serdev core via &struct serdev_device_ops. Please refer
+ * to ssam_controller_init() for more details on controller initialization.
+ *
+ * This function must be called with the main controller lock held (i.e. by
+ * calling ssam_controller_lock()).
+ */
+int ssam_controller_start(struct ssam_controller *ctrl)
+{
+	int status;
+
+	lockdep_assert_held_write(&ctrl->lock);
+
+	if (ctrl->state != SSAM_CONTROLLER_INITIALIZED)
+		return -EINVAL;
+
+	status = ssh_rtl_start(&ctrl->rtl);
+	if (status)
+		return status;
+
+	/*
+	 * Set state via write_once even though we expect to be locked/in an
+	 * exclusive context, due to smoke-testing in
+	 * ssam_request_sync_submit().
+	 */
+	WRITE_ONCE(ctrl->state, SSAM_CONTROLLER_STARTED);
+	return 0;
+}
+
+/*
+ * SSAM_CTRL_SHUTDOWN_FLUSH_TIMEOUT - Timeout for flushing requests during
+ * shutdown.
+ *
+ * Chosen to be larger than one full request timeout, including packets timing
+ * out. This value should give ample time to complete any outstanding requests
+ * during normal operation and account for the odd package timeout.
+ */
+#define SSAM_CTRL_SHUTDOWN_FLUSH_TIMEOUT	msecs_to_jiffies(5000)
+
+/**
+ * ssam_controller_shutdown() - Shut down the controller.
+ * @ctrl: The controller.
+ *
+ * Shuts down the controller by flushing all pending requests and stopping the
+ * transmitter and receiver threads. All requests submitted after this call
+ * will fail with %-ESHUTDOWN. While it is discouraged to do so, this function
+ * is safe to use in parallel with ongoing request submission.
+ *
+ * In the course of this shutdown procedure, all currently registered
+ * notifiers will be unregistered. It is, however, strongly recommended to not
+ * rely on this behavior, and instead the party registering the notifier
+ * should unregister it before the controller gets shut down, e.g. via the
+ * SSAM bus which guarantees client devices to be removed before a shutdown.
+ *
+ * Note that events may still be pending after this call, but, due to the
+ * notifiers being unregistered, these events will be dropped when the
+ * controller is subsequently destroyed via ssam_controller_destroy().
+ *
+ * This function must be called with the main controller lock held (i.e. by
+ * calling ssam_controller_lock()).
+ */
+void ssam_controller_shutdown(struct ssam_controller *ctrl)
+{
+	enum ssam_controller_state s = ctrl->state;
+	int status;
+
+	lockdep_assert_held_write(&ctrl->lock);
+
+	if (s == SSAM_CONTROLLER_UNINITIALIZED || s == SSAM_CONTROLLER_STOPPED)
+		return;
+
+	/*
+	 * Try to flush pending events and requests while everything still
+	 * works. Note: There may still be packets and/or requests in the
+	 * system after this call (e.g. via control packets submitted by the
+	 * packet transport layer or flush timeout / failure, ...). Those will
+	 * be handled with the ssh_rtl_shutdown() call below.
+	 */
+	status = ssh_rtl_flush(&ctrl->rtl, SSAM_CTRL_SHUTDOWN_FLUSH_TIMEOUT);
+	if (status) {
+		ssam_err(ctrl, "failed to flush request transport layer: %d\n",
+			 status);
+	}
+
+	/* Try to flush all currently completing requests and events. */
+	ssam_cplt_flush(&ctrl->cplt);
+
+	/*
+	 * We expect all notifiers to have been removed by the respective client
+	 * driver that set them up at this point. If this warning occurs, some
+	 * client driver has not done that...
+	 */
+	WARN_ON(!ssam_notifier_is_empty(ctrl));
+
+	/*
+	 * Nevertheless, we should still take care of drivers that don't behave
+	 * well. Thus disable all enabled events, unregister all notifiers.
+	 */
+	ssam_notifier_unregister_all(ctrl);
+
+	/*
+	 * Cancel remaining requests. Ensure no new ones can be queued and stop
+	 * threads.
+	 */
+	ssh_rtl_shutdown(&ctrl->rtl);
+
+	/*
+	 * Set state via write_once even though we expect to be locked/in an
+	 * exclusive context, due to smoke-testing in
+	 * ssam_request_sync_submit().
+	 */
+	WRITE_ONCE(ctrl->state, SSAM_CONTROLLER_STOPPED);
+	ctrl->rtl.ptl.serdev = NULL;
+}
+
+/**
+ * ssam_controller_destroy() - Destroy the controller and free its resources.
+ * @ctrl: The controller.
+ *
+ * Ensures that all resources associated with the controller get freed. This
+ * function should only be called after the controller has been stopped via
+ * ssam_controller_shutdown(). In general, this function should not be called
+ * directly. The only valid place to call this function directly is during
+ * initialization, before the controller has been fully initialized and passed
+ * to other processes. This function is called automatically when the
+ * reference count of the controller reaches zero.
+ *
+ * This function must be called with the main controller lock held (i.e. by
+ * calling ssam_controller_lock()).
+ */
+void ssam_controller_destroy(struct ssam_controller *ctrl)
+{
+	lockdep_assert_held_write(&ctrl->lock);
+
+	if (ctrl->state == SSAM_CONTROLLER_UNINITIALIZED)
+		return;
+
+	WARN_ON(ctrl->state != SSAM_CONTROLLER_STOPPED);
+
+	/*
+	 * Note: New events could still have been received after the previous
+	 * flush in ssam_controller_shutdown, before the request transport layer
+	 * has been shut down. At this point, after the shutdown, we can be sure
+	 * that no new events will be queued. The call to ssam_cplt_destroy will
+	 * ensure that those remaining are being completed and freed.
+	 */
+
+	/* Actually free resources. */
+	ssam_cplt_destroy(&ctrl->cplt);
+	ssh_rtl_destroy(&ctrl->rtl);
+
+	/*
+	 * Set state via write_once even though we expect to be locked/in an
+	 * exclusive context, due to smoke-testing in
+	 * ssam_request_sync_submit().
+	 */
+	WRITE_ONCE(ctrl->state, SSAM_CONTROLLER_UNINITIALIZED);
+}
+
+/**
+ * ssam_controller_suspend() - Suspend the controller.
+ * @ctrl: The controller to suspend.
+ *
+ * Marks the controller as suspended. Note that display-off and D0-exit
+ * notifications have to be sent manually before transitioning the controller
+ * into the suspended state via this function.
+ *
+ * See ssam_controller_resume() for the corresponding resume function.
+ *
+ * Return: Returns %-EINVAL if the controller is currently not in the
+ * "started" state.
+ */
+int ssam_controller_suspend(struct ssam_controller *ctrl)
+{
+	ssam_controller_lock(ctrl);
+
+	if (ctrl->state != SSAM_CONTROLLER_STARTED) {
+		ssam_controller_unlock(ctrl);
+		return -EINVAL;
+	}
+
+	ssam_dbg(ctrl, "pm: suspending controller\n");
+
+	/*
+	 * Set state via write_once even though we're locked, due to
+	 * smoke-testing in ssam_request_sync_submit().
+	 */
+	WRITE_ONCE(ctrl->state, SSAM_CONTROLLER_SUSPENDED);
+
+	ssam_controller_unlock(ctrl);
+	return 0;
+}
+
+/**
+ * ssam_controller_resume() - Resume the controller from suspend.
+ * @ctrl: The controller to resume.
+ *
+ * Resume the controller from the suspended state it was put into via
+ * ssam_controller_suspend(). This function does not issue display-on and
+ * D0-entry notifications. If required, those have to be sent manually after
+ * this call.
+ *
+ * Return: Returns %-EINVAL if the controller is currently not suspended.
+ */
+int ssam_controller_resume(struct ssam_controller *ctrl)
+{
+	ssam_controller_lock(ctrl);
+
+	if (ctrl->state != SSAM_CONTROLLER_SUSPENDED) {
+		ssam_controller_unlock(ctrl);
+		return -EINVAL;
+	}
+
+	ssam_dbg(ctrl, "pm: resuming controller\n");
+
+	/*
+	 * Set state via write_once even though we're locked, due to
+	 * smoke-testing in ssam_request_sync_submit().
+	 */
+	WRITE_ONCE(ctrl->state, SSAM_CONTROLLER_STARTED);
+
+	ssam_controller_unlock(ctrl);
+	return 0;
+}
+
+
+/* -- Top-level request interface ------------------------------------------- */
+
+/**
+ * ssam_request_write_data() - Construct and write SAM request message to
+ * buffer.
+ * @buf:  The buffer to write the data to.
+ * @ctrl: The controller via which the request will be sent.
+ * @spec: The request data and specification.
+ *
+ * Constructs a SAM/SSH request message and writes it to the provided buffer.
+ * The request and transport counters, specifically RQID and SEQ, will be set
+ * in this call. These counters are obtained from the controller. It is thus
+ * only valid to send the resulting message via the controller specified here.
+ *
+ * For calculation of the required buffer size, refer to the
+ * SSH_COMMAND_MESSAGE_LENGTH() macro.
+ *
+ * Return: Returns the number of bytes used in the buffer on success. Returns
+ * %-EINVAL if the payload length provided in the request specification is too
+ * large (larger than %SSH_COMMAND_MAX_PAYLOAD_SIZE) or if the provided buffer
+ * is too small.
+ */
+ssize_t ssam_request_write_data(struct ssam_span *buf,
+				struct ssam_controller *ctrl,
+				const struct ssam_request *spec)
+{
+	struct msgbuf msgb;
+	u16 rqid;
+	u8 seq;
+
+	if (spec->length > SSH_COMMAND_MAX_PAYLOAD_SIZE)
+		return -EINVAL;
+
+	if (SSH_COMMAND_MESSAGE_LENGTH(spec->length) > buf->len)
+		return -EINVAL;
+
+	msgb_init(&msgb, buf->ptr, buf->len);
+	seq = ssh_seq_next(&ctrl->counter.seq);
+	rqid = ssh_rqid_next(&ctrl->counter.rqid);
+	msgb_push_cmd(&msgb, seq, rqid, spec);
+
+	return msgb_bytes_used(&msgb);
+}
+EXPORT_SYMBOL_GPL(ssam_request_write_data);
+
+static void ssam_request_sync_complete(struct ssh_request *rqst,
+				       const struct ssh_command *cmd,
+				       const struct ssam_span *data, int status)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+	struct ssam_request_sync *r;
+
+	r = container_of(rqst, struct ssam_request_sync, base);
+	r->status = status;
+
+	if (r->resp)
+		r->resp->length = 0;
+
+	if (status) {
+		rtl_dbg_cond(rtl, "rsp: request failed: %d\n", status);
+		return;
+	}
+
+	if (!data)	/* Handle requests without a response. */
+		return;
+
+	if (!r->resp || !r->resp->pointer) {
+		if (data->len)
+			rtl_warn(rtl, "rsp: no response buffer provided, dropping data\n");
+		return;
+	}
+
+	if (data->len > r->resp->capacity) {
+		rtl_err(rtl,
+			"rsp: response buffer too small, capacity: %zu bytes, got: %zu bytes\n",
+			r->resp->capacity, data->len);
+		r->status = -ENOSPC;
+		return;
+	}
+
+	r->resp->length = data->len;
+	memcpy(r->resp->pointer, data->ptr, data->len);
+}
+
+static void ssam_request_sync_release(struct ssh_request *rqst)
+{
+	complete_all(&container_of(rqst, struct ssam_request_sync, base)->comp);
+}
+
+static const struct ssh_request_ops ssam_request_sync_ops = {
+	.release = ssam_request_sync_release,
+	.complete = ssam_request_sync_complete,
+};
+
+/**
+ * ssam_request_sync_alloc() - Allocate a synchronous request.
+ * @payload_len: The length of the request payload.
+ * @flags:       Flags used for allocation.
+ * @rqst:        Where to store the pointer to the allocated request.
+ * @buffer:      Where to store the buffer descriptor for the message buffer of
+ *               the request.
+ *
+ * Allocates a synchronous request with corresponding message buffer. The
+ * request still needs to be initialized ssam_request_sync_init() before
+ * it can be submitted, and the message buffer data must still be set to the
+ * returned buffer via ssam_request_sync_set_data() after it has been filled,
+ * if need be with adjusted message length.
+ *
+ * After use, the request and its corresponding message buffer should be freed
+ * via ssam_request_sync_free(). The buffer must not be freed separately.
+ *
+ * Return: Returns zero on success, %-ENOMEM if the request could not be
+ * allocated.
+ */
+int ssam_request_sync_alloc(size_t payload_len, gfp_t flags,
+			    struct ssam_request_sync **rqst,
+			    struct ssam_span *buffer)
+{
+	size_t msglen = SSH_COMMAND_MESSAGE_LENGTH(payload_len);
+
+	*rqst = kzalloc(sizeof(**rqst) + msglen, flags);
+	if (!*rqst)
+		return -ENOMEM;
+
+	buffer->ptr = (u8 *)(*rqst + 1);
+	buffer->len = msglen;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ssam_request_sync_alloc);
+
+/**
+ * ssam_request_sync_free() - Free a synchronous request.
+ * @rqst: The request to be freed.
+ *
+ * Free a synchronous request and its corresponding buffer allocated with
+ * ssam_request_sync_alloc(). Do not use for requests allocated on the stack
+ * or via any other function.
+ *
+ * Warning: The caller must ensure that the request is not in use any more.
+ * I.e. the caller must ensure that it has the only reference to the request
+ * and the request is not currently pending. This means that the caller has
+ * either never submitted the request, request submission has failed, or the
+ * caller has waited until the submitted request has been completed via
+ * ssam_request_sync_wait().
+ */
+void ssam_request_sync_free(struct ssam_request_sync *rqst)
+{
+	kfree(rqst);
+}
+EXPORT_SYMBOL_GPL(ssam_request_sync_free);
+
+/**
+ * ssam_request_sync_init() - Initialize a synchronous request struct.
+ * @rqst:  The request to initialize.
+ * @flags: The request flags.
+ *
+ * Initializes the given request struct. Does not initialize the request
+ * message data. This has to be done explicitly after this call via
+ * ssam_request_sync_set_data() and the actual message data has to be written
+ * via ssam_request_write_data().
+ *
+ * Return: Returns zero on success or %-EINVAL if the given flags are invalid.
+ */
+int ssam_request_sync_init(struct ssam_request_sync *rqst,
+			   enum ssam_request_flags flags)
+{
+	int status;
+
+	status = ssh_request_init(&rqst->base, flags, &ssam_request_sync_ops);
+	if (status)
+		return status;
+
+	init_completion(&rqst->comp);
+	rqst->resp = NULL;
+	rqst->status = 0;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ssam_request_sync_init);
+
+/**
+ * ssam_request_sync_submit() - Submit a synchronous request.
+ * @ctrl: The controller with which to submit the request.
+ * @rqst: The request to submit.
+ *
+ * Submit a synchronous request. The request has to be initialized and
+ * properly set up, including response buffer (may be %NULL if no response is
+ * expected) and command message data. This function does not wait for the
+ * request to be completed.
+ *
+ * If this function succeeds, ssam_request_sync_wait() must be used to ensure
+ * that the request has been completed before the response data can be
+ * accessed and/or the request can be freed. On failure, the request may
+ * immediately be freed.
+ *
+ * This function may only be used if the controller is active, i.e. has been
+ * initialized and not suspended.
+ */
+int ssam_request_sync_submit(struct ssam_controller *ctrl,
+			     struct ssam_request_sync *rqst)
+{
+	int status;
+
+	/*
+	 * This is only a superficial check. In general, the caller needs to
+	 * ensure that the controller is initialized and is not (and does not
+	 * get) suspended during use, i.e. until the request has been completed
+	 * (if _absolutely_ necessary, by use of ssam_controller_statelock/
+	 * ssam_controller_stateunlock, but something like ssam_client_link
+	 * should be preferred as this needs to last until the request has been
+	 * completed).
+	 *
+	 * Note that it is actually safe to use this function while the
+	 * controller is in the process of being shut down (as ssh_rtl_submit
+	 * is safe with regards to this), but it is generally discouraged to do
+	 * so.
+	 */
+	if (WARN_ON(READ_ONCE(ctrl->state) != SSAM_CONTROLLER_STARTED)) {
+		ssh_request_put(&rqst->base);
+		return -ENODEV;
+	}
+
+	status = ssh_rtl_submit(&ctrl->rtl, &rqst->base);
+	ssh_request_put(&rqst->base);
+
+	return status;
+}
+EXPORT_SYMBOL_GPL(ssam_request_sync_submit);
+
+/**
+ * ssam_request_sync() - Execute a synchronous request.
+ * @ctrl: The controller via which the request will be submitted.
+ * @spec: The request specification and payload.
+ * @rsp:  The response buffer.
+ *
+ * Allocates a synchronous request with its message data buffer on the heap
+ * via ssam_request_sync_alloc(), fully initializes it via the provided
+ * request specification, submits it, and finally waits for its completion
+ * before freeing it and returning its status.
+ *
+ * Return: Returns the status of the request or any failure during setup.
+ */
+int ssam_request_sync(struct ssam_controller *ctrl,
+		      const struct ssam_request *spec,
+		      struct ssam_response *rsp)
+{
+	struct ssam_request_sync *rqst;
+	struct ssam_span buf;
+	ssize_t len;
+	int status;
+
+	status = ssam_request_sync_alloc(spec->length, GFP_KERNEL, &rqst, &buf);
+	if (status)
+		return status;
+
+	status = ssam_request_sync_init(rqst, spec->flags);
+	if (status) {
+		ssam_request_sync_free(rqst);
+		return status;
+	}
+
+	ssam_request_sync_set_resp(rqst, rsp);
+
+	len = ssam_request_write_data(&buf, ctrl, spec);
+	if (len < 0) {
+		ssam_request_sync_free(rqst);
+		return len;
+	}
+
+	ssam_request_sync_set_data(rqst, buf.ptr, len);
+
+	status = ssam_request_sync_submit(ctrl, rqst);
+	if (!status)
+		status = ssam_request_sync_wait(rqst);
+
+	ssam_request_sync_free(rqst);
+	return status;
+}
+EXPORT_SYMBOL_GPL(ssam_request_sync);
+
+/**
+ * ssam_request_sync_with_buffer() - Execute a synchronous request with the
+ * provided buffer as back-end for the message buffer.
+ * @ctrl: The controller via which the request will be submitted.
+ * @spec: The request specification and payload.
+ * @rsp:  The response buffer.
+ * @buf:  The buffer for the request message data.
+ *
+ * Allocates a synchronous request struct on the stack, fully initializes it
+ * using the provided buffer as message data buffer, submits it, and then
+ * waits for its completion before returning its status. The
+ * SSH_COMMAND_MESSAGE_LENGTH() macro can be used to compute the required
+ * message buffer size.
+ *
+ * This function does essentially the same as ssam_request_sync(), but instead
+ * of dynamically allocating the request and message data buffer, it uses the
+ * provided message data buffer and stores the (small) request struct on the
+ * heap.
+ *
+ * Return: Returns the status of the request or any failure during setup.
+ */
+int ssam_request_sync_with_buffer(struct ssam_controller *ctrl,
+				  const struct ssam_request *spec,
+				  struct ssam_response *rsp,
+				  struct ssam_span *buf)
+{
+	struct ssam_request_sync rqst;
+	ssize_t len;
+	int status;
+
+	status = ssam_request_sync_init(&rqst, spec->flags);
+	if (status)
+		return status;
+
+	ssam_request_sync_set_resp(&rqst, rsp);
+
+	len = ssam_request_write_data(buf, ctrl, spec);
+	if (len < 0)
+		return len;
+
+	ssam_request_sync_set_data(&rqst, buf->ptr, len);
+
+	status = ssam_request_sync_submit(ctrl, &rqst);
+	if (!status)
+		status = ssam_request_sync_wait(&rqst);
+
+	return status;
+}
+EXPORT_SYMBOL_GPL(ssam_request_sync_with_buffer);
+
+
+/* -- Internal SAM requests. ------------------------------------------------ */
+
+SSAM_DEFINE_SYNC_REQUEST_R(ssam_ssh_get_firmware_version, __le32, {
+	.target_category = SSAM_SSH_TC_SAM,
+	.target_id       = 0x01,
+	.command_id      = 0x13,
+	.instance_id     = 0x00,
+});
+
+SSAM_DEFINE_SYNC_REQUEST_R(ssam_ssh_notif_display_off, u8, {
+	.target_category = SSAM_SSH_TC_SAM,
+	.target_id       = 0x01,
+	.command_id      = 0x15,
+	.instance_id     = 0x00,
+});
+
+SSAM_DEFINE_SYNC_REQUEST_R(ssam_ssh_notif_display_on, u8, {
+	.target_category = SSAM_SSH_TC_SAM,
+	.target_id       = 0x01,
+	.command_id      = 0x16,
+	.instance_id     = 0x00,
+});
+
+SSAM_DEFINE_SYNC_REQUEST_R(ssam_ssh_notif_d0_exit, u8, {
+	.target_category = SSAM_SSH_TC_SAM,
+	.target_id       = 0x01,
+	.command_id      = 0x33,
+	.instance_id     = 0x00,
+});
+
+SSAM_DEFINE_SYNC_REQUEST_R(ssam_ssh_notif_d0_entry, u8, {
+	.target_category = SSAM_SSH_TC_SAM,
+	.target_id       = 0x01,
+	.command_id      = 0x34,
+	.instance_id     = 0x00,
+});
+
+/**
+ * struct ssh_notification_params - Command payload to enable/disable SSH
+ * notifications.
+ * @target_category: The target category for which notifications should be
+ *                   enabled/disabled.
+ * @flags:           Flags determining how notifications are being sent.
+ * @request_id:      The request ID that is used to send these notifications.
+ * @instance_id:     The specific instance in the given target category for
+ *                   which notifications should be enabled.
+ */
+struct ssh_notification_params {
+	u8 target_category;
+	u8 flags;
+	__le16 request_id;
+	u8 instance_id;
+} __packed;
+
+static_assert(sizeof(struct ssh_notification_params) == 5);
+
+static int __ssam_ssh_event_request(struct ssam_controller *ctrl,
+				    struct ssam_event_registry reg, u8 cid,
+				    struct ssam_event_id id, u8 flags)
+{
+	struct ssh_notification_params params;
+	struct ssam_request rqst;
+	struct ssam_response result;
+	int status;
+
+	u16 rqid = ssh_tc_to_rqid(id.target_category);
+	u8 buf = 0;
+
+	/* Only allow RQIDs that lie within the event spectrum. */
+	if (!ssh_rqid_is_event(rqid))
+		return -EINVAL;
+
+	params.target_category = id.target_category;
+	params.instance_id = id.instance;
+	params.flags = flags;
+	put_unaligned_le16(rqid, &params.request_id);
+
+	rqst.target_category = reg.target_category;
+	rqst.target_id = reg.target_id;
+	rqst.command_id = cid;
+	rqst.instance_id = 0x00;
+	rqst.flags = SSAM_REQUEST_HAS_RESPONSE;
+	rqst.length = sizeof(params);
+	rqst.payload = (u8 *)&params;
+
+	result.capacity = sizeof(buf);
+	result.length = 0;
+	result.pointer = &buf;
+
+	status = ssam_retry(ssam_request_sync_onstack, ctrl, &rqst, &result,
+			    sizeof(params));
+
+	return status < 0 ? status : buf;
+}
+
+/**
+ * ssam_ssh_event_enable() - Enable SSH event.
+ * @ctrl:  The controller for which to enable the event.
+ * @reg:   The event registry describing what request to use for enabling and
+ *         disabling the event.
+ * @id:    The event identifier.
+ * @flags: The event flags.
+ *
+ * Enables the specified event on the EC. This function does not manage
+ * reference counting of enabled events and is basically only a wrapper for
+ * the raw EC request. If the specified event is already enabled, the EC will
+ * ignore this request.
+ *
+ * Return: Returns the status of the executed SAM request (zero on success and
+ * negative on direct failure) or %-EPROTO if the request response indicates a
+ * failure.
+ */
+static int ssam_ssh_event_enable(struct ssam_controller *ctrl,
+				 struct ssam_event_registry reg,
+				 struct ssam_event_id id, u8 flags)
+{
+	int status;
+
+	status = __ssam_ssh_event_request(ctrl, reg, reg.cid_enable, id, flags);
+
+	if (status < 0 && status != -EINVAL) {
+		ssam_err(ctrl,
+			 "failed to enable event source (tc: %#04x, iid: %#04x, reg: %#04x)\n",
+			 id.target_category, id.instance, reg.target_category);
+	}
+
+	if (status > 0) {
+		ssam_err(ctrl,
+			 "unexpected result while enabling event source: %#04x (tc: %#04x, iid: %#04x, reg: %#04x)\n",
+			 status, id.target_category, id.instance, reg.target_category);
+		return -EPROTO;
+	}
+
+	return status;
+}
+
+/**
+ * ssam_ssh_event_disable() - Disable SSH event.
+ * @ctrl:  The controller for which to disable the event.
+ * @reg:   The event registry describing what request to use for enabling and
+ *         disabling the event (must be same as used when enabling the event).
+ * @id:    The event identifier.
+ * @flags: The event flags (likely ignored for disabling of events).
+ *
+ * Disables the specified event on the EC. This function does not manage
+ * reference counting of enabled events and is basically only a wrapper for
+ * the raw EC request. If the specified event is already disabled, the EC will
+ * ignore this request.
+ *
+ * Return: Returns the status of the executed SAM request (zero on success and
+ * negative on direct failure) or %-EPROTO if the request response indicates a
+ * failure.
+ */
+static int ssam_ssh_event_disable(struct ssam_controller *ctrl,
+				  struct ssam_event_registry reg,
+				  struct ssam_event_id id, u8 flags)
+{
+	int status;
+
+	status = __ssam_ssh_event_request(ctrl, reg, reg.cid_disable, id, flags);
+
+	if (status < 0 && status != -EINVAL) {
+		ssam_err(ctrl,
+			 "failed to disable event source (tc: %#04x, iid: %#04x, reg: %#04x)\n",
+			 id.target_category, id.instance, reg.target_category);
+	}
+
+	if (status > 0) {
+		ssam_err(ctrl,
+			 "unexpected result while disabling event source: %#04x (tc: %#04x, iid: %#04x, reg: %#04x)\n",
+			 status, id.target_category, id.instance, reg.target_category);
+		return -EPROTO;
+	}
+
+	return status;
+}
+
+
+/* -- Wrappers for internal SAM requests. ----------------------------------- */
+
+/**
+ * ssam_get_firmware_version() - Get the SAM/EC firmware version.
+ * @ctrl:    The controller.
+ * @version: Where to store the version number.
+ *
+ * Return: Returns zero on success or the status of the executed SAM request
+ * if that request failed.
+ */
+int ssam_get_firmware_version(struct ssam_controller *ctrl, u32 *version)
+{
+	__le32 __version;
+	int status;
+
+	status = ssam_retry(ssam_ssh_get_firmware_version, ctrl, &__version);
+	if (status)
+		return status;
+
+	*version = le32_to_cpu(__version);
+	return 0;
+}
+
+/**
+ * ssam_ctrl_notif_display_off() - Notify EC that the display has been turned
+ * off.
+ * @ctrl: The controller.
+ *
+ * Notify the EC that the display has been turned off and the driver may enter
+ * a lower-power state. This will prevent events from being sent directly.
+ * Rather, the EC signals an event by pulling the wakeup GPIO high for as long
+ * as there are pending events. The events then need to be manually released,
+ * one by one, via the GPIO callback request. All pending events accumulated
+ * during this state can also be released by issuing the display-on
+ * notification, e.g. via ssam_ctrl_notif_display_on(), which will also reset
+ * the GPIO.
+ *
+ * On some devices, specifically ones with an integrated keyboard, the keyboard
+ * backlight will be turned off by this call.
+ *
+ * This function will only send the display-off notification command if
+ * display notifications are supported by the EC. Currently all known devices
+ * support these notifications.
+ *
+ * Use ssam_ctrl_notif_display_on() to reverse the effects of this function.
+ *
+ * Return: Returns zero on success or if no request has been executed, the
+ * status of the executed SAM request if that request failed, or %-EPROTO if
+ * an unexpected response has been received.
+ */
+int ssam_ctrl_notif_display_off(struct ssam_controller *ctrl)
+{
+	int status;
+	u8 response;
+
+	ssam_dbg(ctrl, "pm: notifying display off\n");
+
+	status = ssam_retry(ssam_ssh_notif_display_off, ctrl, &response);
+	if (status)
+		return status;
+
+	if (response != 0) {
+		ssam_err(ctrl, "unexpected response from display-off notification: %#04x\n",
+			 response);
+		return -EPROTO;
+	}
+
+	return 0;
+}
+
+/**
+ * ssam_ctrl_notif_display_on() - Notify EC that the display has been turned on.
+ * @ctrl: The controller.
+ *
+ * Notify the EC that the display has been turned back on and the driver has
+ * exited its lower-power state. This notification is the counterpart to the
+ * display-off notification sent via ssam_ctrl_notif_display_off() and will
+ * reverse its effects, including resetting events to their default behavior.
+ *
+ * This function will only send the display-on notification command if display
+ * notifications are supported by the EC. Currently all known devices support
+ * these notifications.
+ *
+ * See ssam_ctrl_notif_display_off() for more details.
+ *
+ * Return: Returns zero on success or if no request has been executed, the
+ * status of the executed SAM request if that request failed, or %-EPROTO if
+ * an unexpected response has been received.
+ */
+int ssam_ctrl_notif_display_on(struct ssam_controller *ctrl)
+{
+	int status;
+	u8 response;
+
+	ssam_dbg(ctrl, "pm: notifying display on\n");
+
+	status = ssam_retry(ssam_ssh_notif_display_on, ctrl, &response);
+	if (status)
+		return status;
+
+	if (response != 0) {
+		ssam_err(ctrl, "unexpected response from display-on notification: %#04x\n",
+			 response);
+		return -EPROTO;
+	}
+
+	return 0;
+}
+
+/**
+ * ssam_ctrl_notif_d0_exit() - Notify EC that the driver/device exits the D0
+ * power state.
+ * @ctrl: The controller
+ *
+ * Notifies the EC that the driver prepares to exit the D0 power state in
+ * favor of a lower-power state. Exact effects of this function related to the
+ * EC are currently unknown.
+ *
+ * This function will only send the D0-exit notification command if D0-state
+ * notifications are supported by the EC. Only newer Surface generations
+ * support these notifications.
+ *
+ * Use ssam_ctrl_notif_d0_entry() to reverse the effects of this function.
+ *
+ * Return: Returns zero on success or if no request has been executed, the
+ * status of the executed SAM request if that request failed, or %-EPROTO if
+ * an unexpected response has been received.
+ */
+int ssam_ctrl_notif_d0_exit(struct ssam_controller *ctrl)
+{
+	int status;
+	u8 response;
+
+	if (!ctrl->caps.d3_closes_handle)
+		return 0;
+
+	ssam_dbg(ctrl, "pm: notifying D0 exit\n");
+
+	status = ssam_retry(ssam_ssh_notif_d0_exit, ctrl, &response);
+	if (status)
+		return status;
+
+	if (response != 0) {
+		ssam_err(ctrl, "unexpected response from D0-exit notification: %#04x\n",
+			 response);
+		return -EPROTO;
+	}
+
+	return 0;
+}
+
+/**
+ * ssam_ctrl_notif_d0_entry() - Notify EC that the driver/device enters the D0
+ * power state.
+ * @ctrl: The controller
+ *
+ * Notifies the EC that the driver has exited a lower-power state and entered
+ * the D0 power state. Exact effects of this function related to the EC are
+ * currently unknown.
+ *
+ * This function will only send the D0-entry notification command if D0-state
+ * notifications are supported by the EC. Only newer Surface generations
+ * support these notifications.
+ *
+ * See ssam_ctrl_notif_d0_exit() for more details.
+ *
+ * Return: Returns zero on success or if no request has been executed, the
+ * status of the executed SAM request if that request failed, or %-EPROTO if
+ * an unexpected response has been received.
+ */
+int ssam_ctrl_notif_d0_entry(struct ssam_controller *ctrl)
+{
+	int status;
+	u8 response;
+
+	if (!ctrl->caps.d3_closes_handle)
+		return 0;
+
+	ssam_dbg(ctrl, "pm: notifying D0 entry\n");
+
+	status = ssam_retry(ssam_ssh_notif_d0_entry, ctrl, &response);
+	if (status)
+		return status;
+
+	if (response != 0) {
+		ssam_err(ctrl, "unexpected response from D0-entry notification: %#04x\n",
+			 response);
+		return -EPROTO;
+	}
+
+	return 0;
+}
+
+
+/* -- Top-level event registry interface. ----------------------------------- */
+
+/**
+ * ssam_nf_refcount_enable() - Enable event for reference count entry if it has
+ * not already been enabled.
+ * @ctrl:  The controller to enable the event on.
+ * @entry: The reference count entry for the event to be enabled.
+ * @flags: The flags used for enabling the event on the EC.
+ *
+ * Enable the event associated with the given reference count entry if the
+ * reference count equals one, i.e. the event has not previously been enabled.
+ * If the event has already been enabled (i.e. reference count not equal to
+ * one), check that the flags used for enabling match and warn about this if
+ * they do not.
+ *
+ * This does not modify the reference count itself, which is done with
+ * ssam_nf_refcount_inc() / ssam_nf_refcount_dec().
+ *
+ * Note: ``nf->lock`` must be held when calling this function.
+ *
+ * Return: Returns zero on success. If the event is enabled by this call,
+ * returns the status of the event-enable EC command.
+ */
+static int ssam_nf_refcount_enable(struct ssam_controller *ctrl,
+				   struct ssam_nf_refcount_entry *entry, u8 flags)
+{
+	const struct ssam_event_registry reg = entry->key.reg;
+	const struct ssam_event_id id = entry->key.id;
+	struct ssam_nf *nf = &ctrl->cplt.event.notif;
+	int status;
+
+	lockdep_assert_held(&nf->lock);
+
+	ssam_dbg(ctrl, "enabling event (reg: %#04x, tc: %#04x, iid: %#04x, rc: %d)\n",
+		 reg.target_category, id.target_category, id.instance, entry->refcount);
+
+	if (entry->refcount == 1) {
+		status = ssam_ssh_event_enable(ctrl, reg, id, flags);
+		if (status)
+			return status;
+
+		entry->flags = flags;
+
+	} else if (entry->flags != flags) {
+		ssam_warn(ctrl,
+			  "inconsistent flags when enabling event: got %#04x, expected %#04x (reg: %#04x, tc: %#04x, iid: %#04x)\n",
+			  flags, entry->flags, reg.target_category, id.target_category,
+			  id.instance);
+	}
+
+	return 0;
+}
+
+/**
+ * ssam_nf_refcount_disable_free() - Disable event for reference count entry if
+ * it is no longer in use and free the corresponding entry.
+ * @ctrl:  The controller to disable the event on.
+ * @entry: The reference count entry for the event to be disabled.
+ * @flags: The flags used for enabling the event on the EC.
+ * @ec:    Flag specifying if the event should actually be disabled on the EC.
+ *
+ * If ``ec`` equals ``true`` and the reference count equals zero (i.e. the
+ * event is no longer requested by any client), the specified event will be
+ * disabled on the EC via the corresponding request.
+ *
+ * If ``ec`` equals ``false``, no request will be sent to the EC and the event
+ * can be considered in a detached state (i.e. no longer used but still
+ * enabled). Disabling an event via this method may be required for
+ * hot-removable devices, where event disable requests may time out after the
+ * device has been physically removed.
+ *
+ * In both cases, if the reference count equals zero, the corresponding
+ * reference count entry will be freed. The reference count entry must not be
+ * used any more after a call to this function.
+ *
+ * Also checks if the flags used for disabling the event match the flags used
+ * for enabling the event and warns if they do not (regardless of reference
+ * count).
+ *
+ * This does not modify the reference count itself, which is done with
+ * ssam_nf_refcount_inc() / ssam_nf_refcount_dec().
+ *
+ * Note: ``nf->lock`` must be held when calling this function.
+ *
+ * Return: Returns zero on success. If the event is disabled by this call,
+ * returns the status of the event-enable EC command.
+ */
+static int ssam_nf_refcount_disable_free(struct ssam_controller *ctrl,
+					 struct ssam_nf_refcount_entry *entry, u8 flags, bool ec)
+{
+	const struct ssam_event_registry reg = entry->key.reg;
+	const struct ssam_event_id id = entry->key.id;
+	struct ssam_nf *nf = &ctrl->cplt.event.notif;
+	int status = 0;
+
+	lockdep_assert_held(&nf->lock);
+
+	ssam_dbg(ctrl, "%s event (reg: %#04x, tc: %#04x, iid: %#04x, rc: %d)\n",
+		 ec ? "disabling" : "detaching", reg.target_category, id.target_category,
+		 id.instance, entry->refcount);
+
+	if (entry->flags != flags) {
+		ssam_warn(ctrl,
+			  "inconsistent flags when disabling event: got %#04x, expected %#04x (reg: %#04x, tc: %#04x, iid: %#04x)\n",
+			  flags, entry->flags, reg.target_category, id.target_category,
+			  id.instance);
+	}
+
+	if (ec && entry->refcount == 0) {
+		status = ssam_ssh_event_disable(ctrl, reg, id, flags);
+		kfree(entry);
+	}
+
+	return status;
+}
+
+/**
+ * ssam_notifier_register() - Register an event notifier.
+ * @ctrl: The controller to register the notifier on.
+ * @n:    The event notifier to register.
+ *
+ * Register an event notifier. Increment the usage counter of the associated
+ * SAM event if the notifier is not marked as an observer. If the event is not
+ * marked as an observer and is currently not enabled, it will be enabled
+ * during this call. If the notifier is marked as an observer, no attempt will
+ * be made at enabling any event and no reference count will be modified.
+ *
+ * Notifiers marked as observers do not need to be associated with one specific
+ * event, i.e. as long as no event matching is performed, only the event target
+ * category needs to be set.
+ *
+ * Return: Returns zero on success, %-ENOSPC if there have already been
+ * %INT_MAX notifiers for the event ID/type associated with the notifier block
+ * registered, %-ENOMEM if the corresponding event entry could not be
+ * allocated. If this is the first time that a notifier block is registered
+ * for the specific associated event, returns the status of the event-enable
+ * EC-command.
+ */
+int ssam_notifier_register(struct ssam_controller *ctrl, struct ssam_event_notifier *n)
+{
+	u16 rqid = ssh_tc_to_rqid(n->event.id.target_category);
+	struct ssam_nf_refcount_entry *entry = NULL;
+	struct ssam_nf_head *nf_head;
+	struct ssam_nf *nf;
+	int status;
+
+	if (!ssh_rqid_is_event(rqid))
+		return -EINVAL;
+
+	nf = &ctrl->cplt.event.notif;
+	nf_head = &nf->head[ssh_rqid_to_event(rqid)];
+
+	mutex_lock(&nf->lock);
+
+	if (!(n->flags & SSAM_EVENT_NOTIFIER_OBSERVER)) {
+		entry = ssam_nf_refcount_inc(nf, n->event.reg, n->event.id);
+		if (IS_ERR(entry)) {
+			mutex_unlock(&nf->lock);
+			return PTR_ERR(entry);
+		}
+	}
+
+	status = ssam_nfblk_insert(nf_head, &n->base);
+	if (status) {
+		if (entry)
+			ssam_nf_refcount_dec_free(nf, n->event.reg, n->event.id);
+
+		mutex_unlock(&nf->lock);
+		return status;
+	}
+
+	if (entry) {
+		status = ssam_nf_refcount_enable(ctrl, entry, n->event.flags);
+		if (status) {
+			ssam_nfblk_remove(&n->base);
+			ssam_nf_refcount_dec_free(nf, n->event.reg, n->event.id);
+			mutex_unlock(&nf->lock);
+			synchronize_srcu(&nf_head->srcu);
+			return status;
+		}
+	}
+
+	mutex_unlock(&nf->lock);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ssam_notifier_register);
+
+/**
+ * __ssam_notifier_unregister() - Unregister an event notifier.
+ * @ctrl:    The controller the notifier has been registered on.
+ * @n:       The event notifier to unregister.
+ * @disable: Whether to disable the corresponding event on the EC.
+ *
+ * Unregister an event notifier. Decrement the usage counter of the associated
+ * SAM event if the notifier is not marked as an observer. If the usage counter
+ * reaches zero and ``disable`` equals ``true``, the event will be disabled.
+ *
+ * Useful for hot-removable devices, where communication may fail once the
+ * device has been physically removed. In that case, specifying ``disable`` as
+ * ``false`` avoids communication with the EC.
+ *
+ * Return: Returns zero on success, %-ENOENT if the given notifier block has
+ * not been registered on the controller. If the given notifier block was the
+ * last one associated with its specific event, returns the status of the
+ * event-disable EC-command.
+ */
+int __ssam_notifier_unregister(struct ssam_controller *ctrl, struct ssam_event_notifier *n,
+			       bool disable)
+{
+	u16 rqid = ssh_tc_to_rqid(n->event.id.target_category);
+	struct ssam_nf_refcount_entry *entry;
+	struct ssam_nf_head *nf_head;
+	struct ssam_nf *nf;
+	int status = 0;
+
+	if (!ssh_rqid_is_event(rqid))
+		return -EINVAL;
+
+	nf = &ctrl->cplt.event.notif;
+	nf_head = &nf->head[ssh_rqid_to_event(rqid)];
+
+	mutex_lock(&nf->lock);
+
+	if (!ssam_nfblk_find(nf_head, &n->base)) {
+		mutex_unlock(&nf->lock);
+		return -ENOENT;
+	}
+
+	/*
+	 * If this is an observer notifier, do not attempt to disable the
+	 * event, just remove it.
+	 */
+	if (!(n->flags & SSAM_EVENT_NOTIFIER_OBSERVER)) {
+		entry = ssam_nf_refcount_dec(nf, n->event.reg, n->event.id);
+		if (WARN_ON(!entry)) {
+			/*
+			 * If this does not return an entry, there's a logic
+			 * error somewhere: The notifier block is registered,
+			 * but the event refcount entry is not there. Remove
+			 * the notifier block anyways.
+			 */
+			status = -ENOENT;
+			goto remove;
+		}
+
+		status = ssam_nf_refcount_disable_free(ctrl, entry, n->event.flags, disable);
+	}
+
+remove:
+	ssam_nfblk_remove(&n->base);
+	mutex_unlock(&nf->lock);
+	synchronize_srcu(&nf_head->srcu);
+
+	return status;
+}
+EXPORT_SYMBOL_GPL(__ssam_notifier_unregister);
+
+/**
+ * ssam_controller_event_enable() - Enable the specified event.
+ * @ctrl:  The controller to enable the event for.
+ * @reg:   The event registry to use for enabling the event.
+ * @id:    The event ID specifying the event to be enabled.
+ * @flags: The SAM event flags used for enabling the event.
+ *
+ * Increment the event reference count of the specified event. If the event has
+ * not been enabled previously, it will be enabled by this call.
+ *
+ * Note: In general, ssam_notifier_register() with a non-observer notifier
+ * should be preferred for enabling/disabling events, as this will guarantee
+ * proper ordering and event forwarding in case of errors during event
+ * enabling/disabling.
+ *
+ * Return: Returns zero on success, %-ENOSPC if the reference count for the
+ * specified event has reached its maximum, %-ENOMEM if the corresponding event
+ * entry could not be allocated. If this is the first time that this event has
+ * been enabled (i.e. the reference count was incremented from zero to one by
+ * this call), returns the status of the event-enable EC-command.
+ */
+int ssam_controller_event_enable(struct ssam_controller *ctrl,
+				 struct ssam_event_registry reg,
+				 struct ssam_event_id id, u8 flags)
+{
+	u16 rqid = ssh_tc_to_rqid(id.target_category);
+	struct ssam_nf *nf = &ctrl->cplt.event.notif;
+	struct ssam_nf_refcount_entry *entry;
+	int status;
+
+	if (!ssh_rqid_is_event(rqid))
+		return -EINVAL;
+
+	mutex_lock(&nf->lock);
+
+	entry = ssam_nf_refcount_inc(nf, reg, id);
+	if (IS_ERR(entry)) {
+		mutex_unlock(&nf->lock);
+		return PTR_ERR(entry);
+	}
+
+	status = ssam_nf_refcount_enable(ctrl, entry, flags);
+	if (status) {
+		ssam_nf_refcount_dec_free(nf, reg, id);
+		mutex_unlock(&nf->lock);
+		return status;
+	}
+
+	mutex_unlock(&nf->lock);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ssam_controller_event_enable);
+
+/**
+ * ssam_controller_event_disable() - Disable the specified event.
+ * @ctrl:  The controller to disable the event for.
+ * @reg:   The event registry to use for disabling the event.
+ * @id:    The event ID specifying the event to be disabled.
+ * @flags: The flags used when enabling the event.
+ *
+ * Decrement the reference count of the specified event. If the reference count
+ * reaches zero, the event will be disabled.
+ *
+ * Note: In general, ssam_notifier_register()/ssam_notifier_unregister() with a
+ * non-observer notifier should be preferred for enabling/disabling events, as
+ * this will guarantee proper ordering and event forwarding in case of errors
+ * during event enabling/disabling.
+ *
+ * Return: Returns zero on success, %-ENOENT if the given event has not been
+ * enabled on the controller. If the reference count of the event reaches zero
+ * during this call, returns the status of the event-disable EC-command.
+ */
+int ssam_controller_event_disable(struct ssam_controller *ctrl,
+				  struct ssam_event_registry reg,
+				  struct ssam_event_id id, u8 flags)
+{
+	u16 rqid = ssh_tc_to_rqid(id.target_category);
+	struct ssam_nf *nf = &ctrl->cplt.event.notif;
+	struct ssam_nf_refcount_entry *entry;
+	int status;
+
+	if (!ssh_rqid_is_event(rqid))
+		return -EINVAL;
+
+	mutex_lock(&nf->lock);
+
+	entry = ssam_nf_refcount_dec(nf, reg, id);
+	if (!entry) {
+		mutex_unlock(&nf->lock);
+		return -ENOENT;
+	}
+
+	status = ssam_nf_refcount_disable_free(ctrl, entry, flags, true);
+
+	mutex_unlock(&nf->lock);
+	return status;
+}
+EXPORT_SYMBOL_GPL(ssam_controller_event_disable);
+
+/**
+ * ssam_notifier_disable_registered() - Disable events for all registered
+ * notifiers.
+ * @ctrl: The controller for which to disable the notifiers/events.
+ *
+ * Disables events for all currently registered notifiers. In case of an error
+ * (EC command failing), all previously disabled events will be restored and
+ * the error code returned.
+ *
+ * This function is intended to disable all events prior to hibernation entry.
+ * See ssam_notifier_restore_registered() to restore/re-enable all events
+ * disabled with this function.
+ *
+ * Note that this function will not disable events for notifiers registered
+ * after calling this function. It should thus be made sure that no new
+ * notifiers are going to be added after this call and before the corresponding
+ * call to ssam_notifier_restore_registered().
+ *
+ * Return: Returns zero on success. In case of failure returns the error code
+ * returned by the failed EC command to disable an event.
+ */
+int ssam_notifier_disable_registered(struct ssam_controller *ctrl)
+{
+	struct ssam_nf *nf = &ctrl->cplt.event.notif;
+	struct rb_node *n;
+	int status;
+
+	mutex_lock(&nf->lock);
+	for (n = rb_first(&nf->refcount); n; n = rb_next(n)) {
+		struct ssam_nf_refcount_entry *e;
+
+		e = rb_entry(n, struct ssam_nf_refcount_entry, node);
+		status = ssam_ssh_event_disable(ctrl, e->key.reg,
+						e->key.id, e->flags);
+		if (status)
+			goto err;
+	}
+	mutex_unlock(&nf->lock);
+
+	return 0;
+
+err:
+	for (n = rb_prev(n); n; n = rb_prev(n)) {
+		struct ssam_nf_refcount_entry *e;
+
+		e = rb_entry(n, struct ssam_nf_refcount_entry, node);
+		ssam_ssh_event_enable(ctrl, e->key.reg, e->key.id, e->flags);
+	}
+	mutex_unlock(&nf->lock);
+
+	return status;
+}
+
+/**
+ * ssam_notifier_restore_registered() - Restore/re-enable events for all
+ * registered notifiers.
+ * @ctrl: The controller for which to restore the notifiers/events.
+ *
+ * Restores/re-enables all events for which notifiers have been registered on
+ * the given controller. In case of a failure, the error is logged and the
+ * function continues to try and enable the remaining events.
+ *
+ * This function is intended to restore/re-enable all registered events after
+ * hibernation. See ssam_notifier_disable_registered() for the counter part
+ * disabling the events and more details.
+ */
+void ssam_notifier_restore_registered(struct ssam_controller *ctrl)
+{
+	struct ssam_nf *nf = &ctrl->cplt.event.notif;
+	struct rb_node *n;
+
+	mutex_lock(&nf->lock);
+	for (n = rb_first(&nf->refcount); n; n = rb_next(n)) {
+		struct ssam_nf_refcount_entry *e;
+
+		e = rb_entry(n, struct ssam_nf_refcount_entry, node);
+
+		/* Ignore errors, will get logged in call. */
+		ssam_ssh_event_enable(ctrl, e->key.reg, e->key.id, e->flags);
+	}
+	mutex_unlock(&nf->lock);
+}
+
+/**
+ * ssam_notifier_is_empty() - Check if there are any registered notifiers.
+ * @ctrl: The controller to check on.
+ *
+ * Return: Returns %true if there are currently no notifiers registered on the
+ * controller, %false otherwise.
+ */
+static bool ssam_notifier_is_empty(struct ssam_controller *ctrl)
+{
+	struct ssam_nf *nf = &ctrl->cplt.event.notif;
+	bool result;
+
+	mutex_lock(&nf->lock);
+	result = ssam_nf_refcount_empty(nf);
+	mutex_unlock(&nf->lock);
+
+	return result;
+}
+
+/**
+ * ssam_notifier_unregister_all() - Unregister all currently registered
+ * notifiers.
+ * @ctrl: The controller to unregister the notifiers on.
+ *
+ * Unregisters all currently registered notifiers. This function is used to
+ * ensure that all notifiers will be unregistered and associated
+ * entries/resources freed when the controller is being shut down.
+ */
+static void ssam_notifier_unregister_all(struct ssam_controller *ctrl)
+{
+	struct ssam_nf *nf = &ctrl->cplt.event.notif;
+	struct ssam_nf_refcount_entry *e, *n;
+
+	mutex_lock(&nf->lock);
+	rbtree_postorder_for_each_entry_safe(e, n, &nf->refcount, node) {
+		/* Ignore errors, will get logged in call. */
+		ssam_ssh_event_disable(ctrl, e->key.reg, e->key.id, e->flags);
+		kfree(e);
+	}
+	nf->refcount = RB_ROOT;
+	mutex_unlock(&nf->lock);
+}
+
+
+/* -- Wakeup IRQ. ----------------------------------------------------------- */
+
+static irqreturn_t ssam_irq_handle(int irq, void *dev_id)
+{
+	struct ssam_controller *ctrl = dev_id;
+
+	ssam_dbg(ctrl, "pm: wake irq triggered\n");
+
+	/*
+	 * Note: Proper wakeup detection is currently unimplemented.
+	 *       When the EC is in display-off or any other non-D0 state, it
+	 *       does not send events/notifications to the host. Instead it
+	 *       signals that there are events available via the wakeup IRQ.
+	 *       This driver is responsible for calling back to the EC to
+	 *       release these events one-by-one.
+	 *
+	 *       This IRQ should not cause a full system resume by its own.
+	 *       Instead, events should be handled by their respective subsystem
+	 *       drivers, which in turn should signal whether a full system
+	 *       resume should be performed.
+	 *
+	 * TODO: Send GPIO callback command repeatedly to EC until callback
+	 *       returns 0x00. Return flag of callback is "has more events".
+	 *       Each time the command is sent, one event is "released". Once
+	 *       all events have been released (return = 0x00), the GPIO is
+	 *       re-armed. Detect wakeup events during this process, go back to
+	 *       sleep if no wakeup event has been received.
+	 */
+
+	return IRQ_HANDLED;
+}
+
+/**
+ * ssam_irq_setup() - Set up SAM EC wakeup-GPIO interrupt.
+ * @ctrl: The controller for which the IRQ should be set up.
+ *
+ * Set up an IRQ for the wakeup-GPIO pin of the SAM EC. This IRQ can be used
+ * to wake the device from a low power state.
+ *
+ * Note that this IRQ can only be triggered while the EC is in the display-off
+ * state. In this state, events are not sent to the host in the usual way.
+ * Instead the wakeup-GPIO gets pulled to "high" as long as there are pending
+ * events and these events need to be released one-by-one via the GPIO
+ * callback request, either until there are no events left and the GPIO is
+ * reset, or all at once by transitioning the EC out of the display-off state,
+ * which will also clear the GPIO.
+ *
+ * Not all events, however, should trigger a full system wakeup. Instead the
+ * driver should, if necessary, inspect and forward each event to the
+ * corresponding subsystem, which in turn should decide if the system needs to
+ * be woken up. This logic has not been implemented yet, thus wakeup by this
+ * IRQ should be disabled by default to avoid spurious wake-ups, caused, for
+ * example, by the remaining battery percentage changing. Refer to comments in
+ * this function and comments in the corresponding IRQ handler for more
+ * details on how this should be implemented.
+ *
+ * See also ssam_ctrl_notif_display_off() and ssam_ctrl_notif_display_off()
+ * for functions to transition the EC into and out of the display-off state as
+ * well as more details on it.
+ *
+ * The IRQ is disabled by default and has to be enabled before it can wake up
+ * the device from suspend via ssam_irq_arm_for_wakeup(). On teardown, the IRQ
+ * should be freed via ssam_irq_free().
+ */
+int ssam_irq_setup(struct ssam_controller *ctrl)
+{
+	struct device *dev = ssam_controller_device(ctrl);
+	struct gpio_desc *gpiod;
+	int irq;
+	int status;
+
+	/*
+	 * The actual GPIO interrupt is declared in ACPI as TRIGGER_HIGH.
+	 * However, the GPIO line only gets reset by sending the GPIO callback
+	 * command to SAM (or alternatively the display-on notification). As
+	 * proper handling for this interrupt is not implemented yet, leaving
+	 * the IRQ at TRIGGER_HIGH would cause an IRQ storm (as the callback
+	 * never gets sent and thus the line never gets reset). To avoid this,
+	 * mark the IRQ as TRIGGER_RISING for now, only creating a single
+	 * interrupt, and let the SAM resume callback during the controller
+	 * resume process clear it.
+	 */
+	const int irqf = IRQF_ONESHOT | IRQF_TRIGGER_RISING | IRQF_NO_AUTOEN;
+
+	gpiod = gpiod_get(dev, "ssam_wakeup-int", GPIOD_ASIS);
+	if (IS_ERR(gpiod))
+		return PTR_ERR(gpiod);
+
+	irq = gpiod_to_irq(gpiod);
+	gpiod_put(gpiod);
+
+	if (irq < 0)
+		return irq;
+
+	status = request_threaded_irq(irq, NULL, ssam_irq_handle, irqf,
+				      "ssam_wakeup", ctrl);
+	if (status)
+		return status;
+
+	ctrl->irq.num = irq;
+	return 0;
+}
+
+/**
+ * ssam_irq_free() - Free SAM EC wakeup-GPIO interrupt.
+ * @ctrl: The controller for which the IRQ should be freed.
+ *
+ * Free the wakeup-GPIO IRQ previously set-up via ssam_irq_setup().
+ */
+void ssam_irq_free(struct ssam_controller *ctrl)
+{
+	free_irq(ctrl->irq.num, ctrl);
+	ctrl->irq.num = -1;
+}
+
+/**
+ * ssam_irq_arm_for_wakeup() - Arm the EC IRQ for wakeup, if enabled.
+ * @ctrl: The controller for which the IRQ should be armed.
+ *
+ * Sets up the IRQ so that it can be used to wake the device. Specifically,
+ * this function enables the irq and then, if the device is allowed to wake up
+ * the system, calls enable_irq_wake(). See ssam_irq_disarm_wakeup() for the
+ * corresponding function to disable the IRQ.
+ *
+ * This function is intended to arm the IRQ before entering S2idle suspend.
+ *
+ * Note: calls to ssam_irq_arm_for_wakeup() and ssam_irq_disarm_wakeup() must
+ * be balanced.
+ */
+int ssam_irq_arm_for_wakeup(struct ssam_controller *ctrl)
+{
+	struct device *dev = ssam_controller_device(ctrl);
+	int status;
+
+	enable_irq(ctrl->irq.num);
+	if (device_may_wakeup(dev)) {
+		status = enable_irq_wake(ctrl->irq.num);
+		if (status) {
+			ssam_err(ctrl, "failed to enable wake IRQ: %d\n", status);
+			disable_irq(ctrl->irq.num);
+			return status;
+		}
+
+		ctrl->irq.wakeup_enabled = true;
+	} else {
+		ctrl->irq.wakeup_enabled = false;
+	}
+
+	return 0;
+}
+
+/**
+ * ssam_irq_disarm_wakeup() - Disarm the wakeup IRQ.
+ * @ctrl: The controller for which the IRQ should be disarmed.
+ *
+ * Disarm the IRQ previously set up for wake via ssam_irq_arm_for_wakeup().
+ *
+ * This function is intended to disarm the IRQ after exiting S2idle suspend.
+ *
+ * Note: calls to ssam_irq_arm_for_wakeup() and ssam_irq_disarm_wakeup() must
+ * be balanced.
+ */
+void ssam_irq_disarm_wakeup(struct ssam_controller *ctrl)
+{
+	int status;
+
+	if (ctrl->irq.wakeup_enabled) {
+		status = disable_irq_wake(ctrl->irq.num);
+		if (status)
+			ssam_err(ctrl, "failed to disable wake IRQ: %d\n", status);
+
+		ctrl->irq.wakeup_enabled = false;
+	}
+	disable_irq(ctrl->irq.num);
+}
diff --git a/drivers/platform/surface/aggregator/controller.h b/drivers/platform/surface/aggregator/controller.h
new file mode 100644
index 000000000..f0d987abc
--- /dev/null
+++ b/drivers/platform/surface/aggregator/controller.h
@@ -0,0 +1,285 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Main SSAM/SSH controller structure and functionality.
+ *
+ * Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#ifndef _SURFACE_AGGREGATOR_CONTROLLER_H
+#define _SURFACE_AGGREGATOR_CONTROLLER_H
+
+#include <linux/kref.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/rbtree.h>
+#include <linux/rwsem.h>
+#include <linux/serdev.h>
+#include <linux/spinlock.h>
+#include <linux/srcu.h>
+#include <linux/types.h>
+#include <linux/workqueue.h>
+
+#include <linux/surface_aggregator/controller.h>
+#include <linux/surface_aggregator/serial_hub.h>
+
+#include "ssh_request_layer.h"
+
+
+/* -- Safe counters. -------------------------------------------------------- */
+
+/**
+ * struct ssh_seq_counter - Safe counter for SSH sequence IDs.
+ * @value: The current counter value.
+ */
+struct ssh_seq_counter {
+	u8 value;
+};
+
+/**
+ * struct ssh_rqid_counter - Safe counter for SSH request IDs.
+ * @value: The current counter value.
+ */
+struct ssh_rqid_counter {
+	u16 value;
+};
+
+
+/* -- Event/notification system. -------------------------------------------- */
+
+/**
+ * struct ssam_nf_head - Notifier head for SSAM events.
+ * @srcu: The SRCU struct for synchronization.
+ * @head: List-head for notifier blocks registered under this head.
+ */
+struct ssam_nf_head {
+	struct srcu_struct srcu;
+	struct list_head head;
+};
+
+/**
+ * struct ssam_nf - Notifier callback- and activation-registry for SSAM events.
+ * @lock:     Lock guarding (de-)registration of notifier blocks. Note: This
+ *            lock does not need to be held for notifier calls, only
+ *            registration and deregistration.
+ * @refcount: The root of the RB-tree used for reference-counting enabled
+ *            events/notifications.
+ * @head:     The list of notifier heads for event/notification callbacks.
+ */
+struct ssam_nf {
+	struct mutex lock;
+	struct rb_root refcount;
+	struct ssam_nf_head head[SSH_NUM_EVENTS];
+};
+
+
+/* -- Event/async request completion system. -------------------------------- */
+
+struct ssam_cplt;
+
+/**
+ * struct ssam_event_item - Struct for event queuing and completion.
+ * @node:     The node in the queue.
+ * @rqid:     The request ID of the event.
+ * @ops:      Instance specific functions.
+ * @ops.free: Callback for freeing this event item.
+ * @event:    Actual event data.
+ */
+struct ssam_event_item {
+	struct list_head node;
+	u16 rqid;
+
+	struct {
+		void (*free)(struct ssam_event_item *event);
+	} ops;
+
+	struct ssam_event event;	/* must be last */
+};
+
+/**
+ * struct ssam_event_queue - Queue for completing received events.
+ * @cplt: Reference to the completion system on which this queue is active.
+ * @lock: The lock for any operation on the queue.
+ * @head: The list-head of the queue.
+ * @work: The &struct work_struct performing completion work for this queue.
+ */
+struct ssam_event_queue {
+	struct ssam_cplt *cplt;
+
+	spinlock_t lock;
+	struct list_head head;
+	struct work_struct work;
+};
+
+/**
+ * struct ssam_event_target - Set of queues for a single SSH target ID.
+ * @queue: The array of queues, one queue per event ID.
+ */
+struct ssam_event_target {
+	struct ssam_event_queue queue[SSH_NUM_EVENTS];
+};
+
+/**
+ * struct ssam_cplt - SSAM event/async request completion system.
+ * @dev:          The device with which this system is associated. Only used
+ *                for logging.
+ * @wq:           The &struct workqueue_struct on which all completion work
+ *                items are queued.
+ * @event:        Event completion management.
+ * @event.target: Array of &struct ssam_event_target, one for each target.
+ * @event.notif:  Notifier callbacks and event activation reference counting.
+ */
+struct ssam_cplt {
+	struct device *dev;
+	struct workqueue_struct *wq;
+
+	struct {
+		struct ssam_event_target target[SSH_NUM_TARGETS];
+		struct ssam_nf notif;
+	} event;
+};
+
+
+/* -- Main SSAM device structures. ------------------------------------------ */
+
+/**
+ * enum ssam_controller_state - State values for &struct ssam_controller.
+ * @SSAM_CONTROLLER_UNINITIALIZED:
+ *	The controller has not been initialized yet or has been deinitialized.
+ * @SSAM_CONTROLLER_INITIALIZED:
+ *	The controller is initialized, but has not been started yet.
+ * @SSAM_CONTROLLER_STARTED:
+ *	The controller has been started and is ready to use.
+ * @SSAM_CONTROLLER_STOPPED:
+ *	The controller has been stopped.
+ * @SSAM_CONTROLLER_SUSPENDED:
+ *	The controller has been suspended.
+ */
+enum ssam_controller_state {
+	SSAM_CONTROLLER_UNINITIALIZED,
+	SSAM_CONTROLLER_INITIALIZED,
+	SSAM_CONTROLLER_STARTED,
+	SSAM_CONTROLLER_STOPPED,
+	SSAM_CONTROLLER_SUSPENDED,
+};
+
+/**
+ * struct ssam_controller_caps - Controller device capabilities.
+ * @ssh_power_profile:             SSH power profile.
+ * @ssh_buffer_size:               SSH driver UART buffer size.
+ * @screen_on_sleep_idle_timeout:  SAM UART screen-on sleep idle timeout.
+ * @screen_off_sleep_idle_timeout: SAM UART screen-off sleep idle timeout.
+ * @d3_closes_handle:              SAM closes UART handle in D3.
+ *
+ * Controller and SSH device capabilities found in ACPI.
+ */
+struct ssam_controller_caps {
+	u32 ssh_power_profile;
+	u32 ssh_buffer_size;
+	u32 screen_on_sleep_idle_timeout;
+	u32 screen_off_sleep_idle_timeout;
+	u32 d3_closes_handle:1;
+};
+
+/**
+ * struct ssam_controller - SSAM controller device.
+ * @kref:  Reference count of the controller.
+ * @lock:  Main lock for the controller, used to guard state changes.
+ * @state: Controller state.
+ * @rtl:   Request transport layer for SSH I/O.
+ * @cplt:  Completion system for SSH/SSAM events and asynchronous requests.
+ * @counter:      Safe SSH message ID counters.
+ * @counter.seq:  Sequence ID counter.
+ * @counter.rqid: Request ID counter.
+ * @irq:          Wakeup IRQ resources.
+ * @irq.num:      The wakeup IRQ number.
+ * @irq.wakeup_enabled: Whether wakeup by IRQ is enabled during suspend.
+ * @caps: The controller device capabilities.
+ */
+struct ssam_controller {
+	struct kref kref;
+
+	struct rw_semaphore lock;
+	enum ssam_controller_state state;
+
+	struct ssh_rtl rtl;
+	struct ssam_cplt cplt;
+
+	struct {
+		struct ssh_seq_counter seq;
+		struct ssh_rqid_counter rqid;
+	} counter;
+
+	struct {
+		int num;
+		bool wakeup_enabled;
+	} irq;
+
+	struct ssam_controller_caps caps;
+};
+
+#define to_ssam_controller(ptr, member) \
+	container_of(ptr, struct ssam_controller, member)
+
+#define ssam_dbg(ctrl, fmt, ...)  rtl_dbg(&(ctrl)->rtl, fmt, ##__VA_ARGS__)
+#define ssam_info(ctrl, fmt, ...) rtl_info(&(ctrl)->rtl, fmt, ##__VA_ARGS__)
+#define ssam_warn(ctrl, fmt, ...) rtl_warn(&(ctrl)->rtl, fmt, ##__VA_ARGS__)
+#define ssam_err(ctrl, fmt, ...)  rtl_err(&(ctrl)->rtl, fmt, ##__VA_ARGS__)
+
+/**
+ * ssam_controller_receive_buf() - Provide input-data to the controller.
+ * @ctrl: The controller.
+ * @buf:  The input buffer.
+ * @n:    The number of bytes in the input buffer.
+ *
+ * Provide input data to be evaluated by the controller, which has been
+ * received via the lower-level transport.
+ *
+ * Return: Returns the number of bytes consumed, or, if the packet transport
+ * layer of the controller has been shut down, %-ESHUTDOWN.
+ */
+static inline
+int ssam_controller_receive_buf(struct ssam_controller *ctrl,
+				const unsigned char *buf, size_t n)
+{
+	return ssh_ptl_rx_rcvbuf(&ctrl->rtl.ptl, buf, n);
+}
+
+/**
+ * ssam_controller_write_wakeup() - Notify the controller that the underlying
+ * device has space available for data to be written.
+ * @ctrl: The controller.
+ */
+static inline void ssam_controller_write_wakeup(struct ssam_controller *ctrl)
+{
+	ssh_ptl_tx_wakeup_transfer(&ctrl->rtl.ptl);
+}
+
+int ssam_controller_init(struct ssam_controller *ctrl, struct serdev_device *s);
+int ssam_controller_start(struct ssam_controller *ctrl);
+void ssam_controller_shutdown(struct ssam_controller *ctrl);
+void ssam_controller_destroy(struct ssam_controller *ctrl);
+
+int ssam_notifier_disable_registered(struct ssam_controller *ctrl);
+void ssam_notifier_restore_registered(struct ssam_controller *ctrl);
+
+int ssam_irq_setup(struct ssam_controller *ctrl);
+void ssam_irq_free(struct ssam_controller *ctrl);
+int ssam_irq_arm_for_wakeup(struct ssam_controller *ctrl);
+void ssam_irq_disarm_wakeup(struct ssam_controller *ctrl);
+
+void ssam_controller_lock(struct ssam_controller *c);
+void ssam_controller_unlock(struct ssam_controller *c);
+
+int ssam_get_firmware_version(struct ssam_controller *ctrl, u32 *version);
+int ssam_ctrl_notif_display_off(struct ssam_controller *ctrl);
+int ssam_ctrl_notif_display_on(struct ssam_controller *ctrl);
+int ssam_ctrl_notif_d0_exit(struct ssam_controller *ctrl);
+int ssam_ctrl_notif_d0_entry(struct ssam_controller *ctrl);
+
+int ssam_controller_suspend(struct ssam_controller *ctrl);
+int ssam_controller_resume(struct ssam_controller *ctrl);
+
+int ssam_event_item_cache_init(void);
+void ssam_event_item_cache_destroy(void);
+
+#endif /* _SURFACE_AGGREGATOR_CONTROLLER_H */
diff --git a/drivers/platform/surface/aggregator/core.c b/drivers/platform/surface/aggregator/core.c
new file mode 100644
index 000000000..6152be383
--- /dev/null
+++ b/drivers/platform/surface/aggregator/core.c
@@ -0,0 +1,836 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Surface Serial Hub (SSH) driver for communication with the Surface/System
+ * Aggregator Module (SSAM/SAM).
+ *
+ * Provides access to a SAM-over-SSH connected EC via a controller device.
+ * Handles communication via requests as well as enabling, disabling, and
+ * relaying of events.
+ *
+ * Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#include <linux/acpi.h>
+#include <linux/atomic.h>
+#include <linux/completion.h>
+#include <linux/gpio/consumer.h>
+#include <linux/kernel.h>
+#include <linux/kref.h>
+#include <linux/module.h>
+#include <linux/pm.h>
+#include <linux/serdev.h>
+#include <linux/sysfs.h>
+
+#include <linux/surface_aggregator/controller.h>
+#include <linux/surface_aggregator/device.h>
+
+#include "bus.h"
+#include "controller.h"
+
+#define CREATE_TRACE_POINTS
+#include "trace.h"
+
+
+/* -- Static controller reference. ------------------------------------------ */
+
+/*
+ * Main controller reference. The corresponding lock must be held while
+ * accessing (reading/writing) the reference.
+ */
+static struct ssam_controller *__ssam_controller;
+static DEFINE_SPINLOCK(__ssam_controller_lock);
+
+/**
+ * ssam_get_controller() - Get reference to SSAM controller.
+ *
+ * Returns a reference to the SSAM controller of the system or %NULL if there
+ * is none, it hasn't been set up yet, or it has already been unregistered.
+ * This function automatically increments the reference count of the
+ * controller, thus the calling party must ensure that ssam_controller_put()
+ * is called when it doesn't need the controller any more.
+ */
+struct ssam_controller *ssam_get_controller(void)
+{
+	struct ssam_controller *ctrl;
+
+	spin_lock(&__ssam_controller_lock);
+
+	ctrl = __ssam_controller;
+	if (!ctrl)
+		goto out;
+
+	if (WARN_ON(!kref_get_unless_zero(&ctrl->kref)))
+		ctrl = NULL;
+
+out:
+	spin_unlock(&__ssam_controller_lock);
+	return ctrl;
+}
+EXPORT_SYMBOL_GPL(ssam_get_controller);
+
+/**
+ * ssam_try_set_controller() - Try to set the main controller reference.
+ * @ctrl: The controller to which the reference should point.
+ *
+ * Set the main controller reference to the given pointer if the reference
+ * hasn't been set already.
+ *
+ * Return: Returns zero on success or %-EEXIST if the reference has already
+ * been set.
+ */
+static int ssam_try_set_controller(struct ssam_controller *ctrl)
+{
+	int status = 0;
+
+	spin_lock(&__ssam_controller_lock);
+	if (!__ssam_controller)
+		__ssam_controller = ctrl;
+	else
+		status = -EEXIST;
+	spin_unlock(&__ssam_controller_lock);
+
+	return status;
+}
+
+/**
+ * ssam_clear_controller() - Remove/clear the main controller reference.
+ *
+ * Clears the main controller reference, i.e. sets it to %NULL. This function
+ * should be called before the controller is shut down.
+ */
+static void ssam_clear_controller(void)
+{
+	spin_lock(&__ssam_controller_lock);
+	__ssam_controller = NULL;
+	spin_unlock(&__ssam_controller_lock);
+}
+
+/**
+ * ssam_client_link() - Link an arbitrary client device to the controller.
+ * @c: The controller to link to.
+ * @client: The client device.
+ *
+ * Link an arbitrary client device to the controller by creating a device link
+ * between it as consumer and the controller device as provider. This function
+ * can be used for non-SSAM devices (or SSAM devices not registered as child
+ * under the controller) to guarantee that the controller is valid for as long
+ * as the driver of the client device is bound, and that proper suspend and
+ * resume ordering is guaranteed.
+ *
+ * The device link does not have to be destructed manually. It is removed
+ * automatically once the driver of the client device unbinds.
+ *
+ * Return: Returns zero on success, %-ENODEV if the controller is not ready or
+ * going to be removed soon, or %-ENOMEM if the device link could not be
+ * created for other reasons.
+ */
+int ssam_client_link(struct ssam_controller *c, struct device *client)
+{
+	const u32 flags = DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
+	struct device_link *link;
+	struct device *ctrldev;
+
+	ssam_controller_statelock(c);
+
+	if (c->state != SSAM_CONTROLLER_STARTED) {
+		ssam_controller_stateunlock(c);
+		return -ENODEV;
+	}
+
+	ctrldev = ssam_controller_device(c);
+	if (!ctrldev) {
+		ssam_controller_stateunlock(c);
+		return -ENODEV;
+	}
+
+	link = device_link_add(client, ctrldev, flags);
+	if (!link) {
+		ssam_controller_stateunlock(c);
+		return -ENOMEM;
+	}
+
+	/*
+	 * Return -ENODEV if supplier driver is on its way to be removed. In
+	 * this case, the controller won't be around for much longer and the
+	 * device link is not going to save us any more, as unbinding is
+	 * already in progress.
+	 */
+	if (READ_ONCE(link->status) == DL_STATE_SUPPLIER_UNBIND) {
+		ssam_controller_stateunlock(c);
+		return -ENODEV;
+	}
+
+	ssam_controller_stateunlock(c);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ssam_client_link);
+
+/**
+ * ssam_client_bind() - Bind an arbitrary client device to the controller.
+ * @client: The client device.
+ *
+ * Link an arbitrary client device to the controller by creating a device link
+ * between it as consumer and the main controller device as provider. This
+ * function can be used for non-SSAM devices to guarantee that the controller
+ * returned by this function is valid for as long as the driver of the client
+ * device is bound, and that proper suspend and resume ordering is guaranteed.
+ *
+ * This function does essentially the same as ssam_client_link(), except that
+ * it first fetches the main controller reference, then creates the link, and
+ * finally returns this reference. Note that this function does not increment
+ * the reference counter of the controller, as, due to the link, the
+ * controller lifetime is assured as long as the driver of the client device
+ * is bound.
+ *
+ * It is not valid to use the controller reference obtained by this method
+ * outside of the driver bound to the client device at the time of calling
+ * this function, without first incrementing the reference count of the
+ * controller via ssam_controller_get(). Even after doing this, care must be
+ * taken that requests are only submitted and notifiers are only
+ * (un-)registered when the controller is active and not suspended. In other
+ * words: The device link only lives as long as the client driver is bound and
+ * any guarantees enforced by this link (e.g. active controller state) can
+ * only be relied upon as long as this link exists and may need to be enforced
+ * in other ways afterwards.
+ *
+ * The created device link does not have to be destructed manually. It is
+ * removed automatically once the driver of the client device unbinds.
+ *
+ * Return: Returns the controller on success, an error pointer with %-ENODEV
+ * if the controller is not present, not ready or going to be removed soon, or
+ * %-ENOMEM if the device link could not be created for other reasons.
+ */
+struct ssam_controller *ssam_client_bind(struct device *client)
+{
+	struct ssam_controller *c;
+	int status;
+
+	c = ssam_get_controller();
+	if (!c)
+		return ERR_PTR(-ENODEV);
+
+	status = ssam_client_link(c, client);
+
+	/*
+	 * Note that we can drop our controller reference in both success and
+	 * failure cases: On success, we have bound the controller lifetime
+	 * inherently to the client driver lifetime, i.e. it the controller is
+	 * now guaranteed to outlive the client driver. On failure, we're not
+	 * going to use the controller any more.
+	 */
+	ssam_controller_put(c);
+
+	return status >= 0 ? c : ERR_PTR(status);
+}
+EXPORT_SYMBOL_GPL(ssam_client_bind);
+
+
+/* -- Glue layer (serdev_device -> ssam_controller). ------------------------ */
+
+static int ssam_receive_buf(struct serdev_device *dev, const unsigned char *buf,
+			    size_t n)
+{
+	struct ssam_controller *ctrl;
+	int ret;
+
+	ctrl = serdev_device_get_drvdata(dev);
+	ret = ssam_controller_receive_buf(ctrl, buf, n);
+
+	return ret < 0 ? 0 : ret;
+}
+
+static void ssam_write_wakeup(struct serdev_device *dev)
+{
+	ssam_controller_write_wakeup(serdev_device_get_drvdata(dev));
+}
+
+static const struct serdev_device_ops ssam_serdev_ops = {
+	.receive_buf = ssam_receive_buf,
+	.write_wakeup = ssam_write_wakeup,
+};
+
+
+/* -- SysFS and misc. ------------------------------------------------------- */
+
+static int ssam_log_firmware_version(struct ssam_controller *ctrl)
+{
+	u32 version, a, b, c;
+	int status;
+
+	status = ssam_get_firmware_version(ctrl, &version);
+	if (status)
+		return status;
+
+	a = (version >> 24) & 0xff;
+	b = ((version >> 8) & 0xffff);
+	c = version & 0xff;
+
+	ssam_info(ctrl, "SAM firmware version: %u.%u.%u\n", a, b, c);
+	return 0;
+}
+
+static ssize_t firmware_version_show(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	struct ssam_controller *ctrl = dev_get_drvdata(dev);
+	u32 version, a, b, c;
+	int status;
+
+	status = ssam_get_firmware_version(ctrl, &version);
+	if (status < 0)
+		return status;
+
+	a = (version >> 24) & 0xff;
+	b = ((version >> 8) & 0xffff);
+	c = version & 0xff;
+
+	return sysfs_emit(buf, "%u.%u.%u\n", a, b, c);
+}
+static DEVICE_ATTR_RO(firmware_version);
+
+static struct attribute *ssam_sam_attrs[] = {
+	&dev_attr_firmware_version.attr,
+	NULL
+};
+
+static const struct attribute_group ssam_sam_group = {
+	.name = "sam",
+	.attrs = ssam_sam_attrs,
+};
+
+
+/* -- ACPI based device setup. ---------------------------------------------- */
+
+static acpi_status ssam_serdev_setup_via_acpi_crs(struct acpi_resource *rsc,
+						  void *ctx)
+{
+	struct serdev_device *serdev = ctx;
+	struct acpi_resource_uart_serialbus *uart;
+	bool flow_control;
+	int status = 0;
+
+	if (!serdev_acpi_get_uart_resource(rsc, &uart))
+		return AE_OK;
+
+	/* Set up serdev device. */
+	serdev_device_set_baudrate(serdev, uart->default_baud_rate);
+
+	/* serdev currently only supports RTSCTS flow control. */
+	if (uart->flow_control & (~((u8)ACPI_UART_FLOW_CONTROL_HW))) {
+		dev_warn(&serdev->dev, "setup: unsupported flow control (value: %#04x)\n",
+			 uart->flow_control);
+	}
+
+	/* Set RTSCTS flow control. */
+	flow_control = uart->flow_control & ACPI_UART_FLOW_CONTROL_HW;
+	serdev_device_set_flow_control(serdev, flow_control);
+
+	/* serdev currently only supports EVEN/ODD parity. */
+	switch (uart->parity) {
+	case ACPI_UART_PARITY_NONE:
+		status = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
+		break;
+	case ACPI_UART_PARITY_EVEN:
+		status = serdev_device_set_parity(serdev, SERDEV_PARITY_EVEN);
+		break;
+	case ACPI_UART_PARITY_ODD:
+		status = serdev_device_set_parity(serdev, SERDEV_PARITY_ODD);
+		break;
+	default:
+		dev_warn(&serdev->dev, "setup: unsupported parity (value: %#04x)\n",
+			 uart->parity);
+		break;
+	}
+
+	if (status) {
+		dev_err(&serdev->dev, "setup: failed to set parity (value: %#04x, error: %d)\n",
+			uart->parity, status);
+		return AE_ERROR;
+	}
+
+	/* We've found the resource and are done. */
+	return AE_CTRL_TERMINATE;
+}
+
+static acpi_status ssam_serdev_setup_via_acpi(acpi_handle handle,
+					      struct serdev_device *serdev)
+{
+	return acpi_walk_resources(handle, METHOD_NAME__CRS,
+				   ssam_serdev_setup_via_acpi_crs, serdev);
+}
+
+
+/* -- Power management. ----------------------------------------------------- */
+
+static void ssam_serial_hub_shutdown(struct device *dev)
+{
+	struct ssam_controller *c = dev_get_drvdata(dev);
+	int status;
+
+	/*
+	 * Try to disable notifiers, signal display-off and D0-exit, ignore any
+	 * errors.
+	 *
+	 * Note: It has not been established yet if this is actually
+	 * necessary/useful for shutdown.
+	 */
+
+	status = ssam_notifier_disable_registered(c);
+	if (status) {
+		ssam_err(c, "pm: failed to disable notifiers for shutdown: %d\n",
+			 status);
+	}
+
+	status = ssam_ctrl_notif_display_off(c);
+	if (status)
+		ssam_err(c, "pm: display-off notification failed: %d\n", status);
+
+	status = ssam_ctrl_notif_d0_exit(c);
+	if (status)
+		ssam_err(c, "pm: D0-exit notification failed: %d\n", status);
+}
+
+#ifdef CONFIG_PM_SLEEP
+
+static int ssam_serial_hub_pm_prepare(struct device *dev)
+{
+	struct ssam_controller *c = dev_get_drvdata(dev);
+	int status;
+
+	/*
+	 * Try to signal display-off, This will quiesce events.
+	 *
+	 * Note: Signaling display-off/display-on should normally be done from
+	 * some sort of display state notifier. As that is not available,
+	 * signal it here.
+	 */
+
+	status = ssam_ctrl_notif_display_off(c);
+	if (status)
+		ssam_err(c, "pm: display-off notification failed: %d\n", status);
+
+	return status;
+}
+
+static void ssam_serial_hub_pm_complete(struct device *dev)
+{
+	struct ssam_controller *c = dev_get_drvdata(dev);
+	int status;
+
+	/*
+	 * Try to signal display-on. This will restore events.
+	 *
+	 * Note: Signaling display-off/display-on should normally be done from
+	 * some sort of display state notifier. As that is not available,
+	 * signal it here.
+	 */
+
+	status = ssam_ctrl_notif_display_on(c);
+	if (status)
+		ssam_err(c, "pm: display-on notification failed: %d\n", status);
+}
+
+static int ssam_serial_hub_pm_suspend(struct device *dev)
+{
+	struct ssam_controller *c = dev_get_drvdata(dev);
+	int status;
+
+	/*
+	 * Try to signal D0-exit, enable IRQ wakeup if specified. Abort on
+	 * error.
+	 */
+
+	status = ssam_ctrl_notif_d0_exit(c);
+	if (status) {
+		ssam_err(c, "pm: D0-exit notification failed: %d\n", status);
+		goto err_notif;
+	}
+
+	status = ssam_irq_arm_for_wakeup(c);
+	if (status)
+		goto err_irq;
+
+	WARN_ON(ssam_controller_suspend(c));
+	return 0;
+
+err_irq:
+	ssam_ctrl_notif_d0_entry(c);
+err_notif:
+	ssam_ctrl_notif_display_on(c);
+	return status;
+}
+
+static int ssam_serial_hub_pm_resume(struct device *dev)
+{
+	struct ssam_controller *c = dev_get_drvdata(dev);
+	int status;
+
+	WARN_ON(ssam_controller_resume(c));
+
+	/*
+	 * Try to disable IRQ wakeup (if specified) and signal D0-entry. In
+	 * case of errors, log them and try to restore normal operation state
+	 * as far as possible.
+	 *
+	 * Note: Signaling display-off/display-on should normally be done from
+	 * some sort of display state notifier. As that is not available,
+	 * signal it here.
+	 */
+
+	ssam_irq_disarm_wakeup(c);
+
+	status = ssam_ctrl_notif_d0_entry(c);
+	if (status)
+		ssam_err(c, "pm: D0-entry notification failed: %d\n", status);
+
+	return 0;
+}
+
+static int ssam_serial_hub_pm_freeze(struct device *dev)
+{
+	struct ssam_controller *c = dev_get_drvdata(dev);
+	int status;
+
+	/*
+	 * During hibernation image creation, we only have to ensure that the
+	 * EC doesn't send us any events. This is done via the display-off
+	 * and D0-exit notifications. Note that this sets up the wakeup IRQ
+	 * on the EC side, however, we have disabled it by default on our side
+	 * and won't enable it here.
+	 *
+	 * See ssam_serial_hub_poweroff() for more details on the hibernation
+	 * process.
+	 */
+
+	status = ssam_ctrl_notif_d0_exit(c);
+	if (status) {
+		ssam_err(c, "pm: D0-exit notification failed: %d\n", status);
+		ssam_ctrl_notif_display_on(c);
+		return status;
+	}
+
+	WARN_ON(ssam_controller_suspend(c));
+	return 0;
+}
+
+static int ssam_serial_hub_pm_thaw(struct device *dev)
+{
+	struct ssam_controller *c = dev_get_drvdata(dev);
+	int status;
+
+	WARN_ON(ssam_controller_resume(c));
+
+	status = ssam_ctrl_notif_d0_entry(c);
+	if (status)
+		ssam_err(c, "pm: D0-exit notification failed: %d\n", status);
+
+	return status;
+}
+
+static int ssam_serial_hub_pm_poweroff(struct device *dev)
+{
+	struct ssam_controller *c = dev_get_drvdata(dev);
+	int status;
+
+	/*
+	 * When entering hibernation and powering off the system, the EC, at
+	 * least on some models, may disable events. Without us taking care of
+	 * that, this leads to events not being enabled/restored when the
+	 * system resumes from hibernation, resulting SAM-HID subsystem devices
+	 * (i.e. keyboard, touchpad) not working, AC-plug/AC-unplug events being
+	 * gone, etc.
+	 *
+	 * To avoid these issues, we disable all registered events here (this is
+	 * likely not actually required) and restore them during the drivers PM
+	 * restore callback.
+	 *
+	 * Wakeup from the EC interrupt is not supported during hibernation,
+	 * so don't arm the IRQ here.
+	 */
+
+	status = ssam_notifier_disable_registered(c);
+	if (status) {
+		ssam_err(c, "pm: failed to disable notifiers for hibernation: %d\n",
+			 status);
+		return status;
+	}
+
+	status = ssam_ctrl_notif_d0_exit(c);
+	if (status) {
+		ssam_err(c, "pm: D0-exit notification failed: %d\n", status);
+		ssam_notifier_restore_registered(c);
+		return status;
+	}
+
+	WARN_ON(ssam_controller_suspend(c));
+	return 0;
+}
+
+static int ssam_serial_hub_pm_restore(struct device *dev)
+{
+	struct ssam_controller *c = dev_get_drvdata(dev);
+	int status;
+
+	/*
+	 * Ignore but log errors, try to restore state as much as possible in
+	 * case of failures. See ssam_serial_hub_poweroff() for more details on
+	 * the hibernation process.
+	 */
+
+	WARN_ON(ssam_controller_resume(c));
+
+	status = ssam_ctrl_notif_d0_entry(c);
+	if (status)
+		ssam_err(c, "pm: D0-entry notification failed: %d\n", status);
+
+	ssam_notifier_restore_registered(c);
+	return 0;
+}
+
+static const struct dev_pm_ops ssam_serial_hub_pm_ops = {
+	.prepare  = ssam_serial_hub_pm_prepare,
+	.complete = ssam_serial_hub_pm_complete,
+	.suspend  = ssam_serial_hub_pm_suspend,
+	.resume   = ssam_serial_hub_pm_resume,
+	.freeze   = ssam_serial_hub_pm_freeze,
+	.thaw     = ssam_serial_hub_pm_thaw,
+	.poweroff = ssam_serial_hub_pm_poweroff,
+	.restore  = ssam_serial_hub_pm_restore,
+};
+
+#else /* CONFIG_PM_SLEEP */
+
+static const struct dev_pm_ops ssam_serial_hub_pm_ops = { };
+
+#endif /* CONFIG_PM_SLEEP */
+
+
+/* -- Device/driver setup. -------------------------------------------------- */
+
+static const struct acpi_gpio_params gpio_ssam_wakeup_int = { 0, 0, false };
+static const struct acpi_gpio_params gpio_ssam_wakeup     = { 1, 0, false };
+
+static const struct acpi_gpio_mapping ssam_acpi_gpios[] = {
+	{ "ssam_wakeup-int-gpio", &gpio_ssam_wakeup_int, 1 },
+	{ "ssam_wakeup-gpio",     &gpio_ssam_wakeup,     1 },
+	{ },
+};
+
+static int ssam_serial_hub_probe(struct serdev_device *serdev)
+{
+	struct acpi_device *ssh = ACPI_COMPANION(&serdev->dev);
+	struct ssam_controller *ctrl;
+	acpi_status astatus;
+	int status;
+
+	if (gpiod_count(&serdev->dev, NULL) < 0)
+		return -ENODEV;
+
+	status = devm_acpi_dev_add_driver_gpios(&serdev->dev, ssam_acpi_gpios);
+	if (status)
+		return status;
+
+	/* Allocate controller. */
+	ctrl = kzalloc(sizeof(*ctrl), GFP_KERNEL);
+	if (!ctrl)
+		return -ENOMEM;
+
+	/* Initialize controller. */
+	status = ssam_controller_init(ctrl, serdev);
+	if (status)
+		goto err_ctrl_init;
+
+	ssam_controller_lock(ctrl);
+
+	/* Set up serdev device. */
+	serdev_device_set_drvdata(serdev, ctrl);
+	serdev_device_set_client_ops(serdev, &ssam_serdev_ops);
+	status = serdev_device_open(serdev);
+	if (status)
+		goto err_devopen;
+
+	astatus = ssam_serdev_setup_via_acpi(ssh->handle, serdev);
+	if (ACPI_FAILURE(astatus)) {
+		status = -ENXIO;
+		goto err_devinit;
+	}
+
+	/* Start controller. */
+	status = ssam_controller_start(ctrl);
+	if (status)
+		goto err_devinit;
+
+	ssam_controller_unlock(ctrl);
+
+	/*
+	 * Initial SAM requests: Log version and notify default/init power
+	 * states.
+	 */
+	status = ssam_log_firmware_version(ctrl);
+	if (status)
+		goto err_initrq;
+
+	status = ssam_ctrl_notif_d0_entry(ctrl);
+	if (status)
+		goto err_initrq;
+
+	status = ssam_ctrl_notif_display_on(ctrl);
+	if (status)
+		goto err_initrq;
+
+	status = sysfs_create_group(&serdev->dev.kobj, &ssam_sam_group);
+	if (status)
+		goto err_initrq;
+
+	/* Set up IRQ. */
+	status = ssam_irq_setup(ctrl);
+	if (status)
+		goto err_irq;
+
+	/* Finally, set main controller reference. */
+	status = ssam_try_set_controller(ctrl);
+	if (WARN_ON(status))	/* Currently, we're the only provider. */
+		goto err_mainref;
+
+	/*
+	 * TODO: The EC can wake up the system via the associated GPIO interrupt
+	 *       in multiple situations. One of which is the remaining battery
+	 *       capacity falling below a certain threshold. Normally, we should
+	 *       use the device_init_wakeup function, however, the EC also seems
+	 *       to have other reasons for waking up the system and it seems
+	 *       that Windows has additional checks whether the system should be
+	 *       resumed. In short, this causes some spurious unwanted wake-ups.
+	 *       For now let's thus default power/wakeup to false.
+	 */
+	device_set_wakeup_capable(&serdev->dev, true);
+	acpi_dev_clear_dependencies(ssh);
+
+	return 0;
+
+err_mainref:
+	ssam_irq_free(ctrl);
+err_irq:
+	sysfs_remove_group(&serdev->dev.kobj, &ssam_sam_group);
+err_initrq:
+	ssam_controller_lock(ctrl);
+	ssam_controller_shutdown(ctrl);
+err_devinit:
+	serdev_device_close(serdev);
+err_devopen:
+	ssam_controller_destroy(ctrl);
+	ssam_controller_unlock(ctrl);
+err_ctrl_init:
+	kfree(ctrl);
+	return status;
+}
+
+static void ssam_serial_hub_remove(struct serdev_device *serdev)
+{
+	struct ssam_controller *ctrl = serdev_device_get_drvdata(serdev);
+	int status;
+
+	/* Clear static reference so that no one else can get a new one. */
+	ssam_clear_controller();
+
+	/* Disable and free IRQ. */
+	ssam_irq_free(ctrl);
+
+	sysfs_remove_group(&serdev->dev.kobj, &ssam_sam_group);
+	ssam_controller_lock(ctrl);
+
+	/* Remove all client devices. */
+	ssam_remove_clients(&serdev->dev);
+
+	/* Act as if suspending to silence events. */
+	status = ssam_ctrl_notif_display_off(ctrl);
+	if (status) {
+		dev_err(&serdev->dev, "display-off notification failed: %d\n",
+			status);
+	}
+
+	status = ssam_ctrl_notif_d0_exit(ctrl);
+	if (status) {
+		dev_err(&serdev->dev, "D0-exit notification failed: %d\n",
+			status);
+	}
+
+	/* Shut down controller and remove serdev device reference from it. */
+	ssam_controller_shutdown(ctrl);
+
+	/* Shut down actual transport. */
+	serdev_device_wait_until_sent(serdev, 0);
+	serdev_device_close(serdev);
+
+	/* Drop our controller reference. */
+	ssam_controller_unlock(ctrl);
+	ssam_controller_put(ctrl);
+
+	device_set_wakeup_capable(&serdev->dev, false);
+}
+
+static const struct acpi_device_id ssam_serial_hub_match[] = {
+	{ "MSHW0084", 0 },
+	{ },
+};
+MODULE_DEVICE_TABLE(acpi, ssam_serial_hub_match);
+
+static struct serdev_device_driver ssam_serial_hub = {
+	.probe = ssam_serial_hub_probe,
+	.remove = ssam_serial_hub_remove,
+	.driver = {
+		.name = "surface_serial_hub",
+		.acpi_match_table = ssam_serial_hub_match,
+		.pm = &ssam_serial_hub_pm_ops,
+		.shutdown = ssam_serial_hub_shutdown,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+
+
+/* -- Module setup. --------------------------------------------------------- */
+
+static int __init ssam_core_init(void)
+{
+	int status;
+
+	status = ssam_bus_register();
+	if (status)
+		goto err_bus;
+
+	status = ssh_ctrl_packet_cache_init();
+	if (status)
+		goto err_cpkg;
+
+	status = ssam_event_item_cache_init();
+	if (status)
+		goto err_evitem;
+
+	status = serdev_device_driver_register(&ssam_serial_hub);
+	if (status)
+		goto err_register;
+
+	return 0;
+
+err_register:
+	ssam_event_item_cache_destroy();
+err_evitem:
+	ssh_ctrl_packet_cache_destroy();
+err_cpkg:
+	ssam_bus_unregister();
+err_bus:
+	return status;
+}
+subsys_initcall(ssam_core_init);
+
+static void __exit ssam_core_exit(void)
+{
+	serdev_device_driver_unregister(&ssam_serial_hub);
+	ssam_event_item_cache_destroy();
+	ssh_ctrl_packet_cache_destroy();
+	ssam_bus_unregister();
+}
+module_exit(ssam_core_exit);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("Subsystem and Surface Serial Hub driver for Surface System Aggregator Module");
+MODULE_LICENSE("GPL");
diff --git a/drivers/platform/surface/aggregator/ssh_msgb.h b/drivers/platform/surface/aggregator/ssh_msgb.h
new file mode 100644
index 000000000..f3ecad92e
--- /dev/null
+++ b/drivers/platform/surface/aggregator/ssh_msgb.h
@@ -0,0 +1,205 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * SSH message builder functions.
+ *
+ * Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#ifndef _SURFACE_AGGREGATOR_SSH_MSGB_H
+#define _SURFACE_AGGREGATOR_SSH_MSGB_H
+
+#include <asm/unaligned.h>
+#include <linux/types.h>
+
+#include <linux/surface_aggregator/controller.h>
+#include <linux/surface_aggregator/serial_hub.h>
+
+/**
+ * struct msgbuf - Buffer struct to construct SSH messages.
+ * @begin: Pointer to the beginning of the allocated buffer space.
+ * @end:   Pointer to the end (one past last element) of the allocated buffer
+ *         space.
+ * @ptr:   Pointer to the first free element in the buffer.
+ */
+struct msgbuf {
+	u8 *begin;
+	u8 *end;
+	u8 *ptr;
+};
+
+/**
+ * msgb_init() - Initialize the given message buffer struct.
+ * @msgb: The buffer struct to initialize
+ * @ptr:  Pointer to the underlying memory by which the buffer will be backed.
+ * @cap:  Size of the underlying memory.
+ *
+ * Initialize the given message buffer struct using the provided memory as
+ * backing.
+ */
+static inline void msgb_init(struct msgbuf *msgb, u8 *ptr, size_t cap)
+{
+	msgb->begin = ptr;
+	msgb->end = ptr + cap;
+	msgb->ptr = ptr;
+}
+
+/**
+ * msgb_bytes_used() - Return the current number of bytes used in the buffer.
+ * @msgb: The message buffer.
+ */
+static inline size_t msgb_bytes_used(const struct msgbuf *msgb)
+{
+	return msgb->ptr - msgb->begin;
+}
+
+static inline void __msgb_push_u8(struct msgbuf *msgb, u8 value)
+{
+	*msgb->ptr = value;
+	msgb->ptr += sizeof(u8);
+}
+
+static inline void __msgb_push_u16(struct msgbuf *msgb, u16 value)
+{
+	put_unaligned_le16(value, msgb->ptr);
+	msgb->ptr += sizeof(u16);
+}
+
+/**
+ * msgb_push_u16() - Push a u16 value to the buffer.
+ * @msgb:  The message buffer.
+ * @value: The value to push to the buffer.
+ */
+static inline void msgb_push_u16(struct msgbuf *msgb, u16 value)
+{
+	if (WARN_ON(msgb->ptr + sizeof(u16) > msgb->end))
+		return;
+
+	__msgb_push_u16(msgb, value);
+}
+
+/**
+ * msgb_push_syn() - Push SSH SYN bytes to the buffer.
+ * @msgb: The message buffer.
+ */
+static inline void msgb_push_syn(struct msgbuf *msgb)
+{
+	msgb_push_u16(msgb, SSH_MSG_SYN);
+}
+
+/**
+ * msgb_push_buf() - Push raw data to the buffer.
+ * @msgb: The message buffer.
+ * @buf:  The data to push to the buffer.
+ * @len:  The length of the data to push to the buffer.
+ */
+static inline void msgb_push_buf(struct msgbuf *msgb, const u8 *buf, size_t len)
+{
+	msgb->ptr = memcpy(msgb->ptr, buf, len) + len;
+}
+
+/**
+ * msgb_push_crc() - Compute CRC and push it to the buffer.
+ * @msgb: The message buffer.
+ * @buf:  The data for which the CRC should be computed.
+ * @len:  The length of the data for which the CRC should be computed.
+ */
+static inline void msgb_push_crc(struct msgbuf *msgb, const u8 *buf, size_t len)
+{
+	msgb_push_u16(msgb, ssh_crc(buf, len));
+}
+
+/**
+ * msgb_push_frame() - Push a SSH message frame header to the buffer.
+ * @msgb: The message buffer
+ * @ty:   The type of the frame.
+ * @len:  The length of the payload of the frame.
+ * @seq:  The sequence ID of the frame/packet.
+ */
+static inline void msgb_push_frame(struct msgbuf *msgb, u8 ty, u16 len, u8 seq)
+{
+	u8 *const begin = msgb->ptr;
+
+	if (WARN_ON(msgb->ptr + sizeof(struct ssh_frame) > msgb->end))
+		return;
+
+	__msgb_push_u8(msgb, ty);	/* Frame type. */
+	__msgb_push_u16(msgb, len);	/* Frame payload length. */
+	__msgb_push_u8(msgb, seq);	/* Frame sequence ID. */
+
+	msgb_push_crc(msgb, begin, msgb->ptr - begin);
+}
+
+/**
+ * msgb_push_ack() - Push a SSH ACK frame to the buffer.
+ * @msgb: The message buffer
+ * @seq:  The sequence ID of the frame/packet to be ACKed.
+ */
+static inline void msgb_push_ack(struct msgbuf *msgb, u8 seq)
+{
+	/* SYN. */
+	msgb_push_syn(msgb);
+
+	/* ACK-type frame + CRC. */
+	msgb_push_frame(msgb, SSH_FRAME_TYPE_ACK, 0x00, seq);
+
+	/* Payload CRC (ACK-type frames do not have a payload). */
+	msgb_push_crc(msgb, msgb->ptr, 0);
+}
+
+/**
+ * msgb_push_nak() - Push a SSH NAK frame to the buffer.
+ * @msgb: The message buffer
+ */
+static inline void msgb_push_nak(struct msgbuf *msgb)
+{
+	/* SYN. */
+	msgb_push_syn(msgb);
+
+	/* NAK-type frame + CRC. */
+	msgb_push_frame(msgb, SSH_FRAME_TYPE_NAK, 0x00, 0x00);
+
+	/* Payload CRC (ACK-type frames do not have a payload). */
+	msgb_push_crc(msgb, msgb->ptr, 0);
+}
+
+/**
+ * msgb_push_cmd() - Push a SSH command frame with payload to the buffer.
+ * @msgb: The message buffer.
+ * @seq:  The sequence ID (SEQ) of the frame/packet.
+ * @rqid: The request ID (RQID) of the request contained in the frame.
+ * @rqst: The request to wrap in the frame.
+ */
+static inline void msgb_push_cmd(struct msgbuf *msgb, u8 seq, u16 rqid,
+				 const struct ssam_request *rqst)
+{
+	const u8 type = SSH_FRAME_TYPE_DATA_SEQ;
+	u8 *cmd;
+
+	/* SYN. */
+	msgb_push_syn(msgb);
+
+	/* Command frame + CRC. */
+	msgb_push_frame(msgb, type, sizeof(struct ssh_command) + rqst->length, seq);
+
+	/* Frame payload: Command struct + payload. */
+	if (WARN_ON(msgb->ptr + sizeof(struct ssh_command) > msgb->end))
+		return;
+
+	cmd = msgb->ptr;
+
+	__msgb_push_u8(msgb, SSH_PLD_TYPE_CMD);		/* Payload type. */
+	__msgb_push_u8(msgb, rqst->target_category);	/* Target category. */
+	__msgb_push_u8(msgb, rqst->target_id);		/* Target ID (out). */
+	__msgb_push_u8(msgb, 0x00);			/* Target ID (in). */
+	__msgb_push_u8(msgb, rqst->instance_id);	/* Instance ID. */
+	__msgb_push_u16(msgb, rqid);			/* Request ID. */
+	__msgb_push_u8(msgb, rqst->command_id);		/* Command ID. */
+
+	/* Command payload. */
+	msgb_push_buf(msgb, rqst->payload, rqst->length);
+
+	/* CRC for command struct + payload. */
+	msgb_push_crc(msgb, cmd, msgb->ptr - cmd);
+}
+
+#endif /* _SURFACE_AGGREGATOR_SSH_MSGB_H */
diff --git a/drivers/platform/surface/aggregator/ssh_packet_layer.c b/drivers/platform/surface/aggregator/ssh_packet_layer.c
new file mode 100644
index 000000000..def8d7ac5
--- /dev/null
+++ b/drivers/platform/surface/aggregator/ssh_packet_layer.c
@@ -0,0 +1,2086 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * SSH packet transport layer.
+ *
+ * Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#include <asm/unaligned.h>
+#include <linux/atomic.h>
+#include <linux/error-injection.h>
+#include <linux/jiffies.h>
+#include <linux/kfifo.h>
+#include <linux/kref.h>
+#include <linux/kthread.h>
+#include <linux/ktime.h>
+#include <linux/limits.h>
+#include <linux/list.h>
+#include <linux/lockdep.h>
+#include <linux/serdev.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/workqueue.h>
+
+#include <linux/surface_aggregator/serial_hub.h>
+
+#include "ssh_msgb.h"
+#include "ssh_packet_layer.h"
+#include "ssh_parser.h"
+
+#include "trace.h"
+
+/*
+ * To simplify reasoning about the code below, we define a few concepts. The
+ * system below is similar to a state-machine for packets, however, there are
+ * too many states to explicitly write them down. To (somewhat) manage the
+ * states and packets we rely on flags, reference counting, and some simple
+ * concepts. State transitions are triggered by actions.
+ *
+ * >> Actions <<
+ *
+ * - submit
+ * - transmission start (process next item in queue)
+ * - transmission finished (guaranteed to never be parallel to transmission
+ *   start)
+ * - ACK received
+ * - NAK received (this is equivalent to issuing re-submit for all pending
+ *   packets)
+ * - timeout (this is equivalent to re-issuing a submit or canceling)
+ * - cancel (non-pending and pending)
+ *
+ * >> Data Structures, Packet Ownership, General Overview <<
+ *
+ * The code below employs two main data structures: The packet queue,
+ * containing all packets scheduled for transmission, and the set of pending
+ * packets, containing all packets awaiting an ACK.
+ *
+ * Shared ownership of a packet is controlled via reference counting. Inside
+ * the transport system are a total of five packet owners:
+ *
+ * - the packet queue,
+ * - the pending set,
+ * - the transmitter thread,
+ * - the receiver thread (via ACKing), and
+ * - the timeout work item.
+ *
+ * Normal operation is as follows: The initial reference of the packet is
+ * obtained by submitting the packet and queuing it. The receiver thread takes
+ * packets from the queue. By doing this, it does not increment the refcount
+ * but takes over the reference (removing it from the queue). If the packet is
+ * sequenced (i.e. needs to be ACKed by the client), the transmitter thread
+ * sets-up the timeout and adds the packet to the pending set before starting
+ * to transmit it. As the timeout is handled by a reaper task, no additional
+ * reference for it is needed. After the transmit is done, the reference held
+ * by the transmitter thread is dropped. If the packet is unsequenced (i.e.
+ * does not need an ACK), the packet is completed by the transmitter thread
+ * before dropping that reference.
+ *
+ * On receival of an ACK, the receiver thread removes and obtains the
+ * reference to the packet from the pending set. The receiver thread will then
+ * complete the packet and drop its reference.
+ *
+ * On receival of a NAK, the receiver thread re-submits all currently pending
+ * packets.
+ *
+ * Packet timeouts are detected by the timeout reaper. This is a task,
+ * scheduled depending on the earliest packet timeout expiration date,
+ * checking all currently pending packets if their timeout has expired. If the
+ * timeout of a packet has expired, it is re-submitted and the number of tries
+ * of this packet is incremented. If this number reaches its limit, the packet
+ * will be completed with a failure.
+ *
+ * On transmission failure (such as repeated packet timeouts), the completion
+ * callback is immediately run by on thread on which the error was detected.
+ *
+ * To ensure that a packet eventually leaves the system it is marked as
+ * "locked" directly before it is going to be completed or when it is
+ * canceled. Marking a packet as "locked" has the effect that passing and
+ * creating new references of the packet is disallowed. This means that the
+ * packet cannot be added to the queue, the pending set, and the timeout, or
+ * be picked up by the transmitter thread or receiver thread. To remove a
+ * packet from the system it has to be marked as locked and subsequently all
+ * references from the data structures (queue, pending) have to be removed.
+ * References held by threads will eventually be dropped automatically as
+ * their execution progresses.
+ *
+ * Note that the packet completion callback is, in case of success and for a
+ * sequenced packet, guaranteed to run on the receiver thread, thus providing
+ * a way to reliably identify responses to the packet. The packet completion
+ * callback is only run once and it does not indicate that the packet has
+ * fully left the system (for this, one should rely on the release method,
+ * triggered when the reference count of the packet reaches zero). In case of
+ * re-submission (and with somewhat unlikely timing), it may be possible that
+ * the packet is being re-transmitted while the completion callback runs.
+ * Completion will occur both on success and internal error, as well as when
+ * the packet is canceled.
+ *
+ * >> Flags <<
+ *
+ * Flags are used to indicate the state and progression of a packet. Some flags
+ * have stricter guarantees than other:
+ *
+ * - locked
+ *   Indicates if the packet is locked. If the packet is locked, passing and/or
+ *   creating additional references to the packet is forbidden. The packet thus
+ *   may not be queued, dequeued, or removed or added to the pending set. Note
+ *   that the packet state flags may still change (e.g. it may be marked as
+ *   ACKed, transmitted, ...).
+ *
+ * - completed
+ *   Indicates if the packet completion callback has been executed or is about
+ *   to be executed. This flag is used to ensure that the packet completion
+ *   callback is only run once.
+ *
+ * - queued
+ *   Indicates if a packet is present in the submission queue or not. This flag
+ *   must only be modified with the queue lock held, and must be coherent to the
+ *   presence of the packet in the queue.
+ *
+ * - pending
+ *   Indicates if a packet is present in the set of pending packets or not.
+ *   This flag must only be modified with the pending lock held, and must be
+ *   coherent to the presence of the packet in the pending set.
+ *
+ * - transmitting
+ *   Indicates if the packet is currently transmitting. In case of
+ *   re-transmissions, it is only safe to wait on the "transmitted" completion
+ *   after this flag has been set. The completion will be set both in success
+ *   and error case.
+ *
+ * - transmitted
+ *   Indicates if the packet has been transmitted. This flag is not cleared by
+ *   the system, thus it indicates the first transmission only.
+ *
+ * - acked
+ *   Indicates if the packet has been acknowledged by the client. There are no
+ *   other guarantees given. For example, the packet may still be canceled
+ *   and/or the completion may be triggered an error even though this bit is
+ *   set. Rely on the status provided to the completion callback instead.
+ *
+ * - canceled
+ *   Indicates if the packet has been canceled from the outside. There are no
+ *   other guarantees given. Specifically, the packet may be completed by
+ *   another part of the system before the cancellation attempts to complete it.
+ *
+ * >> General Notes <<
+ *
+ * - To avoid deadlocks, if both queue and pending locks are required, the
+ *   pending lock must be acquired before the queue lock.
+ *
+ * - The packet priority must be accessed only while holding the queue lock.
+ *
+ * - The packet timestamp must be accessed only while holding the pending
+ *   lock.
+ */
+
+/*
+ * SSH_PTL_MAX_PACKET_TRIES - Maximum transmission attempts for packet.
+ *
+ * Maximum number of transmission attempts per sequenced packet in case of
+ * time-outs. Must be smaller than 16. If the packet times out after this
+ * amount of tries, the packet will be completed with %-ETIMEDOUT as status
+ * code.
+ */
+#define SSH_PTL_MAX_PACKET_TRIES		3
+
+/*
+ * SSH_PTL_TX_TIMEOUT - Packet transmission timeout.
+ *
+ * Timeout in jiffies for packet transmission via the underlying serial
+ * device. If transmitting the packet takes longer than this timeout, the
+ * packet will be completed with -ETIMEDOUT. It will not be re-submitted.
+ */
+#define SSH_PTL_TX_TIMEOUT			HZ
+
+/*
+ * SSH_PTL_PACKET_TIMEOUT - Packet response timeout.
+ *
+ * Timeout as ktime_t delta for ACKs. If we have not received an ACK in this
+ * time-frame after starting transmission, the packet will be re-submitted.
+ */
+#define SSH_PTL_PACKET_TIMEOUT			ms_to_ktime(1000)
+
+/*
+ * SSH_PTL_PACKET_TIMEOUT_RESOLUTION - Packet timeout granularity.
+ *
+ * Time-resolution for timeouts. Should be larger than one jiffy to avoid
+ * direct re-scheduling of reaper work_struct.
+ */
+#define SSH_PTL_PACKET_TIMEOUT_RESOLUTION	ms_to_ktime(max(2000 / HZ, 50))
+
+/*
+ * SSH_PTL_MAX_PENDING - Maximum number of pending packets.
+ *
+ * Maximum number of sequenced packets concurrently waiting for an ACK.
+ * Packets marked as blocking will not be transmitted while this limit is
+ * reached.
+ */
+#define SSH_PTL_MAX_PENDING			1
+
+/*
+ * SSH_PTL_RX_BUF_LEN - Evaluation-buffer size in bytes.
+ */
+#define SSH_PTL_RX_BUF_LEN			4096
+
+/*
+ * SSH_PTL_RX_FIFO_LEN - Fifo input-buffer size in bytes.
+ */
+#define SSH_PTL_RX_FIFO_LEN			4096
+
+#ifdef CONFIG_SURFACE_AGGREGATOR_ERROR_INJECTION
+
+/**
+ * ssh_ptl_should_drop_ack_packet() - Error injection hook to drop ACK packets.
+ *
+ * Useful to test detection and handling of automated re-transmits by the EC.
+ * Specifically of packets that the EC considers not-ACKed but the driver
+ * already considers ACKed (due to dropped ACK). In this case, the EC
+ * re-transmits the packet-to-be-ACKed and the driver should detect it as
+ * duplicate/already handled. Note that the driver should still send an ACK
+ * for the re-transmitted packet.
+ */
+static noinline bool ssh_ptl_should_drop_ack_packet(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_drop_ack_packet, TRUE);
+
+/**
+ * ssh_ptl_should_drop_nak_packet() - Error injection hook to drop NAK packets.
+ *
+ * Useful to test/force automated (timeout-based) re-transmit by the EC.
+ * Specifically, packets that have not reached the driver completely/with valid
+ * checksums. Only useful in combination with receival of (injected) bad data.
+ */
+static noinline bool ssh_ptl_should_drop_nak_packet(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_drop_nak_packet, TRUE);
+
+/**
+ * ssh_ptl_should_drop_dsq_packet() - Error injection hook to drop sequenced
+ * data packet.
+ *
+ * Useful to test re-transmit timeout of the driver. If the data packet has not
+ * been ACKed after a certain time, the driver should re-transmit the packet up
+ * to limited number of times defined in SSH_PTL_MAX_PACKET_TRIES.
+ */
+static noinline bool ssh_ptl_should_drop_dsq_packet(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_drop_dsq_packet, TRUE);
+
+/**
+ * ssh_ptl_should_fail_write() - Error injection hook to make
+ * serdev_device_write() fail.
+ *
+ * Hook to simulate errors in serdev_device_write when transmitting packets.
+ */
+static noinline int ssh_ptl_should_fail_write(void)
+{
+	return 0;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_fail_write, ERRNO);
+
+/**
+ * ssh_ptl_should_corrupt_tx_data() - Error injection hook to simulate invalid
+ * data being sent to the EC.
+ *
+ * Hook to simulate corrupt/invalid data being sent from host (driver) to EC.
+ * Causes the packet data to be actively corrupted by overwriting it with
+ * pre-defined values, such that it becomes invalid, causing the EC to respond
+ * with a NAK packet. Useful to test handling of NAK packets received by the
+ * driver.
+ */
+static noinline bool ssh_ptl_should_corrupt_tx_data(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_corrupt_tx_data, TRUE);
+
+/**
+ * ssh_ptl_should_corrupt_rx_syn() - Error injection hook to simulate invalid
+ * data being sent by the EC.
+ *
+ * Hook to simulate invalid SYN bytes, i.e. an invalid start of messages and
+ * test handling thereof in the driver.
+ */
+static noinline bool ssh_ptl_should_corrupt_rx_syn(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_corrupt_rx_syn, TRUE);
+
+/**
+ * ssh_ptl_should_corrupt_rx_data() - Error injection hook to simulate invalid
+ * data being sent by the EC.
+ *
+ * Hook to simulate invalid data/checksum of the message frame and test handling
+ * thereof in the driver.
+ */
+static noinline bool ssh_ptl_should_corrupt_rx_data(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_ptl_should_corrupt_rx_data, TRUE);
+
+static bool __ssh_ptl_should_drop_ack_packet(struct ssh_packet *packet)
+{
+	if (likely(!ssh_ptl_should_drop_ack_packet()))
+		return false;
+
+	trace_ssam_ei_tx_drop_ack_packet(packet);
+	ptl_info(packet->ptl, "packet error injection: dropping ACK packet %p\n",
+		 packet);
+
+	return true;
+}
+
+static bool __ssh_ptl_should_drop_nak_packet(struct ssh_packet *packet)
+{
+	if (likely(!ssh_ptl_should_drop_nak_packet()))
+		return false;
+
+	trace_ssam_ei_tx_drop_nak_packet(packet);
+	ptl_info(packet->ptl, "packet error injection: dropping NAK packet %p\n",
+		 packet);
+
+	return true;
+}
+
+static bool __ssh_ptl_should_drop_dsq_packet(struct ssh_packet *packet)
+{
+	if (likely(!ssh_ptl_should_drop_dsq_packet()))
+		return false;
+
+	trace_ssam_ei_tx_drop_dsq_packet(packet);
+	ptl_info(packet->ptl,
+		 "packet error injection: dropping sequenced data packet %p\n",
+		 packet);
+
+	return true;
+}
+
+static bool ssh_ptl_should_drop_packet(struct ssh_packet *packet)
+{
+	/* Ignore packets that don't carry any data (i.e. flush). */
+	if (!packet->data.ptr || !packet->data.len)
+		return false;
+
+	switch (packet->data.ptr[SSH_MSGOFFSET_FRAME(type)]) {
+	case SSH_FRAME_TYPE_ACK:
+		return __ssh_ptl_should_drop_ack_packet(packet);
+
+	case SSH_FRAME_TYPE_NAK:
+		return __ssh_ptl_should_drop_nak_packet(packet);
+
+	case SSH_FRAME_TYPE_DATA_SEQ:
+		return __ssh_ptl_should_drop_dsq_packet(packet);
+
+	default:
+		return false;
+	}
+}
+
+static int ssh_ptl_write_buf(struct ssh_ptl *ptl, struct ssh_packet *packet,
+			     const unsigned char *buf, size_t count)
+{
+	int status;
+
+	status = ssh_ptl_should_fail_write();
+	if (unlikely(status)) {
+		trace_ssam_ei_tx_fail_write(packet, status);
+		ptl_info(packet->ptl,
+			 "packet error injection: simulating transmit error %d, packet %p\n",
+			 status, packet);
+
+		return status;
+	}
+
+	return serdev_device_write_buf(ptl->serdev, buf, count);
+}
+
+static void ssh_ptl_tx_inject_invalid_data(struct ssh_packet *packet)
+{
+	/* Ignore packets that don't carry any data (i.e. flush). */
+	if (!packet->data.ptr || !packet->data.len)
+		return;
+
+	/* Only allow sequenced data packets to be modified. */
+	if (packet->data.ptr[SSH_MSGOFFSET_FRAME(type)] != SSH_FRAME_TYPE_DATA_SEQ)
+		return;
+
+	if (likely(!ssh_ptl_should_corrupt_tx_data()))
+		return;
+
+	trace_ssam_ei_tx_corrupt_data(packet);
+	ptl_info(packet->ptl,
+		 "packet error injection: simulating invalid transmit data on packet %p\n",
+		 packet);
+
+	/*
+	 * NB: The value 0xb3 has been chosen more or less randomly so that it
+	 * doesn't have any (major) overlap with the SYN bytes (aa 55) and is
+	 * non-trivial (i.e. non-zero, non-0xff).
+	 */
+	memset(packet->data.ptr, 0xb3, packet->data.len);
+}
+
+static void ssh_ptl_rx_inject_invalid_syn(struct ssh_ptl *ptl,
+					  struct ssam_span *data)
+{
+	struct ssam_span frame;
+
+	/* Check if there actually is something to corrupt. */
+	if (!sshp_find_syn(data, &frame))
+		return;
+
+	if (likely(!ssh_ptl_should_corrupt_rx_syn()))
+		return;
+
+	trace_ssam_ei_rx_corrupt_syn(data->len);
+
+	data->ptr[1] = 0xb3;	/* Set second byte of SYN to "random" value. */
+}
+
+static void ssh_ptl_rx_inject_invalid_data(struct ssh_ptl *ptl,
+					   struct ssam_span *frame)
+{
+	size_t payload_len, message_len;
+	struct ssh_frame *sshf;
+
+	/* Ignore incomplete messages, will get handled once it's complete. */
+	if (frame->len < SSH_MESSAGE_LENGTH(0))
+		return;
+
+	/* Ignore incomplete messages, part 2. */
+	payload_len = get_unaligned_le16(&frame->ptr[SSH_MSGOFFSET_FRAME(len)]);
+	message_len = SSH_MESSAGE_LENGTH(payload_len);
+	if (frame->len < message_len)
+		return;
+
+	if (likely(!ssh_ptl_should_corrupt_rx_data()))
+		return;
+
+	sshf = (struct ssh_frame *)&frame->ptr[SSH_MSGOFFSET_FRAME(type)];
+	trace_ssam_ei_rx_corrupt_data(sshf);
+
+	/*
+	 * Flip bits in first byte of payload checksum. This is basically
+	 * equivalent to a payload/frame data error without us having to worry
+	 * about (the, arguably pretty small, probability of) accidental
+	 * checksum collisions.
+	 */
+	frame->ptr[frame->len - 2] = ~frame->ptr[frame->len - 2];
+}
+
+#else /* CONFIG_SURFACE_AGGREGATOR_ERROR_INJECTION */
+
+static inline bool ssh_ptl_should_drop_packet(struct ssh_packet *packet)
+{
+	return false;
+}
+
+static inline int ssh_ptl_write_buf(struct ssh_ptl *ptl,
+				    struct ssh_packet *packet,
+				    const unsigned char *buf,
+				    size_t count)
+{
+	return serdev_device_write_buf(ptl->serdev, buf, count);
+}
+
+static inline void ssh_ptl_tx_inject_invalid_data(struct ssh_packet *packet)
+{
+}
+
+static inline void ssh_ptl_rx_inject_invalid_syn(struct ssh_ptl *ptl,
+						 struct ssam_span *data)
+{
+}
+
+static inline void ssh_ptl_rx_inject_invalid_data(struct ssh_ptl *ptl,
+						  struct ssam_span *frame)
+{
+}
+
+#endif /* CONFIG_SURFACE_AGGREGATOR_ERROR_INJECTION */
+
+static void __ssh_ptl_packet_release(struct kref *kref)
+{
+	struct ssh_packet *p = container_of(kref, struct ssh_packet, refcnt);
+
+	trace_ssam_packet_release(p);
+
+	ptl_dbg_cond(p->ptl, "ptl: releasing packet %p\n", p);
+	p->ops->release(p);
+}
+
+/**
+ * ssh_packet_get() - Increment reference count of packet.
+ * @packet: The packet to increment the reference count of.
+ *
+ * Increments the reference count of the given packet. See ssh_packet_put()
+ * for the counter-part of this function.
+ *
+ * Return: Returns the packet provided as input.
+ */
+struct ssh_packet *ssh_packet_get(struct ssh_packet *packet)
+{
+	if (packet)
+		kref_get(&packet->refcnt);
+	return packet;
+}
+EXPORT_SYMBOL_GPL(ssh_packet_get);
+
+/**
+ * ssh_packet_put() - Decrement reference count of packet.
+ * @packet: The packet to decrement the reference count of.
+ *
+ * If the reference count reaches zero, the ``release`` callback specified in
+ * the packet's &struct ssh_packet_ops, i.e. ``packet->ops->release``, will be
+ * called.
+ *
+ * See ssh_packet_get() for the counter-part of this function.
+ */
+void ssh_packet_put(struct ssh_packet *packet)
+{
+	if (packet)
+		kref_put(&packet->refcnt, __ssh_ptl_packet_release);
+}
+EXPORT_SYMBOL_GPL(ssh_packet_put);
+
+static u8 ssh_packet_get_seq(struct ssh_packet *packet)
+{
+	return packet->data.ptr[SSH_MSGOFFSET_FRAME(seq)];
+}
+
+/**
+ * ssh_packet_init() - Initialize SSH packet.
+ * @packet:   The packet to initialize.
+ * @type:     Type-flags of the packet.
+ * @priority: Priority of the packet. See SSH_PACKET_PRIORITY() for details.
+ * @ops:      Packet operations.
+ *
+ * Initializes the given SSH packet. Sets the transmission buffer pointer to
+ * %NULL and the transmission buffer length to zero. For data-type packets,
+ * this buffer has to be set separately via ssh_packet_set_data() before
+ * submission, and must contain a valid SSH message, i.e. frame with optional
+ * payload of any type.
+ */
+void ssh_packet_init(struct ssh_packet *packet, unsigned long type,
+		     u8 priority, const struct ssh_packet_ops *ops)
+{
+	kref_init(&packet->refcnt);
+
+	packet->ptl = NULL;
+	INIT_LIST_HEAD(&packet->queue_node);
+	INIT_LIST_HEAD(&packet->pending_node);
+
+	packet->state = type & SSH_PACKET_FLAGS_TY_MASK;
+	packet->priority = priority;
+	packet->timestamp = KTIME_MAX;
+
+	packet->data.ptr = NULL;
+	packet->data.len = 0;
+
+	packet->ops = ops;
+}
+
+static struct kmem_cache *ssh_ctrl_packet_cache;
+
+/**
+ * ssh_ctrl_packet_cache_init() - Initialize the control packet cache.
+ */
+int ssh_ctrl_packet_cache_init(void)
+{
+	const unsigned int size = sizeof(struct ssh_packet) + SSH_MSG_LEN_CTRL;
+	const unsigned int align = __alignof__(struct ssh_packet);
+	struct kmem_cache *cache;
+
+	cache = kmem_cache_create("ssam_ctrl_packet", size, align, 0, NULL);
+	if (!cache)
+		return -ENOMEM;
+
+	ssh_ctrl_packet_cache = cache;
+	return 0;
+}
+
+/**
+ * ssh_ctrl_packet_cache_destroy() - Deinitialize the control packet cache.
+ */
+void ssh_ctrl_packet_cache_destroy(void)
+{
+	kmem_cache_destroy(ssh_ctrl_packet_cache);
+	ssh_ctrl_packet_cache = NULL;
+}
+
+/**
+ * ssh_ctrl_packet_alloc() - Allocate packet from control packet cache.
+ * @packet: Where the pointer to the newly allocated packet should be stored.
+ * @buffer: The buffer corresponding to this packet.
+ * @flags:  Flags used for allocation.
+ *
+ * Allocates a packet and corresponding transport buffer from the control
+ * packet cache. Sets the packet's buffer reference to the allocated buffer.
+ * The packet must be freed via ssh_ctrl_packet_free(), which will also free
+ * the corresponding buffer. The corresponding buffer must not be freed
+ * separately. Intended to be used with %ssh_ptl_ctrl_packet_ops as packet
+ * operations.
+ *
+ * Return: Returns zero on success, %-ENOMEM if the allocation failed.
+ */
+static int ssh_ctrl_packet_alloc(struct ssh_packet **packet,
+				 struct ssam_span *buffer, gfp_t flags)
+{
+	*packet = kmem_cache_alloc(ssh_ctrl_packet_cache, flags);
+	if (!*packet)
+		return -ENOMEM;
+
+	buffer->ptr = (u8 *)(*packet + 1);
+	buffer->len = SSH_MSG_LEN_CTRL;
+
+	trace_ssam_ctrl_packet_alloc(*packet, buffer->len);
+	return 0;
+}
+
+/**
+ * ssh_ctrl_packet_free() - Free packet allocated from control packet cache.
+ * @p: The packet to free.
+ */
+static void ssh_ctrl_packet_free(struct ssh_packet *p)
+{
+	trace_ssam_ctrl_packet_free(p);
+	kmem_cache_free(ssh_ctrl_packet_cache, p);
+}
+
+static const struct ssh_packet_ops ssh_ptl_ctrl_packet_ops = {
+	.complete = NULL,
+	.release = ssh_ctrl_packet_free,
+};
+
+static void ssh_ptl_timeout_reaper_mod(struct ssh_ptl *ptl, ktime_t now,
+				       ktime_t expires)
+{
+	unsigned long delta = msecs_to_jiffies(ktime_ms_delta(expires, now));
+	ktime_t aexp = ktime_add(expires, SSH_PTL_PACKET_TIMEOUT_RESOLUTION);
+
+	spin_lock(&ptl->rtx_timeout.lock);
+
+	/* Re-adjust / schedule reaper only if it is above resolution delta. */
+	if (ktime_before(aexp, ptl->rtx_timeout.expires)) {
+		ptl->rtx_timeout.expires = expires;
+		mod_delayed_work(system_wq, &ptl->rtx_timeout.reaper, delta);
+	}
+
+	spin_unlock(&ptl->rtx_timeout.lock);
+}
+
+/* Must be called with queue lock held. */
+static void ssh_packet_next_try(struct ssh_packet *p)
+{
+	u8 base = ssh_packet_priority_get_base(p->priority);
+	u8 try = ssh_packet_priority_get_try(p->priority);
+
+	lockdep_assert_held(&p->ptl->queue.lock);
+
+	/*
+	 * Ensure that we write the priority in one go via WRITE_ONCE() so we
+	 * can access it via READ_ONCE() for tracing. Note that other access
+	 * is guarded by the queue lock, so no need to use READ_ONCE() there.
+	 */
+	WRITE_ONCE(p->priority, __SSH_PACKET_PRIORITY(base, try + 1));
+}
+
+/* Must be called with queue lock held. */
+static struct list_head *__ssh_ptl_queue_find_entrypoint(struct ssh_packet *p)
+{
+	struct list_head *head;
+	struct ssh_packet *q;
+
+	lockdep_assert_held(&p->ptl->queue.lock);
+
+	/*
+	 * We generally assume that there are less control (ACK/NAK) packets
+	 * and re-submitted data packets as there are normal data packets (at
+	 * least in situations in which many packets are queued; if there
+	 * aren't many packets queued the decision on how to iterate should be
+	 * basically irrelevant; the number of control/data packets is more or
+	 * less limited via the maximum number of pending packets). Thus, when
+	 * inserting a control or re-submitted data packet, (determined by
+	 * their priority), we search from front to back. Normal data packets
+	 * are, usually queued directly at the tail of the queue, so for those
+	 * search from back to front.
+	 */
+
+	if (p->priority > SSH_PACKET_PRIORITY(DATA, 0)) {
+		list_for_each(head, &p->ptl->queue.head) {
+			q = list_entry(head, struct ssh_packet, queue_node);
+
+			if (q->priority < p->priority)
+				break;
+		}
+	} else {
+		list_for_each_prev(head, &p->ptl->queue.head) {
+			q = list_entry(head, struct ssh_packet, queue_node);
+
+			if (q->priority >= p->priority) {
+				head = head->next;
+				break;
+			}
+		}
+	}
+
+	return head;
+}
+
+/* Must be called with queue lock held. */
+static int __ssh_ptl_queue_push(struct ssh_packet *packet)
+{
+	struct ssh_ptl *ptl = packet->ptl;
+	struct list_head *head;
+
+	lockdep_assert_held(&ptl->queue.lock);
+
+	if (test_bit(SSH_PTL_SF_SHUTDOWN_BIT, &ptl->state))
+		return -ESHUTDOWN;
+
+	/* Avoid further transitions when canceling/completing. */
+	if (test_bit(SSH_PACKET_SF_LOCKED_BIT, &packet->state))
+		return -EINVAL;
+
+	/* If this packet has already been queued, do not add it. */
+	if (test_and_set_bit(SSH_PACKET_SF_QUEUED_BIT, &packet->state))
+		return -EALREADY;
+
+	head = __ssh_ptl_queue_find_entrypoint(packet);
+
+	list_add_tail(&ssh_packet_get(packet)->queue_node, head);
+	return 0;
+}
+
+static int ssh_ptl_queue_push(struct ssh_packet *packet)
+{
+	int status;
+
+	spin_lock(&packet->ptl->queue.lock);
+	status = __ssh_ptl_queue_push(packet);
+	spin_unlock(&packet->ptl->queue.lock);
+
+	return status;
+}
+
+static void ssh_ptl_queue_remove(struct ssh_packet *packet)
+{
+	struct ssh_ptl *ptl = packet->ptl;
+
+	spin_lock(&ptl->queue.lock);
+
+	if (!test_and_clear_bit(SSH_PACKET_SF_QUEUED_BIT, &packet->state)) {
+		spin_unlock(&ptl->queue.lock);
+		return;
+	}
+
+	list_del(&packet->queue_node);
+
+	spin_unlock(&ptl->queue.lock);
+	ssh_packet_put(packet);
+}
+
+static void ssh_ptl_pending_push(struct ssh_packet *p)
+{
+	struct ssh_ptl *ptl = p->ptl;
+	const ktime_t timestamp = ktime_get_coarse_boottime();
+	const ktime_t timeout = ptl->rtx_timeout.timeout;
+
+	/*
+	 * Note: We can get the time for the timestamp before acquiring the
+	 * lock as this is the only place we're setting it and this function
+	 * is called only from the transmitter thread. Thus it is not possible
+	 * to overwrite the timestamp with an outdated value below.
+	 */
+
+	spin_lock(&ptl->pending.lock);
+
+	/* If we are canceling/completing this packet, do not add it. */
+	if (test_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state)) {
+		spin_unlock(&ptl->pending.lock);
+		return;
+	}
+
+	/*
+	 * On re-submission, the packet has already been added the pending
+	 * set. We still need to update the timestamp as the packet timeout is
+	 * reset for each (re-)submission.
+	 */
+	p->timestamp = timestamp;
+
+	/* In case it is already pending (e.g. re-submission), do not add it. */
+	if (!test_and_set_bit(SSH_PACKET_SF_PENDING_BIT, &p->state)) {
+		atomic_inc(&ptl->pending.count);
+		list_add_tail(&ssh_packet_get(p)->pending_node, &ptl->pending.head);
+	}
+
+	spin_unlock(&ptl->pending.lock);
+
+	/* Arm/update timeout reaper. */
+	ssh_ptl_timeout_reaper_mod(ptl, timestamp, timestamp + timeout);
+}
+
+static void ssh_ptl_pending_remove(struct ssh_packet *packet)
+{
+	struct ssh_ptl *ptl = packet->ptl;
+
+	spin_lock(&ptl->pending.lock);
+
+	if (!test_and_clear_bit(SSH_PACKET_SF_PENDING_BIT, &packet->state)) {
+		spin_unlock(&ptl->pending.lock);
+		return;
+	}
+
+	list_del(&packet->pending_node);
+	atomic_dec(&ptl->pending.count);
+
+	spin_unlock(&ptl->pending.lock);
+
+	ssh_packet_put(packet);
+}
+
+/* Warning: Does not check/set "completed" bit. */
+static void __ssh_ptl_complete(struct ssh_packet *p, int status)
+{
+	struct ssh_ptl *ptl = READ_ONCE(p->ptl);
+
+	trace_ssam_packet_complete(p, status);
+	ptl_dbg_cond(ptl, "ptl: completing packet %p (status: %d)\n", p, status);
+
+	if (p->ops->complete)
+		p->ops->complete(p, status);
+}
+
+static void ssh_ptl_remove_and_complete(struct ssh_packet *p, int status)
+{
+	/*
+	 * A call to this function should in general be preceded by
+	 * set_bit(SSH_PACKET_SF_LOCKED_BIT, &p->flags) to avoid re-adding the
+	 * packet to the structures it's going to be removed from.
+	 *
+	 * The set_bit call does not need explicit memory barriers as the
+	 * implicit barrier of the test_and_set_bit() call below ensure that the
+	 * flag is visible before we actually attempt to remove the packet.
+	 */
+
+	if (test_and_set_bit(SSH_PACKET_SF_COMPLETED_BIT, &p->state))
+		return;
+
+	ssh_ptl_queue_remove(p);
+	ssh_ptl_pending_remove(p);
+
+	__ssh_ptl_complete(p, status);
+}
+
+static bool ssh_ptl_tx_can_process(struct ssh_packet *packet)
+{
+	struct ssh_ptl *ptl = packet->ptl;
+
+	if (test_bit(SSH_PACKET_TY_FLUSH_BIT, &packet->state))
+		return !atomic_read(&ptl->pending.count);
+
+	/* We can always process non-blocking packets. */
+	if (!test_bit(SSH_PACKET_TY_BLOCKING_BIT, &packet->state))
+		return true;
+
+	/* If we are already waiting for this packet, send it again. */
+	if (test_bit(SSH_PACKET_SF_PENDING_BIT, &packet->state))
+		return true;
+
+	/* Otherwise: Check if we have the capacity to send. */
+	return atomic_read(&ptl->pending.count) < SSH_PTL_MAX_PENDING;
+}
+
+static struct ssh_packet *ssh_ptl_tx_pop(struct ssh_ptl *ptl)
+{
+	struct ssh_packet *packet = ERR_PTR(-ENOENT);
+	struct ssh_packet *p, *n;
+
+	spin_lock(&ptl->queue.lock);
+	list_for_each_entry_safe(p, n, &ptl->queue.head, queue_node) {
+		/*
+		 * If we are canceling or completing this packet, ignore it.
+		 * It's going to be removed from this queue shortly.
+		 */
+		if (test_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state))
+			continue;
+
+		/*
+		 * Packets should be ordered non-blocking/to-be-resent first.
+		 * If we cannot process this packet, assume that we can't
+		 * process any following packet either and abort.
+		 */
+		if (!ssh_ptl_tx_can_process(p)) {
+			packet = ERR_PTR(-EBUSY);
+			break;
+		}
+
+		/*
+		 * We are allowed to change the state now. Remove it from the
+		 * queue and mark it as being transmitted.
+		 */
+
+		list_del(&p->queue_node);
+
+		set_bit(SSH_PACKET_SF_TRANSMITTING_BIT, &p->state);
+		/* Ensure that state never gets zero. */
+		smp_mb__before_atomic();
+		clear_bit(SSH_PACKET_SF_QUEUED_BIT, &p->state);
+
+		/*
+		 * Update number of tries. This directly influences the
+		 * priority in case the packet is re-submitted (e.g. via
+		 * timeout/NAK). Note that all reads and writes to the
+		 * priority after the first submission are guarded by the
+		 * queue lock.
+		 */
+		ssh_packet_next_try(p);
+
+		packet = p;
+		break;
+	}
+	spin_unlock(&ptl->queue.lock);
+
+	return packet;
+}
+
+static struct ssh_packet *ssh_ptl_tx_next(struct ssh_ptl *ptl)
+{
+	struct ssh_packet *p;
+
+	p = ssh_ptl_tx_pop(ptl);
+	if (IS_ERR(p))
+		return p;
+
+	if (test_bit(SSH_PACKET_TY_SEQUENCED_BIT, &p->state)) {
+		ptl_dbg(ptl, "ptl: transmitting sequenced packet %p\n", p);
+		ssh_ptl_pending_push(p);
+	} else {
+		ptl_dbg(ptl, "ptl: transmitting non-sequenced packet %p\n", p);
+	}
+
+	return p;
+}
+
+static void ssh_ptl_tx_compl_success(struct ssh_packet *packet)
+{
+	struct ssh_ptl *ptl = packet->ptl;
+
+	ptl_dbg(ptl, "ptl: successfully transmitted packet %p\n", packet);
+
+	/* Transition state to "transmitted". */
+	set_bit(SSH_PACKET_SF_TRANSMITTED_BIT, &packet->state);
+	/* Ensure that state never gets zero. */
+	smp_mb__before_atomic();
+	clear_bit(SSH_PACKET_SF_TRANSMITTING_BIT, &packet->state);
+
+	/* If the packet is unsequenced, we're done: Lock and complete. */
+	if (!test_bit(SSH_PACKET_TY_SEQUENCED_BIT, &packet->state)) {
+		set_bit(SSH_PACKET_SF_LOCKED_BIT, &packet->state);
+		ssh_ptl_remove_and_complete(packet, 0);
+	}
+
+	/*
+	 * Notify that a packet transmission has finished. In general we're only
+	 * waiting for one packet (if any), so wake_up_all should be fine.
+	 */
+	wake_up_all(&ptl->tx.packet_wq);
+}
+
+static void ssh_ptl_tx_compl_error(struct ssh_packet *packet, int status)
+{
+	/* Transmission failure: Lock the packet and try to complete it. */
+	set_bit(SSH_PACKET_SF_LOCKED_BIT, &packet->state);
+	/* Ensure that state never gets zero. */
+	smp_mb__before_atomic();
+	clear_bit(SSH_PACKET_SF_TRANSMITTING_BIT, &packet->state);
+
+	ptl_err(packet->ptl, "ptl: transmission error: %d\n", status);
+	ptl_dbg(packet->ptl, "ptl: failed to transmit packet: %p\n", packet);
+
+	ssh_ptl_remove_and_complete(packet, status);
+
+	/*
+	 * Notify that a packet transmission has finished. In general we're only
+	 * waiting for one packet (if any), so wake_up_all should be fine.
+	 */
+	wake_up_all(&packet->ptl->tx.packet_wq);
+}
+
+static long ssh_ptl_tx_wait_packet(struct ssh_ptl *ptl)
+{
+	int status;
+
+	status = wait_for_completion_interruptible(&ptl->tx.thread_cplt_pkt);
+	reinit_completion(&ptl->tx.thread_cplt_pkt);
+
+	/*
+	 * Ensure completion is cleared before continuing to avoid lost update
+	 * problems.
+	 */
+	smp_mb__after_atomic();
+
+	return status;
+}
+
+static long ssh_ptl_tx_wait_transfer(struct ssh_ptl *ptl, long timeout)
+{
+	long status;
+
+	status = wait_for_completion_interruptible_timeout(&ptl->tx.thread_cplt_tx,
+							   timeout);
+	reinit_completion(&ptl->tx.thread_cplt_tx);
+
+	/*
+	 * Ensure completion is cleared before continuing to avoid lost update
+	 * problems.
+	 */
+	smp_mb__after_atomic();
+
+	return status;
+}
+
+static int ssh_ptl_tx_packet(struct ssh_ptl *ptl, struct ssh_packet *packet)
+{
+	long timeout = SSH_PTL_TX_TIMEOUT;
+	size_t offset = 0;
+
+	/* Note: Flush-packets don't have any data. */
+	if (unlikely(!packet->data.ptr))
+		return 0;
+
+	/* Error injection: drop packet to simulate transmission problem. */
+	if (ssh_ptl_should_drop_packet(packet))
+		return 0;
+
+	/* Error injection: simulate invalid packet data. */
+	ssh_ptl_tx_inject_invalid_data(packet);
+
+	ptl_dbg(ptl, "tx: sending data (length: %zu)\n", packet->data.len);
+	print_hex_dump_debug("tx: ", DUMP_PREFIX_OFFSET, 16, 1,
+			     packet->data.ptr, packet->data.len, false);
+
+	do {
+		ssize_t status, len;
+		u8 *buf;
+
+		buf = packet->data.ptr + offset;
+		len = packet->data.len - offset;
+
+		status = ssh_ptl_write_buf(ptl, packet, buf, len);
+		if (status < 0)
+			return status;
+
+		if (status == len)
+			return 0;
+
+		offset += status;
+
+		timeout = ssh_ptl_tx_wait_transfer(ptl, timeout);
+		if (kthread_should_stop() || !atomic_read(&ptl->tx.running))
+			return -ESHUTDOWN;
+
+		if (timeout < 0)
+			return -EINTR;
+
+		if (timeout == 0)
+			return -ETIMEDOUT;
+	} while (true);
+}
+
+static int ssh_ptl_tx_threadfn(void *data)
+{
+	struct ssh_ptl *ptl = data;
+
+	while (!kthread_should_stop() && atomic_read(&ptl->tx.running)) {
+		struct ssh_packet *packet;
+		int status;
+
+		/* Try to get the next packet. */
+		packet = ssh_ptl_tx_next(ptl);
+
+		/* If no packet can be processed, we are done. */
+		if (IS_ERR(packet)) {
+			ssh_ptl_tx_wait_packet(ptl);
+			continue;
+		}
+
+		/* Transfer and complete packet. */
+		status = ssh_ptl_tx_packet(ptl, packet);
+		if (status)
+			ssh_ptl_tx_compl_error(packet, status);
+		else
+			ssh_ptl_tx_compl_success(packet);
+
+		ssh_packet_put(packet);
+	}
+
+	return 0;
+}
+
+/**
+ * ssh_ptl_tx_wakeup_packet() - Wake up packet transmitter thread for new
+ * packet.
+ * @ptl: The packet transport layer.
+ *
+ * Wakes up the packet transmitter thread, notifying it that a new packet has
+ * arrived and is ready for transfer. If the packet transport layer has been
+ * shut down, calls to this function will be ignored.
+ */
+static void ssh_ptl_tx_wakeup_packet(struct ssh_ptl *ptl)
+{
+	if (test_bit(SSH_PTL_SF_SHUTDOWN_BIT, &ptl->state))
+		return;
+
+	complete(&ptl->tx.thread_cplt_pkt);
+}
+
+/**
+ * ssh_ptl_tx_start() - Start packet transmitter thread.
+ * @ptl: The packet transport layer.
+ *
+ * Return: Returns zero on success, a negative error code on failure.
+ */
+int ssh_ptl_tx_start(struct ssh_ptl *ptl)
+{
+	atomic_set_release(&ptl->tx.running, 1);
+
+	ptl->tx.thread = kthread_run(ssh_ptl_tx_threadfn, ptl, "ssam_serial_hub-tx");
+	if (IS_ERR(ptl->tx.thread))
+		return PTR_ERR(ptl->tx.thread);
+
+	return 0;
+}
+
+/**
+ * ssh_ptl_tx_stop() - Stop packet transmitter thread.
+ * @ptl: The packet transport layer.
+ *
+ * Return: Returns zero on success, a negative error code on failure.
+ */
+int ssh_ptl_tx_stop(struct ssh_ptl *ptl)
+{
+	int status = 0;
+
+	if (!IS_ERR_OR_NULL(ptl->tx.thread)) {
+		/* Tell thread to stop. */
+		atomic_set_release(&ptl->tx.running, 0);
+
+		/*
+		 * Wake up thread in case it is paused. Do not use wakeup
+		 * helpers as this may be called when the shutdown bit has
+		 * already been set.
+		 */
+		complete(&ptl->tx.thread_cplt_pkt);
+		complete(&ptl->tx.thread_cplt_tx);
+
+		/* Finally, wait for thread to stop. */
+		status = kthread_stop(ptl->tx.thread);
+		ptl->tx.thread = NULL;
+	}
+
+	return status;
+}
+
+static struct ssh_packet *ssh_ptl_ack_pop(struct ssh_ptl *ptl, u8 seq_id)
+{
+	struct ssh_packet *packet = ERR_PTR(-ENOENT);
+	struct ssh_packet *p, *n;
+
+	spin_lock(&ptl->pending.lock);
+	list_for_each_entry_safe(p, n, &ptl->pending.head, pending_node) {
+		/*
+		 * We generally expect packets to be in order, so first packet
+		 * to be added to pending is first to be sent, is first to be
+		 * ACKed.
+		 */
+		if (unlikely(ssh_packet_get_seq(p) != seq_id))
+			continue;
+
+		/*
+		 * In case we receive an ACK while handling a transmission
+		 * error completion. The packet will be removed shortly.
+		 */
+		if (unlikely(test_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state))) {
+			packet = ERR_PTR(-EPERM);
+			break;
+		}
+
+		/*
+		 * Mark the packet as ACKed and remove it from pending by
+		 * removing its node and decrementing the pending counter.
+		 */
+		set_bit(SSH_PACKET_SF_ACKED_BIT, &p->state);
+		/* Ensure that state never gets zero. */
+		smp_mb__before_atomic();
+		clear_bit(SSH_PACKET_SF_PENDING_BIT, &p->state);
+
+		atomic_dec(&ptl->pending.count);
+		list_del(&p->pending_node);
+		packet = p;
+
+		break;
+	}
+	spin_unlock(&ptl->pending.lock);
+
+	return packet;
+}
+
+static void ssh_ptl_wait_until_transmitted(struct ssh_packet *packet)
+{
+	wait_event(packet->ptl->tx.packet_wq,
+		   test_bit(SSH_PACKET_SF_TRANSMITTED_BIT, &packet->state) ||
+		   test_bit(SSH_PACKET_SF_LOCKED_BIT, &packet->state));
+}
+
+static void ssh_ptl_acknowledge(struct ssh_ptl *ptl, u8 seq)
+{
+	struct ssh_packet *p;
+
+	p = ssh_ptl_ack_pop(ptl, seq);
+	if (IS_ERR(p)) {
+		if (PTR_ERR(p) == -ENOENT) {
+			/*
+			 * The packet has not been found in the set of pending
+			 * packets.
+			 */
+			ptl_warn(ptl, "ptl: received ACK for non-pending packet\n");
+		} else {
+			/*
+			 * The packet is pending, but we are not allowed to take
+			 * it because it has been locked.
+			 */
+			WARN_ON(PTR_ERR(p) != -EPERM);
+		}
+		return;
+	}
+
+	ptl_dbg(ptl, "ptl: received ACK for packet %p\n", p);
+
+	/*
+	 * It is possible that the packet has been transmitted, but the state
+	 * has not been updated from "transmitting" to "transmitted" yet.
+	 * In that case, we need to wait for this transition to occur in order
+	 * to determine between success or failure.
+	 *
+	 * On transmission failure, the packet will be locked after this call.
+	 * On success, the transmitted bit will be set.
+	 */
+	ssh_ptl_wait_until_transmitted(p);
+
+	/*
+	 * The packet will already be locked in case of a transmission error or
+	 * cancellation. Let the transmitter or cancellation issuer complete the
+	 * packet.
+	 */
+	if (unlikely(test_and_set_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state))) {
+		if (unlikely(!test_bit(SSH_PACKET_SF_TRANSMITTED_BIT, &p->state)))
+			ptl_err(ptl, "ptl: received ACK before packet had been fully transmitted\n");
+
+		ssh_packet_put(p);
+		return;
+	}
+
+	ssh_ptl_remove_and_complete(p, 0);
+	ssh_packet_put(p);
+
+	if (atomic_read(&ptl->pending.count) < SSH_PTL_MAX_PENDING)
+		ssh_ptl_tx_wakeup_packet(ptl);
+}
+
+/**
+ * ssh_ptl_submit() - Submit a packet to the transport layer.
+ * @ptl: The packet transport layer to submit the packet to.
+ * @p:   The packet to submit.
+ *
+ * Submits a new packet to the transport layer, queuing it to be sent. This
+ * function should not be used for re-submission.
+ *
+ * Return: Returns zero on success, %-EINVAL if a packet field is invalid or
+ * the packet has been canceled prior to submission, %-EALREADY if the packet
+ * has already been submitted, or %-ESHUTDOWN if the packet transport layer
+ * has been shut down.
+ */
+int ssh_ptl_submit(struct ssh_ptl *ptl, struct ssh_packet *p)
+{
+	struct ssh_ptl *ptl_old;
+	int status;
+
+	trace_ssam_packet_submit(p);
+
+	/* Validate packet fields. */
+	if (test_bit(SSH_PACKET_TY_FLUSH_BIT, &p->state)) {
+		if (p->data.ptr || test_bit(SSH_PACKET_TY_SEQUENCED_BIT, &p->state))
+			return -EINVAL;
+	} else if (!p->data.ptr) {
+		return -EINVAL;
+	}
+
+	/*
+	 * The ptl reference only gets set on or before the first submission.
+	 * After the first submission, it has to be read-only.
+	 *
+	 * Note that ptl may already be set from upper-layer request
+	 * submission, thus we cannot expect it to be NULL.
+	 */
+	ptl_old = READ_ONCE(p->ptl);
+	if (!ptl_old)
+		WRITE_ONCE(p->ptl, ptl);
+	else if (WARN_ON(ptl_old != ptl))
+		return -EALREADY;	/* Submitted on different PTL. */
+
+	status = ssh_ptl_queue_push(p);
+	if (status)
+		return status;
+
+	if (!test_bit(SSH_PACKET_TY_BLOCKING_BIT, &p->state) ||
+	    (atomic_read(&ptl->pending.count) < SSH_PTL_MAX_PENDING))
+		ssh_ptl_tx_wakeup_packet(ptl);
+
+	return 0;
+}
+
+/*
+ * __ssh_ptl_resubmit() - Re-submit a packet to the transport layer.
+ * @packet: The packet to re-submit.
+ *
+ * Re-submits the given packet: Checks if it can be re-submitted and queues it
+ * if it can, resetting the packet timestamp in the process. Must be called
+ * with the pending lock held.
+ *
+ * Return: Returns %-ECANCELED if the packet has exceeded its number of tries,
+ * %-EINVAL if the packet has been locked, %-EALREADY if the packet is already
+ * on the queue, and %-ESHUTDOWN if the transmission layer has been shut down.
+ */
+static int __ssh_ptl_resubmit(struct ssh_packet *packet)
+{
+	int status;
+	u8 try;
+
+	lockdep_assert_held(&packet->ptl->pending.lock);
+
+	trace_ssam_packet_resubmit(packet);
+
+	spin_lock(&packet->ptl->queue.lock);
+
+	/* Check if the packet is out of tries. */
+	try = ssh_packet_priority_get_try(packet->priority);
+	if (try >= SSH_PTL_MAX_PACKET_TRIES) {
+		spin_unlock(&packet->ptl->queue.lock);
+		return -ECANCELED;
+	}
+
+	status = __ssh_ptl_queue_push(packet);
+	if (status) {
+		/*
+		 * An error here indicates that the packet has either already
+		 * been queued, been locked, or the transport layer is being
+		 * shut down. In all cases: Ignore the error.
+		 */
+		spin_unlock(&packet->ptl->queue.lock);
+		return status;
+	}
+
+	packet->timestamp = KTIME_MAX;
+
+	spin_unlock(&packet->ptl->queue.lock);
+	return 0;
+}
+
+static void ssh_ptl_resubmit_pending(struct ssh_ptl *ptl)
+{
+	struct ssh_packet *p;
+	bool resub = false;
+
+	/*
+	 * Note: We deliberately do not remove/attempt to cancel and complete
+	 * packets that are out of tires in this function. The packet will be
+	 * eventually canceled and completed by the timeout. Removing the packet
+	 * here could lead to overly eager cancellation if the packet has not
+	 * been re-transmitted yet but the tries-counter already updated (i.e
+	 * ssh_ptl_tx_next() removed the packet from the queue and updated the
+	 * counter, but re-transmission for the last try has not actually
+	 * started yet).
+	 */
+
+	spin_lock(&ptl->pending.lock);
+
+	/* Re-queue all pending packets. */
+	list_for_each_entry(p, &ptl->pending.head, pending_node) {
+		/*
+		 * Re-submission fails if the packet is out of tries, has been
+		 * locked, is already queued, or the layer is being shut down.
+		 * No need to re-schedule tx-thread in those cases.
+		 */
+		if (!__ssh_ptl_resubmit(p))
+			resub = true;
+	}
+
+	spin_unlock(&ptl->pending.lock);
+
+	if (resub)
+		ssh_ptl_tx_wakeup_packet(ptl);
+}
+
+/**
+ * ssh_ptl_cancel() - Cancel a packet.
+ * @p: The packet to cancel.
+ *
+ * Cancels a packet. There are no guarantees on when completion and release
+ * callbacks will be called. This may occur during execution of this function
+ * or may occur at any point later.
+ *
+ * Note that it is not guaranteed that the packet will actually be canceled if
+ * the packet is concurrently completed by another process. The only guarantee
+ * of this function is that the packet will be completed (with success,
+ * failure, or cancellation) and released from the transport layer in a
+ * reasonable time-frame.
+ *
+ * May be called before the packet has been submitted, in which case any later
+ * packet submission fails.
+ */
+void ssh_ptl_cancel(struct ssh_packet *p)
+{
+	if (test_and_set_bit(SSH_PACKET_SF_CANCELED_BIT, &p->state))
+		return;
+
+	trace_ssam_packet_cancel(p);
+
+	/*
+	 * Lock packet and commit with memory barrier. If this packet has
+	 * already been locked, it's going to be removed and completed by
+	 * another party, which should have precedence.
+	 */
+	if (test_and_set_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state))
+		return;
+
+	/*
+	 * By marking the packet as locked and employing the implicit memory
+	 * barrier of test_and_set_bit, we have guaranteed that, at this point,
+	 * the packet cannot be added to the queue any more.
+	 *
+	 * In case the packet has never been submitted, packet->ptl is NULL. If
+	 * the packet is currently being submitted, packet->ptl may be NULL or
+	 * non-NULL. Due marking the packet as locked above and committing with
+	 * the memory barrier, we have guaranteed that, if packet->ptl is NULL,
+	 * the packet will never be added to the queue. If packet->ptl is
+	 * non-NULL, we don't have any guarantees.
+	 */
+
+	if (READ_ONCE(p->ptl)) {
+		ssh_ptl_remove_and_complete(p, -ECANCELED);
+
+		if (atomic_read(&p->ptl->pending.count) < SSH_PTL_MAX_PENDING)
+			ssh_ptl_tx_wakeup_packet(p->ptl);
+
+	} else if (!test_and_set_bit(SSH_PACKET_SF_COMPLETED_BIT, &p->state)) {
+		__ssh_ptl_complete(p, -ECANCELED);
+	}
+}
+
+/* Must be called with pending lock held */
+static ktime_t ssh_packet_get_expiration(struct ssh_packet *p, ktime_t timeout)
+{
+	lockdep_assert_held(&p->ptl->pending.lock);
+
+	if (p->timestamp != KTIME_MAX)
+		return ktime_add(p->timestamp, timeout);
+	else
+		return KTIME_MAX;
+}
+
+static void ssh_ptl_timeout_reap(struct work_struct *work)
+{
+	struct ssh_ptl *ptl = to_ssh_ptl(work, rtx_timeout.reaper.work);
+	struct ssh_packet *p, *n;
+	LIST_HEAD(claimed);
+	ktime_t now = ktime_get_coarse_boottime();
+	ktime_t timeout = ptl->rtx_timeout.timeout;
+	ktime_t next = KTIME_MAX;
+	bool resub = false;
+	int status;
+
+	trace_ssam_ptl_timeout_reap(atomic_read(&ptl->pending.count));
+
+	/*
+	 * Mark reaper as "not pending". This is done before checking any
+	 * packets to avoid lost-update type problems.
+	 */
+	spin_lock(&ptl->rtx_timeout.lock);
+	ptl->rtx_timeout.expires = KTIME_MAX;
+	spin_unlock(&ptl->rtx_timeout.lock);
+
+	spin_lock(&ptl->pending.lock);
+
+	list_for_each_entry_safe(p, n, &ptl->pending.head, pending_node) {
+		ktime_t expires = ssh_packet_get_expiration(p, timeout);
+
+		/*
+		 * Check if the timeout hasn't expired yet. Find out next
+		 * expiration date to be handled after this run.
+		 */
+		if (ktime_after(expires, now)) {
+			next = ktime_before(expires, next) ? expires : next;
+			continue;
+		}
+
+		trace_ssam_packet_timeout(p);
+
+		status = __ssh_ptl_resubmit(p);
+
+		/*
+		 * Re-submission fails if the packet is out of tries, has been
+		 * locked, is already queued, or the layer is being shut down.
+		 * No need to re-schedule tx-thread in those cases.
+		 */
+		if (!status)
+			resub = true;
+
+		/* Go to next packet if this packet is not out of tries. */
+		if (status != -ECANCELED)
+			continue;
+
+		/* No more tries left: Cancel the packet. */
+
+		/*
+		 * If someone else has locked the packet already, don't use it
+		 * and let the other party complete it.
+		 */
+		if (test_and_set_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state))
+			continue;
+
+		/*
+		 * We have now marked the packet as locked. Thus it cannot be
+		 * added to the pending list again after we've removed it here.
+		 * We can therefore re-use the pending_node of this packet
+		 * temporarily.
+		 */
+
+		clear_bit(SSH_PACKET_SF_PENDING_BIT, &p->state);
+
+		atomic_dec(&ptl->pending.count);
+		list_move_tail(&p->pending_node, &claimed);
+	}
+
+	spin_unlock(&ptl->pending.lock);
+
+	/* Cancel and complete the packet. */
+	list_for_each_entry_safe(p, n, &claimed, pending_node) {
+		if (!test_and_set_bit(SSH_PACKET_SF_COMPLETED_BIT, &p->state)) {
+			ssh_ptl_queue_remove(p);
+			__ssh_ptl_complete(p, -ETIMEDOUT);
+		}
+
+		/*
+		 * Drop the reference we've obtained by removing it from
+		 * the pending set.
+		 */
+		list_del(&p->pending_node);
+		ssh_packet_put(p);
+	}
+
+	/* Ensure that reaper doesn't run again immediately. */
+	next = max(next, ktime_add(now, SSH_PTL_PACKET_TIMEOUT_RESOLUTION));
+	if (next != KTIME_MAX)
+		ssh_ptl_timeout_reaper_mod(ptl, now, next);
+
+	if (resub)
+		ssh_ptl_tx_wakeup_packet(ptl);
+}
+
+static bool ssh_ptl_rx_retransmit_check(struct ssh_ptl *ptl, const struct ssh_frame *frame)
+{
+	int i;
+
+	/*
+	 * Ignore unsequenced packets. On some devices (notably Surface Pro 9),
+	 * unsequenced events will always be sent with SEQ=0x00. Attempting to
+	 * detect retransmission would thus just block all events.
+	 *
+	 * While sequence numbers would also allow detection of retransmitted
+	 * packets in unsequenced communication, they have only ever been used
+	 * to cover edge-cases in sequenced transmission. In particular, the
+	 * only instance of packets being retransmitted (that we are aware of)
+	 * is due to an ACK timeout. As this does not happen in unsequenced
+	 * communication, skip the retransmission check for those packets
+	 * entirely.
+	 */
+	if (frame->type == SSH_FRAME_TYPE_DATA_NSQ)
+		return false;
+
+	/*
+	 * Check if SEQ has been seen recently (i.e. packet was
+	 * re-transmitted and we should ignore it).
+	 */
+	for (i = 0; i < ARRAY_SIZE(ptl->rx.blocked.seqs); i++) {
+		if (likely(ptl->rx.blocked.seqs[i] != frame->seq))
+			continue;
+
+		ptl_dbg(ptl, "ptl: ignoring repeated data packet\n");
+		return true;
+	}
+
+	/* Update list of blocked sequence IDs. */
+	ptl->rx.blocked.seqs[ptl->rx.blocked.offset] = frame->seq;
+	ptl->rx.blocked.offset = (ptl->rx.blocked.offset + 1)
+				  % ARRAY_SIZE(ptl->rx.blocked.seqs);
+
+	return false;
+}
+
+static void ssh_ptl_rx_dataframe(struct ssh_ptl *ptl,
+				 const struct ssh_frame *frame,
+				 const struct ssam_span *payload)
+{
+	if (ssh_ptl_rx_retransmit_check(ptl, frame))
+		return;
+
+	ptl->ops.data_received(ptl, payload);
+}
+
+static void ssh_ptl_send_ack(struct ssh_ptl *ptl, u8 seq)
+{
+	struct ssh_packet *packet;
+	struct ssam_span buf;
+	struct msgbuf msgb;
+	int status;
+
+	status = ssh_ctrl_packet_alloc(&packet, &buf, GFP_KERNEL);
+	if (status) {
+		ptl_err(ptl, "ptl: failed to allocate ACK packet\n");
+		return;
+	}
+
+	ssh_packet_init(packet, 0, SSH_PACKET_PRIORITY(ACK, 0),
+			&ssh_ptl_ctrl_packet_ops);
+
+	msgb_init(&msgb, buf.ptr, buf.len);
+	msgb_push_ack(&msgb, seq);
+	ssh_packet_set_data(packet, msgb.begin, msgb_bytes_used(&msgb));
+
+	ssh_ptl_submit(ptl, packet);
+	ssh_packet_put(packet);
+}
+
+static void ssh_ptl_send_nak(struct ssh_ptl *ptl)
+{
+	struct ssh_packet *packet;
+	struct ssam_span buf;
+	struct msgbuf msgb;
+	int status;
+
+	status = ssh_ctrl_packet_alloc(&packet, &buf, GFP_KERNEL);
+	if (status) {
+		ptl_err(ptl, "ptl: failed to allocate NAK packet\n");
+		return;
+	}
+
+	ssh_packet_init(packet, 0, SSH_PACKET_PRIORITY(NAK, 0),
+			&ssh_ptl_ctrl_packet_ops);
+
+	msgb_init(&msgb, buf.ptr, buf.len);
+	msgb_push_nak(&msgb);
+	ssh_packet_set_data(packet, msgb.begin, msgb_bytes_used(&msgb));
+
+	ssh_ptl_submit(ptl, packet);
+	ssh_packet_put(packet);
+}
+
+static size_t ssh_ptl_rx_eval(struct ssh_ptl *ptl, struct ssam_span *source)
+{
+	struct ssh_frame *frame;
+	struct ssam_span payload;
+	struct ssam_span aligned;
+	bool syn_found;
+	int status;
+
+	/* Error injection: Modify data to simulate corrupt SYN bytes. */
+	ssh_ptl_rx_inject_invalid_syn(ptl, source);
+
+	/* Find SYN. */
+	syn_found = sshp_find_syn(source, &aligned);
+
+	if (unlikely(aligned.ptr != source->ptr)) {
+		/*
+		 * We expect aligned.ptr == source->ptr. If this is not the
+		 * case, then aligned.ptr > source->ptr and we've encountered
+		 * some unexpected data where we'd expect the start of a new
+		 * message (i.e. the SYN sequence).
+		 *
+		 * This can happen when a CRC check for the previous message
+		 * failed and we start actively searching for the next one
+		 * (via the call to sshp_find_syn() above), or the first bytes
+		 * of a message got dropped or corrupted.
+		 *
+		 * In any case, we issue a warning, send a NAK to the EC to
+		 * request re-transmission of any data we haven't acknowledged
+		 * yet, and finally, skip everything up to the next SYN
+		 * sequence.
+		 */
+
+		ptl_warn(ptl, "rx: parser: invalid start of frame, skipping\n");
+
+		/*
+		 * Notes:
+		 * - This might send multiple NAKs in case the communication
+		 *   starts with an invalid SYN and is broken down into multiple
+		 *   pieces. This should generally be handled fine, we just
+		 *   might receive duplicate data in this case, which is
+		 *   detected when handling data frames.
+		 * - This path will also be executed on invalid CRCs: When an
+		 *   invalid CRC is encountered, the code below will skip data
+		 *   until directly after the SYN. This causes the search for
+		 *   the next SYN, which is generally not placed directly after
+		 *   the last one.
+		 *
+		 *   Open question: Should we send this in case of invalid
+		 *   payload CRCs if the frame-type is non-sequential (current
+		 *   implementation) or should we drop that frame without
+		 *   telling the EC?
+		 */
+		ssh_ptl_send_nak(ptl);
+	}
+
+	if (unlikely(!syn_found))
+		return aligned.ptr - source->ptr;
+
+	/* Error injection: Modify data to simulate corruption. */
+	ssh_ptl_rx_inject_invalid_data(ptl, &aligned);
+
+	/* Parse and validate frame. */
+	status = sshp_parse_frame(&ptl->serdev->dev, &aligned, &frame, &payload,
+				  SSH_PTL_RX_BUF_LEN);
+	if (status)	/* Invalid frame: skip to next SYN. */
+		return aligned.ptr - source->ptr + sizeof(u16);
+	if (!frame)	/* Not enough data. */
+		return aligned.ptr - source->ptr;
+
+	trace_ssam_rx_frame_received(frame);
+
+	switch (frame->type) {
+	case SSH_FRAME_TYPE_ACK:
+		ssh_ptl_acknowledge(ptl, frame->seq);
+		break;
+
+	case SSH_FRAME_TYPE_NAK:
+		ssh_ptl_resubmit_pending(ptl);
+		break;
+
+	case SSH_FRAME_TYPE_DATA_SEQ:
+		ssh_ptl_send_ack(ptl, frame->seq);
+		fallthrough;
+
+	case SSH_FRAME_TYPE_DATA_NSQ:
+		ssh_ptl_rx_dataframe(ptl, frame, &payload);
+		break;
+
+	default:
+		ptl_warn(ptl, "ptl: received frame with unknown type %#04x\n",
+			 frame->type);
+		break;
+	}
+
+	return aligned.ptr - source->ptr + SSH_MESSAGE_LENGTH(payload.len);
+}
+
+static int ssh_ptl_rx_threadfn(void *data)
+{
+	struct ssh_ptl *ptl = data;
+
+	while (true) {
+		struct ssam_span span;
+		size_t offs = 0;
+		size_t n;
+
+		wait_event_interruptible(ptl->rx.wq,
+					 !kfifo_is_empty(&ptl->rx.fifo) ||
+					 kthread_should_stop());
+		if (kthread_should_stop())
+			break;
+
+		/* Copy from fifo to evaluation buffer. */
+		n = sshp_buf_read_from_fifo(&ptl->rx.buf, &ptl->rx.fifo);
+
+		ptl_dbg(ptl, "rx: received data (size: %zu)\n", n);
+		print_hex_dump_debug("rx: ", DUMP_PREFIX_OFFSET, 16, 1,
+				     ptl->rx.buf.ptr + ptl->rx.buf.len - n,
+				     n, false);
+
+		/* Parse until we need more bytes or buffer is empty. */
+		while (offs < ptl->rx.buf.len) {
+			sshp_buf_span_from(&ptl->rx.buf, offs, &span);
+			n = ssh_ptl_rx_eval(ptl, &span);
+			if (n == 0)
+				break;	/* Need more bytes. */
+
+			offs += n;
+		}
+
+		/* Throw away the evaluated parts. */
+		sshp_buf_drop(&ptl->rx.buf, offs);
+	}
+
+	return 0;
+}
+
+static void ssh_ptl_rx_wakeup(struct ssh_ptl *ptl)
+{
+	wake_up(&ptl->rx.wq);
+}
+
+/**
+ * ssh_ptl_rx_start() - Start packet transport layer receiver thread.
+ * @ptl: The packet transport layer.
+ *
+ * Return: Returns zero on success, a negative error code on failure.
+ */
+int ssh_ptl_rx_start(struct ssh_ptl *ptl)
+{
+	if (ptl->rx.thread)
+		return 0;
+
+	ptl->rx.thread = kthread_run(ssh_ptl_rx_threadfn, ptl,
+				     "ssam_serial_hub-rx");
+	if (IS_ERR(ptl->rx.thread))
+		return PTR_ERR(ptl->rx.thread);
+
+	return 0;
+}
+
+/**
+ * ssh_ptl_rx_stop() - Stop packet transport layer receiver thread.
+ * @ptl: The packet transport layer.
+ *
+ * Return: Returns zero on success, a negative error code on failure.
+ */
+int ssh_ptl_rx_stop(struct ssh_ptl *ptl)
+{
+	int status = 0;
+
+	if (ptl->rx.thread) {
+		status = kthread_stop(ptl->rx.thread);
+		ptl->rx.thread = NULL;
+	}
+
+	return status;
+}
+
+/**
+ * ssh_ptl_rx_rcvbuf() - Push data from lower-layer transport to the packet
+ * layer.
+ * @ptl: The packet transport layer.
+ * @buf: Pointer to the data to push to the layer.
+ * @n:   Size of the data to push to the layer, in bytes.
+ *
+ * Pushes data from a lower-layer transport to the receiver fifo buffer of the
+ * packet layer and notifies the receiver thread. Calls to this function are
+ * ignored once the packet layer has been shut down.
+ *
+ * Return: Returns the number of bytes transferred (positive or zero) on
+ * success. Returns %-ESHUTDOWN if the packet layer has been shut down.
+ */
+int ssh_ptl_rx_rcvbuf(struct ssh_ptl *ptl, const u8 *buf, size_t n)
+{
+	int used;
+
+	if (test_bit(SSH_PTL_SF_SHUTDOWN_BIT, &ptl->state))
+		return -ESHUTDOWN;
+
+	used = kfifo_in(&ptl->rx.fifo, buf, n);
+	if (used)
+		ssh_ptl_rx_wakeup(ptl);
+
+	return used;
+}
+
+/**
+ * ssh_ptl_shutdown() - Shut down the packet transport layer.
+ * @ptl: The packet transport layer.
+ *
+ * Shuts down the packet transport layer, removing and canceling all queued
+ * and pending packets. Packets canceled by this operation will be completed
+ * with %-ESHUTDOWN as status. Receiver and transmitter threads will be
+ * stopped.
+ *
+ * As a result of this function, the transport layer will be marked as shut
+ * down. Submission of packets after the transport layer has been shut down
+ * will fail with %-ESHUTDOWN.
+ */
+void ssh_ptl_shutdown(struct ssh_ptl *ptl)
+{
+	LIST_HEAD(complete_q);
+	LIST_HEAD(complete_p);
+	struct ssh_packet *p, *n;
+	int status;
+
+	/* Ensure that no new packets (including ACK/NAK) can be submitted. */
+	set_bit(SSH_PTL_SF_SHUTDOWN_BIT, &ptl->state);
+	/*
+	 * Ensure that the layer gets marked as shut-down before actually
+	 * stopping it. In combination with the check in ssh_ptl_queue_push(),
+	 * this guarantees that no new packets can be added and all already
+	 * queued packets are properly canceled. In combination with the check
+	 * in ssh_ptl_rx_rcvbuf(), this guarantees that received data is
+	 * properly cut off.
+	 */
+	smp_mb__after_atomic();
+
+	status = ssh_ptl_rx_stop(ptl);
+	if (status)
+		ptl_err(ptl, "ptl: failed to stop receiver thread\n");
+
+	status = ssh_ptl_tx_stop(ptl);
+	if (status)
+		ptl_err(ptl, "ptl: failed to stop transmitter thread\n");
+
+	cancel_delayed_work_sync(&ptl->rtx_timeout.reaper);
+
+	/*
+	 * At this point, all threads have been stopped. This means that the
+	 * only references to packets from inside the system are in the queue
+	 * and pending set.
+	 *
+	 * Note: We still need locks here because someone could still be
+	 * canceling packets.
+	 *
+	 * Note 2: We can re-use queue_node (or pending_node) if we mark the
+	 * packet as locked an then remove it from the queue (or pending set
+	 * respectively). Marking the packet as locked avoids re-queuing
+	 * (which should already be prevented by having stopped the treads...)
+	 * and not setting QUEUED_BIT (or PENDING_BIT) prevents removal from a
+	 * new list via other threads (e.g. cancellation).
+	 *
+	 * Note 3: There may be overlap between complete_p and complete_q.
+	 * This is handled via test_and_set_bit() on the "completed" flag
+	 * (also handles cancellation).
+	 */
+
+	/* Mark queued packets as locked and move them to complete_q. */
+	spin_lock(&ptl->queue.lock);
+	list_for_each_entry_safe(p, n, &ptl->queue.head, queue_node) {
+		set_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state);
+		/* Ensure that state does not get zero. */
+		smp_mb__before_atomic();
+		clear_bit(SSH_PACKET_SF_QUEUED_BIT, &p->state);
+
+		list_move_tail(&p->queue_node, &complete_q);
+	}
+	spin_unlock(&ptl->queue.lock);
+
+	/* Mark pending packets as locked and move them to complete_p. */
+	spin_lock(&ptl->pending.lock);
+	list_for_each_entry_safe(p, n, &ptl->pending.head, pending_node) {
+		set_bit(SSH_PACKET_SF_LOCKED_BIT, &p->state);
+		/* Ensure that state does not get zero. */
+		smp_mb__before_atomic();
+		clear_bit(SSH_PACKET_SF_PENDING_BIT, &p->state);
+
+		list_move_tail(&p->pending_node, &complete_q);
+	}
+	atomic_set(&ptl->pending.count, 0);
+	spin_unlock(&ptl->pending.lock);
+
+	/* Complete and drop packets on complete_q. */
+	list_for_each_entry(p, &complete_q, queue_node) {
+		if (!test_and_set_bit(SSH_PACKET_SF_COMPLETED_BIT, &p->state))
+			__ssh_ptl_complete(p, -ESHUTDOWN);
+
+		ssh_packet_put(p);
+	}
+
+	/* Complete and drop packets on complete_p. */
+	list_for_each_entry(p, &complete_p, pending_node) {
+		if (!test_and_set_bit(SSH_PACKET_SF_COMPLETED_BIT, &p->state))
+			__ssh_ptl_complete(p, -ESHUTDOWN);
+
+		ssh_packet_put(p);
+	}
+
+	/*
+	 * At this point we have guaranteed that the system doesn't reference
+	 * any packets any more.
+	 */
+}
+
+/**
+ * ssh_ptl_init() - Initialize packet transport layer.
+ * @ptl:    The packet transport layer to initialize.
+ * @serdev: The underlying serial device, i.e. the lower-level transport.
+ * @ops:    Packet layer operations.
+ *
+ * Initializes the given packet transport layer. Transmitter and receiver
+ * threads must be started separately via ssh_ptl_tx_start() and
+ * ssh_ptl_rx_start(), after the packet-layer has been initialized and the
+ * lower-level transport layer has been set up.
+ *
+ * Return: Returns zero on success and a nonzero error code on failure.
+ */
+int ssh_ptl_init(struct ssh_ptl *ptl, struct serdev_device *serdev,
+		 struct ssh_ptl_ops *ops)
+{
+	int i, status;
+
+	ptl->serdev = serdev;
+	ptl->state = 0;
+
+	spin_lock_init(&ptl->queue.lock);
+	INIT_LIST_HEAD(&ptl->queue.head);
+
+	spin_lock_init(&ptl->pending.lock);
+	INIT_LIST_HEAD(&ptl->pending.head);
+	atomic_set_release(&ptl->pending.count, 0);
+
+	ptl->tx.thread = NULL;
+	atomic_set(&ptl->tx.running, 0);
+	init_completion(&ptl->tx.thread_cplt_pkt);
+	init_completion(&ptl->tx.thread_cplt_tx);
+	init_waitqueue_head(&ptl->tx.packet_wq);
+
+	ptl->rx.thread = NULL;
+	init_waitqueue_head(&ptl->rx.wq);
+
+	spin_lock_init(&ptl->rtx_timeout.lock);
+	ptl->rtx_timeout.timeout = SSH_PTL_PACKET_TIMEOUT;
+	ptl->rtx_timeout.expires = KTIME_MAX;
+	INIT_DELAYED_WORK(&ptl->rtx_timeout.reaper, ssh_ptl_timeout_reap);
+
+	ptl->ops = *ops;
+
+	/* Initialize list of recent/blocked SEQs with invalid sequence IDs. */
+	for (i = 0; i < ARRAY_SIZE(ptl->rx.blocked.seqs); i++)
+		ptl->rx.blocked.seqs[i] = U16_MAX;
+	ptl->rx.blocked.offset = 0;
+
+	status = kfifo_alloc(&ptl->rx.fifo, SSH_PTL_RX_FIFO_LEN, GFP_KERNEL);
+	if (status)
+		return status;
+
+	status = sshp_buf_alloc(&ptl->rx.buf, SSH_PTL_RX_BUF_LEN, GFP_KERNEL);
+	if (status)
+		kfifo_free(&ptl->rx.fifo);
+
+	return status;
+}
+
+/**
+ * ssh_ptl_destroy() - Deinitialize packet transport layer.
+ * @ptl: The packet transport layer to deinitialize.
+ *
+ * Deinitializes the given packet transport layer and frees resources
+ * associated with it. If receiver and/or transmitter threads have been
+ * started, the layer must first be shut down via ssh_ptl_shutdown() before
+ * this function can be called.
+ */
+void ssh_ptl_destroy(struct ssh_ptl *ptl)
+{
+	kfifo_free(&ptl->rx.fifo);
+	sshp_buf_free(&ptl->rx.buf);
+}
diff --git a/drivers/platform/surface/aggregator/ssh_packet_layer.h b/drivers/platform/surface/aggregator/ssh_packet_layer.h
new file mode 100644
index 000000000..64633522f
--- /dev/null
+++ b/drivers/platform/surface/aggregator/ssh_packet_layer.h
@@ -0,0 +1,190 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * SSH packet transport layer.
+ *
+ * Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#ifndef _SURFACE_AGGREGATOR_SSH_PACKET_LAYER_H
+#define _SURFACE_AGGREGATOR_SSH_PACKET_LAYER_H
+
+#include <linux/atomic.h>
+#include <linux/kfifo.h>
+#include <linux/ktime.h>
+#include <linux/list.h>
+#include <linux/serdev.h>
+#include <linux/spinlock.h>
+#include <linux/types.h>
+#include <linux/wait.h>
+#include <linux/workqueue.h>
+
+#include <linux/surface_aggregator/serial_hub.h>
+#include "ssh_parser.h"
+
+/**
+ * enum ssh_ptl_state_flags - State-flags for &struct ssh_ptl.
+ *
+ * @SSH_PTL_SF_SHUTDOWN_BIT:
+ *	Indicates that the packet transport layer has been shut down or is
+ *	being shut down and should not accept any new packets/data.
+ */
+enum ssh_ptl_state_flags {
+	SSH_PTL_SF_SHUTDOWN_BIT,
+};
+
+/**
+ * struct ssh_ptl_ops - Callback operations for packet transport layer.
+ * @data_received: Function called when a data-packet has been received. Both,
+ *                 the packet layer on which the packet has been received and
+ *                 the packet's payload data are provided to this function.
+ */
+struct ssh_ptl_ops {
+	void (*data_received)(struct ssh_ptl *p, const struct ssam_span *data);
+};
+
+/**
+ * struct ssh_ptl - SSH packet transport layer.
+ * @serdev:        Serial device providing the underlying data transport.
+ * @state:         State(-flags) of the transport layer.
+ * @queue:         Packet submission queue.
+ * @queue.lock:    Lock for modifying the packet submission queue.
+ * @queue.head:    List-head of the packet submission queue.
+ * @pending:       Set/list of pending packets.
+ * @pending.lock:  Lock for modifying the pending set.
+ * @pending.head:  List-head of the pending set/list.
+ * @pending.count: Number of currently pending packets.
+ * @tx:            Transmitter subsystem.
+ * @tx.running:    Flag indicating (desired) transmitter thread state.
+ * @tx.thread:     Transmitter thread.
+ * @tx.thread_cplt_tx:  Completion for transmitter thread waiting on transfer.
+ * @tx.thread_cplt_pkt: Completion for transmitter thread waiting on packets.
+ * @tx.packet_wq:  Waitqueue-head for packet transmit completion.
+ * @rx:            Receiver subsystem.
+ * @rx.thread:     Receiver thread.
+ * @rx.wq:         Waitqueue-head for receiver thread.
+ * @rx.fifo:       Buffer for receiving data/pushing data to receiver thread.
+ * @rx.buf:        Buffer for evaluating data on receiver thread.
+ * @rx.blocked:    List of recent/blocked sequence IDs to detect retransmission.
+ * @rx.blocked.seqs:   Array of blocked sequence IDs.
+ * @rx.blocked.offset: Offset indicating where a new ID should be inserted.
+ * @rtx_timeout:   Retransmission timeout subsystem.
+ * @rtx_timeout.lock:    Lock for modifying the retransmission timeout reaper.
+ * @rtx_timeout.timeout: Timeout interval for retransmission.
+ * @rtx_timeout.expires: Time specifying when the reaper work is next scheduled.
+ * @rtx_timeout.reaper:  Work performing timeout checks and subsequent actions.
+ * @ops:           Packet layer operations.
+ */
+struct ssh_ptl {
+	struct serdev_device *serdev;
+	unsigned long state;
+
+	struct {
+		spinlock_t lock;
+		struct list_head head;
+	} queue;
+
+	struct {
+		spinlock_t lock;
+		struct list_head head;
+		atomic_t count;
+	} pending;
+
+	struct {
+		atomic_t running;
+		struct task_struct *thread;
+		struct completion thread_cplt_tx;
+		struct completion thread_cplt_pkt;
+		struct wait_queue_head packet_wq;
+	} tx;
+
+	struct {
+		struct task_struct *thread;
+		struct wait_queue_head wq;
+		struct kfifo fifo;
+		struct sshp_buf buf;
+
+		struct {
+			u16 seqs[8];
+			u16 offset;
+		} blocked;
+	} rx;
+
+	struct {
+		spinlock_t lock;
+		ktime_t timeout;
+		ktime_t expires;
+		struct delayed_work reaper;
+	} rtx_timeout;
+
+	struct ssh_ptl_ops ops;
+};
+
+#define __ssam_prcond(func, p, fmt, ...)		\
+	do {						\
+		typeof(p) __p = (p);			\
+							\
+		if (__p)				\
+			func(__p, fmt, ##__VA_ARGS__);	\
+	} while (0)
+
+#define ptl_dbg(p, fmt, ...)  dev_dbg(&(p)->serdev->dev, fmt, ##__VA_ARGS__)
+#define ptl_info(p, fmt, ...) dev_info(&(p)->serdev->dev, fmt, ##__VA_ARGS__)
+#define ptl_warn(p, fmt, ...) dev_warn(&(p)->serdev->dev, fmt, ##__VA_ARGS__)
+#define ptl_err(p, fmt, ...)  dev_err(&(p)->serdev->dev, fmt, ##__VA_ARGS__)
+#define ptl_dbg_cond(p, fmt, ...) __ssam_prcond(ptl_dbg, p, fmt, ##__VA_ARGS__)
+
+#define to_ssh_ptl(ptr, member) \
+	container_of(ptr, struct ssh_ptl, member)
+
+int ssh_ptl_init(struct ssh_ptl *ptl, struct serdev_device *serdev,
+		 struct ssh_ptl_ops *ops);
+
+void ssh_ptl_destroy(struct ssh_ptl *ptl);
+
+/**
+ * ssh_ptl_get_device() - Get device associated with packet transport layer.
+ * @ptl: The packet transport layer.
+ *
+ * Return: Returns the device on which the given packet transport layer builds
+ * upon.
+ */
+static inline struct device *ssh_ptl_get_device(struct ssh_ptl *ptl)
+{
+	return ptl->serdev ? &ptl->serdev->dev : NULL;
+}
+
+int ssh_ptl_tx_start(struct ssh_ptl *ptl);
+int ssh_ptl_tx_stop(struct ssh_ptl *ptl);
+int ssh_ptl_rx_start(struct ssh_ptl *ptl);
+int ssh_ptl_rx_stop(struct ssh_ptl *ptl);
+void ssh_ptl_shutdown(struct ssh_ptl *ptl);
+
+int ssh_ptl_submit(struct ssh_ptl *ptl, struct ssh_packet *p);
+void ssh_ptl_cancel(struct ssh_packet *p);
+
+int ssh_ptl_rx_rcvbuf(struct ssh_ptl *ptl, const u8 *buf, size_t n);
+
+/**
+ * ssh_ptl_tx_wakeup_transfer() - Wake up packet transmitter thread for
+ * transfer.
+ * @ptl: The packet transport layer.
+ *
+ * Wakes up the packet transmitter thread, notifying it that the underlying
+ * transport has more space for data to be transmitted. If the packet
+ * transport layer has been shut down, calls to this function will be ignored.
+ */
+static inline void ssh_ptl_tx_wakeup_transfer(struct ssh_ptl *ptl)
+{
+	if (test_bit(SSH_PTL_SF_SHUTDOWN_BIT, &ptl->state))
+		return;
+
+	complete(&ptl->tx.thread_cplt_tx);
+}
+
+void ssh_packet_init(struct ssh_packet *packet, unsigned long type,
+		     u8 priority, const struct ssh_packet_ops *ops);
+
+int ssh_ctrl_packet_cache_init(void);
+void ssh_ctrl_packet_cache_destroy(void);
+
+#endif /* _SURFACE_AGGREGATOR_SSH_PACKET_LAYER_H */
diff --git a/drivers/platform/surface/aggregator/ssh_parser.c b/drivers/platform/surface/aggregator/ssh_parser.c
new file mode 100644
index 000000000..a6f668694
--- /dev/null
+++ b/drivers/platform/surface/aggregator/ssh_parser.c
@@ -0,0 +1,228 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * SSH message parser.
+ *
+ * Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#include <asm/unaligned.h>
+#include <linux/compiler.h>
+#include <linux/device.h>
+#include <linux/types.h>
+
+#include <linux/surface_aggregator/serial_hub.h>
+#include "ssh_parser.h"
+
+/**
+ * sshp_validate_crc() - Validate a CRC in raw message data.
+ * @src: The span of data over which the CRC should be computed.
+ * @crc: The pointer to the expected u16 CRC value.
+ *
+ * Computes the CRC of the provided data span (@src), compares it to the CRC
+ * stored at the given address (@crc), and returns the result of this
+ * comparison, i.e. %true if equal. This function is intended to run on raw
+ * input/message data.
+ *
+ * Return: Returns %true if the computed CRC matches the stored CRC, %false
+ * otherwise.
+ */
+static bool sshp_validate_crc(const struct ssam_span *src, const u8 *crc)
+{
+	u16 actual = ssh_crc(src->ptr, src->len);
+	u16 expected = get_unaligned_le16(crc);
+
+	return actual == expected;
+}
+
+/**
+ * sshp_starts_with_syn() - Check if the given data starts with SSH SYN bytes.
+ * @src: The data span to check the start of.
+ */
+static bool sshp_starts_with_syn(const struct ssam_span *src)
+{
+	return src->len >= 2 && get_unaligned_le16(src->ptr) == SSH_MSG_SYN;
+}
+
+/**
+ * sshp_find_syn() - Find SSH SYN bytes in the given data span.
+ * @src: The data span to search in.
+ * @rem: The span (output) indicating the remaining data, starting with SSH
+ *       SYN bytes, if found.
+ *
+ * Search for SSH SYN bytes in the given source span. If found, set the @rem
+ * span to the remaining data, starting with the first SYN bytes and capped by
+ * the source span length, and return %true. This function does not copy any
+ * data, but rather only sets pointers to the respective start addresses and
+ * length values.
+ *
+ * If no SSH SYN bytes could be found, set the @rem span to the zero-length
+ * span at the end of the source span and return %false.
+ *
+ * If partial SSH SYN bytes could be found at the end of the source span, set
+ * the @rem span to cover these partial SYN bytes, capped by the end of the
+ * source span, and return %false. This function should then be re-run once
+ * more data is available.
+ *
+ * Return: Returns %true if a complete SSH SYN sequence could be found,
+ * %false otherwise.
+ */
+bool sshp_find_syn(const struct ssam_span *src, struct ssam_span *rem)
+{
+	size_t i;
+
+	for (i = 0; i < src->len - 1; i++) {
+		if (likely(get_unaligned_le16(src->ptr + i) == SSH_MSG_SYN)) {
+			rem->ptr = src->ptr + i;
+			rem->len = src->len - i;
+			return true;
+		}
+	}
+
+	if (unlikely(src->ptr[src->len - 1] == (SSH_MSG_SYN & 0xff))) {
+		rem->ptr = src->ptr + src->len - 1;
+		rem->len = 1;
+		return false;
+	}
+
+	rem->ptr = src->ptr + src->len;
+	rem->len = 0;
+	return false;
+}
+
+/**
+ * sshp_parse_frame() - Parse SSH frame.
+ * @dev: The device used for logging.
+ * @source: The source to parse from.
+ * @frame: The parsed frame (output).
+ * @payload: The parsed payload (output).
+ * @maxlen: The maximum supported message length.
+ *
+ * Parses and validates a SSH frame, including its payload, from the given
+ * source. Sets the provided @frame pointer to the start of the frame and
+ * writes the limits of the frame payload to the provided @payload span
+ * pointer.
+ *
+ * This function does not copy any data, but rather only validates the message
+ * data and sets pointers (and length values) to indicate the respective parts.
+ *
+ * If no complete SSH frame could be found, the frame pointer will be set to
+ * the %NULL pointer and the payload span will be set to the null span (start
+ * pointer %NULL, size zero).
+ *
+ * Return: Returns zero on success or if the frame is incomplete, %-ENOMSG if
+ * the start of the message is invalid, %-EBADMSG if any (frame-header or
+ * payload) CRC is invalid, or %-EMSGSIZE if the SSH message is bigger than
+ * the maximum message length specified in the @maxlen parameter.
+ */
+int sshp_parse_frame(const struct device *dev, const struct ssam_span *source,
+		     struct ssh_frame **frame, struct ssam_span *payload,
+		     size_t maxlen)
+{
+	struct ssam_span sf;
+	struct ssam_span sp;
+
+	/* Initialize output. */
+	*frame = NULL;
+	payload->ptr = NULL;
+	payload->len = 0;
+
+	if (!sshp_starts_with_syn(source)) {
+		dev_warn(dev, "rx: parser: invalid start of frame\n");
+		return -ENOMSG;
+	}
+
+	/* Check for minimum packet length. */
+	if (unlikely(source->len < SSH_MESSAGE_LENGTH(0))) {
+		dev_dbg(dev, "rx: parser: not enough data for frame\n");
+		return 0;
+	}
+
+	/* Pin down frame. */
+	sf.ptr = source->ptr + sizeof(u16);
+	sf.len = sizeof(struct ssh_frame);
+
+	/* Validate frame CRC. */
+	if (unlikely(!sshp_validate_crc(&sf, sf.ptr + sf.len))) {
+		dev_warn(dev, "rx: parser: invalid frame CRC\n");
+		return -EBADMSG;
+	}
+
+	/* Ensure packet does not exceed maximum length. */
+	sp.len = get_unaligned_le16(&((struct ssh_frame *)sf.ptr)->len);
+	if (unlikely(SSH_MESSAGE_LENGTH(sp.len) > maxlen)) {
+		dev_warn(dev, "rx: parser: frame too large: %llu bytes\n",
+			 SSH_MESSAGE_LENGTH(sp.len));
+		return -EMSGSIZE;
+	}
+
+	/* Pin down payload. */
+	sp.ptr = sf.ptr + sf.len + sizeof(u16);
+
+	/* Check for frame + payload length. */
+	if (source->len < SSH_MESSAGE_LENGTH(sp.len)) {
+		dev_dbg(dev, "rx: parser: not enough data for payload\n");
+		return 0;
+	}
+
+	/* Validate payload CRC. */
+	if (unlikely(!sshp_validate_crc(&sp, sp.ptr + sp.len))) {
+		dev_warn(dev, "rx: parser: invalid payload CRC\n");
+		return -EBADMSG;
+	}
+
+	*frame = (struct ssh_frame *)sf.ptr;
+	*payload = sp;
+
+	dev_dbg(dev, "rx: parser: valid frame found (type: %#04x, len: %u)\n",
+		(*frame)->type, (*frame)->len);
+
+	return 0;
+}
+
+/**
+ * sshp_parse_command() - Parse SSH command frame payload.
+ * @dev: The device used for logging.
+ * @source: The source to parse from.
+ * @command: The parsed command (output).
+ * @command_data: The parsed command data/payload (output).
+ *
+ * Parses and validates a SSH command frame payload. Sets the @command pointer
+ * to the command header and the @command_data span to the command data (i.e.
+ * payload of the command). This will result in a zero-length span if the
+ * command does not have any associated data/payload. This function does not
+ * check the frame-payload-type field, which should be checked by the caller
+ * before calling this function.
+ *
+ * The @source parameter should be the complete frame payload, e.g. returned
+ * by the sshp_parse_frame() command.
+ *
+ * This function does not copy any data, but rather only validates the frame
+ * payload data and sets pointers (and length values) to indicate the
+ * respective parts.
+ *
+ * Return: Returns zero on success or %-ENOMSG if @source does not represent a
+ * valid command-type frame payload, i.e. is too short.
+ */
+int sshp_parse_command(const struct device *dev, const struct ssam_span *source,
+		       struct ssh_command **command,
+		       struct ssam_span *command_data)
+{
+	/* Check for minimum length. */
+	if (unlikely(source->len < sizeof(struct ssh_command))) {
+		*command = NULL;
+		command_data->ptr = NULL;
+		command_data->len = 0;
+
+		dev_err(dev, "rx: parser: command payload is too short\n");
+		return -ENOMSG;
+	}
+
+	*command = (struct ssh_command *)source->ptr;
+	command_data->ptr = source->ptr + sizeof(struct ssh_command);
+	command_data->len = source->len - sizeof(struct ssh_command);
+
+	dev_dbg(dev, "rx: parser: valid command found (tc: %#04x, cid: %#04x)\n",
+		(*command)->tc, (*command)->cid);
+
+	return 0;
+}
diff --git a/drivers/platform/surface/aggregator/ssh_parser.h b/drivers/platform/surface/aggregator/ssh_parser.h
new file mode 100644
index 000000000..801d8fa69
--- /dev/null
+++ b/drivers/platform/surface/aggregator/ssh_parser.h
@@ -0,0 +1,154 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * SSH message parser.
+ *
+ * Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#ifndef _SURFACE_AGGREGATOR_SSH_PARSER_H
+#define _SURFACE_AGGREGATOR_SSH_PARSER_H
+
+#include <linux/device.h>
+#include <linux/kfifo.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+
+#include <linux/surface_aggregator/serial_hub.h>
+
+/**
+ * struct sshp_buf - Parser buffer for SSH messages.
+ * @ptr: Pointer to the beginning of the buffer.
+ * @len: Number of bytes used in the buffer.
+ * @cap: Maximum capacity of the buffer.
+ */
+struct sshp_buf {
+	u8    *ptr;
+	size_t len;
+	size_t cap;
+};
+
+/**
+ * sshp_buf_init() - Initialize a SSH parser buffer.
+ * @buf: The buffer to initialize.
+ * @ptr: The memory backing the buffer.
+ * @cap: The length of the memory backing the buffer, i.e. its capacity.
+ *
+ * Initializes the buffer with the given memory as backing and set its used
+ * length to zero.
+ */
+static inline void sshp_buf_init(struct sshp_buf *buf, u8 *ptr, size_t cap)
+{
+	buf->ptr = ptr;
+	buf->len = 0;
+	buf->cap = cap;
+}
+
+/**
+ * sshp_buf_alloc() - Allocate and initialize a SSH parser buffer.
+ * @buf:   The buffer to initialize/allocate to.
+ * @cap:   The desired capacity of the buffer.
+ * @flags: The flags used for allocating the memory.
+ *
+ * Allocates @cap bytes and initializes the provided buffer struct with the
+ * allocated memory.
+ *
+ * Return: Returns zero on success and %-ENOMEM if allocation failed.
+ */
+static inline int sshp_buf_alloc(struct sshp_buf *buf, size_t cap, gfp_t flags)
+{
+	u8 *ptr;
+
+	ptr = kzalloc(cap, flags);
+	if (!ptr)
+		return -ENOMEM;
+
+	sshp_buf_init(buf, ptr, cap);
+	return 0;
+}
+
+/**
+ * sshp_buf_free() - Free a SSH parser buffer.
+ * @buf: The buffer to free.
+ *
+ * Frees a SSH parser buffer by freeing the memory backing it and then
+ * resetting its pointer to %NULL and length and capacity to zero. Intended to
+ * free a buffer previously allocated with sshp_buf_alloc().
+ */
+static inline void sshp_buf_free(struct sshp_buf *buf)
+{
+	kfree(buf->ptr);
+	buf->ptr = NULL;
+	buf->len = 0;
+	buf->cap = 0;
+}
+
+/**
+ * sshp_buf_drop() - Drop data from the beginning of the buffer.
+ * @buf: The buffer to drop data from.
+ * @n:   The number of bytes to drop.
+ *
+ * Drops the first @n bytes from the buffer. Re-aligns any remaining data to
+ * the beginning of the buffer.
+ */
+static inline void sshp_buf_drop(struct sshp_buf *buf, size_t n)
+{
+	memmove(buf->ptr, buf->ptr + n, buf->len - n);
+	buf->len -= n;
+}
+
+/**
+ * sshp_buf_read_from_fifo() - Transfer data from a fifo to the buffer.
+ * @buf:  The buffer to write the data into.
+ * @fifo: The fifo to read the data from.
+ *
+ * Transfers the data contained in the fifo to the buffer, removing it from
+ * the fifo. This function will try to transfer as much data as possible,
+ * limited either by the remaining space in the buffer or by the number of
+ * bytes available in the fifo.
+ *
+ * Return: Returns the number of bytes transferred.
+ */
+static inline size_t sshp_buf_read_from_fifo(struct sshp_buf *buf,
+					     struct kfifo *fifo)
+{
+	size_t n;
+
+	n =  kfifo_out(fifo, buf->ptr + buf->len, buf->cap - buf->len);
+	buf->len += n;
+
+	return n;
+}
+
+/**
+ * sshp_buf_span_from() - Initialize a span from the given buffer and offset.
+ * @buf:    The buffer to create the span from.
+ * @offset: The offset in the buffer at which the span should start.
+ * @span:   The span to initialize (output).
+ *
+ * Initializes the provided span to point to the memory at the given offset in
+ * the buffer, with the length of the span being capped by the number of bytes
+ * used in the buffer after the offset (i.e. bytes remaining after the
+ * offset).
+ *
+ * Warning: This function does not validate that @offset is less than or equal
+ * to the number of bytes used in the buffer or the buffer capacity. This must
+ * be guaranteed by the caller.
+ */
+static inline void sshp_buf_span_from(struct sshp_buf *buf, size_t offset,
+				      struct ssam_span *span)
+{
+	span->ptr = buf->ptr + offset;
+	span->len = buf->len - offset;
+}
+
+bool sshp_find_syn(const struct ssam_span *src, struct ssam_span *rem);
+
+int sshp_parse_frame(const struct device *dev, const struct ssam_span *source,
+		     struct ssh_frame **frame, struct ssam_span *payload,
+		     size_t maxlen);
+
+int sshp_parse_command(const struct device *dev, const struct ssam_span *source,
+		       struct ssh_command **command,
+		       struct ssam_span *command_data);
+
+#endif /* _SURFACE_AGGREGATOR_SSH_PARSER_h */
diff --git a/drivers/platform/surface/aggregator/ssh_request_layer.c b/drivers/platform/surface/aggregator/ssh_request_layer.c
new file mode 100644
index 000000000..69132976d
--- /dev/null
+++ b/drivers/platform/surface/aggregator/ssh_request_layer.c
@@ -0,0 +1,1273 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * SSH request transport layer.
+ *
+ * Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#include <asm/unaligned.h>
+#include <linux/atomic.h>
+#include <linux/completion.h>
+#include <linux/error-injection.h>
+#include <linux/ktime.h>
+#include <linux/limits.h>
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/types.h>
+#include <linux/workqueue.h>
+
+#include <linux/surface_aggregator/serial_hub.h>
+#include <linux/surface_aggregator/controller.h>
+
+#include "ssh_packet_layer.h"
+#include "ssh_request_layer.h"
+
+#include "trace.h"
+
+/*
+ * SSH_RTL_REQUEST_TIMEOUT - Request timeout.
+ *
+ * Timeout as ktime_t delta for request responses. If we have not received a
+ * response in this time-frame after finishing the underlying packet
+ * transmission, the request will be completed with %-ETIMEDOUT as status
+ * code.
+ */
+#define SSH_RTL_REQUEST_TIMEOUT			ms_to_ktime(3000)
+
+/*
+ * SSH_RTL_REQUEST_TIMEOUT_RESOLUTION - Request timeout granularity.
+ *
+ * Time-resolution for timeouts. Should be larger than one jiffy to avoid
+ * direct re-scheduling of reaper work_struct.
+ */
+#define SSH_RTL_REQUEST_TIMEOUT_RESOLUTION	ms_to_ktime(max(2000 / HZ, 50))
+
+/*
+ * SSH_RTL_MAX_PENDING - Maximum number of pending requests.
+ *
+ * Maximum number of requests concurrently waiting to be completed (i.e.
+ * waiting for the corresponding packet transmission to finish if they don't
+ * have a response or waiting for a response if they have one).
+ */
+#define SSH_RTL_MAX_PENDING		3
+
+/*
+ * SSH_RTL_TX_BATCH - Maximum number of requests processed per work execution.
+ * Used to prevent livelocking of the workqueue. Value chosen via educated
+ * guess, may be adjusted.
+ */
+#define SSH_RTL_TX_BATCH		10
+
+#ifdef CONFIG_SURFACE_AGGREGATOR_ERROR_INJECTION
+
+/**
+ * ssh_rtl_should_drop_response() - Error injection hook to drop request
+ * responses.
+ *
+ * Useful to cause request transmission timeouts in the driver by dropping the
+ * response to a request.
+ */
+static noinline bool ssh_rtl_should_drop_response(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_rtl_should_drop_response, TRUE);
+
+#else
+
+static inline bool ssh_rtl_should_drop_response(void)
+{
+	return false;
+}
+
+#endif
+
+static u16 ssh_request_get_rqid(struct ssh_request *rqst)
+{
+	return get_unaligned_le16(rqst->packet.data.ptr
+				  + SSH_MSGOFFSET_COMMAND(rqid));
+}
+
+static u32 ssh_request_get_rqid_safe(struct ssh_request *rqst)
+{
+	if (!rqst->packet.data.ptr)
+		return U32_MAX;
+
+	return ssh_request_get_rqid(rqst);
+}
+
+static void ssh_rtl_queue_remove(struct ssh_request *rqst)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+
+	spin_lock(&rtl->queue.lock);
+
+	if (!test_and_clear_bit(SSH_REQUEST_SF_QUEUED_BIT, &rqst->state)) {
+		spin_unlock(&rtl->queue.lock);
+		return;
+	}
+
+	list_del(&rqst->node);
+
+	spin_unlock(&rtl->queue.lock);
+	ssh_request_put(rqst);
+}
+
+static bool ssh_rtl_queue_empty(struct ssh_rtl *rtl)
+{
+	bool empty;
+
+	spin_lock(&rtl->queue.lock);
+	empty = list_empty(&rtl->queue.head);
+	spin_unlock(&rtl->queue.lock);
+
+	return empty;
+}
+
+static void ssh_rtl_pending_remove(struct ssh_request *rqst)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+
+	spin_lock(&rtl->pending.lock);
+
+	if (!test_and_clear_bit(SSH_REQUEST_SF_PENDING_BIT, &rqst->state)) {
+		spin_unlock(&rtl->pending.lock);
+		return;
+	}
+
+	atomic_dec(&rtl->pending.count);
+	list_del(&rqst->node);
+
+	spin_unlock(&rtl->pending.lock);
+
+	ssh_request_put(rqst);
+}
+
+static int ssh_rtl_tx_pending_push(struct ssh_request *rqst)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+
+	spin_lock(&rtl->pending.lock);
+
+	if (test_bit(SSH_REQUEST_SF_LOCKED_BIT, &rqst->state)) {
+		spin_unlock(&rtl->pending.lock);
+		return -EINVAL;
+	}
+
+	if (test_and_set_bit(SSH_REQUEST_SF_PENDING_BIT, &rqst->state)) {
+		spin_unlock(&rtl->pending.lock);
+		return -EALREADY;
+	}
+
+	atomic_inc(&rtl->pending.count);
+	list_add_tail(&ssh_request_get(rqst)->node, &rtl->pending.head);
+
+	spin_unlock(&rtl->pending.lock);
+	return 0;
+}
+
+static void ssh_rtl_complete_with_status(struct ssh_request *rqst, int status)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+
+	trace_ssam_request_complete(rqst, status);
+
+	/* rtl/ptl may not be set if we're canceling before submitting. */
+	rtl_dbg_cond(rtl, "rtl: completing request (rqid: %#06x, status: %d)\n",
+		     ssh_request_get_rqid_safe(rqst), status);
+
+	rqst->ops->complete(rqst, NULL, NULL, status);
+}
+
+static void ssh_rtl_complete_with_rsp(struct ssh_request *rqst,
+				      const struct ssh_command *cmd,
+				      const struct ssam_span *data)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+
+	trace_ssam_request_complete(rqst, 0);
+
+	rtl_dbg(rtl, "rtl: completing request with response (rqid: %#06x)\n",
+		ssh_request_get_rqid(rqst));
+
+	rqst->ops->complete(rqst, cmd, data, 0);
+}
+
+static bool ssh_rtl_tx_can_process(struct ssh_request *rqst)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+
+	if (test_bit(SSH_REQUEST_TY_FLUSH_BIT, &rqst->state))
+		return !atomic_read(&rtl->pending.count);
+
+	return atomic_read(&rtl->pending.count) < SSH_RTL_MAX_PENDING;
+}
+
+static struct ssh_request *ssh_rtl_tx_next(struct ssh_rtl *rtl)
+{
+	struct ssh_request *rqst = ERR_PTR(-ENOENT);
+	struct ssh_request *p, *n;
+
+	spin_lock(&rtl->queue.lock);
+
+	/* Find first non-locked request and remove it. */
+	list_for_each_entry_safe(p, n, &rtl->queue.head, node) {
+		if (unlikely(test_bit(SSH_REQUEST_SF_LOCKED_BIT, &p->state)))
+			continue;
+
+		if (!ssh_rtl_tx_can_process(p)) {
+			rqst = ERR_PTR(-EBUSY);
+			break;
+		}
+
+		/* Remove from queue and mark as transmitting. */
+		set_bit(SSH_REQUEST_SF_TRANSMITTING_BIT, &p->state);
+		/* Ensure state never gets zero. */
+		smp_mb__before_atomic();
+		clear_bit(SSH_REQUEST_SF_QUEUED_BIT, &p->state);
+
+		list_del(&p->node);
+
+		rqst = p;
+		break;
+	}
+
+	spin_unlock(&rtl->queue.lock);
+	return rqst;
+}
+
+static int ssh_rtl_tx_try_process_one(struct ssh_rtl *rtl)
+{
+	struct ssh_request *rqst;
+	int status;
+
+	/* Get and prepare next request for transmit. */
+	rqst = ssh_rtl_tx_next(rtl);
+	if (IS_ERR(rqst))
+		return PTR_ERR(rqst);
+
+	/* Add it to/mark it as pending. */
+	status = ssh_rtl_tx_pending_push(rqst);
+	if (status) {
+		ssh_request_put(rqst);
+		return -EAGAIN;
+	}
+
+	/* Submit packet. */
+	status = ssh_ptl_submit(&rtl->ptl, &rqst->packet);
+	if (status == -ESHUTDOWN) {
+		/*
+		 * Packet has been refused due to the packet layer shutting
+		 * down. Complete it here.
+		 */
+		set_bit(SSH_REQUEST_SF_LOCKED_BIT, &rqst->state);
+		/*
+		 * Note: A barrier is not required here, as there are only two
+		 * references in the system at this point: The one that we have,
+		 * and the other one that belongs to the pending set. Due to the
+		 * request being marked as "transmitting", our process is the
+		 * only one allowed to remove the pending node and change the
+		 * state. Normally, the task would fall to the packet callback,
+		 * but as this is a path where submission failed, this callback
+		 * will never be executed.
+		 */
+
+		ssh_rtl_pending_remove(rqst);
+		ssh_rtl_complete_with_status(rqst, -ESHUTDOWN);
+
+		ssh_request_put(rqst);
+		return -ESHUTDOWN;
+
+	} else if (status) {
+		/*
+		 * If submitting the packet failed and the packet layer isn't
+		 * shutting down, the packet has either been submitted/queued
+		 * before (-EALREADY, which cannot happen as we have
+		 * guaranteed that requests cannot be re-submitted), or the
+		 * packet was marked as locked (-EINVAL). To mark the packet
+		 * locked at this stage, the request, and thus the packets
+		 * itself, had to have been canceled. Simply drop the
+		 * reference. Cancellation itself will remove it from the set
+		 * of pending requests.
+		 */
+
+		WARN_ON(status != -EINVAL);
+
+		ssh_request_put(rqst);
+		return -EAGAIN;
+	}
+
+	ssh_request_put(rqst);
+	return 0;
+}
+
+static bool ssh_rtl_tx_schedule(struct ssh_rtl *rtl)
+{
+	if (atomic_read(&rtl->pending.count) >= SSH_RTL_MAX_PENDING)
+		return false;
+
+	if (ssh_rtl_queue_empty(rtl))
+		return false;
+
+	return schedule_work(&rtl->tx.work);
+}
+
+static void ssh_rtl_tx_work_fn(struct work_struct *work)
+{
+	struct ssh_rtl *rtl = to_ssh_rtl(work, tx.work);
+	unsigned int iterations = SSH_RTL_TX_BATCH;
+	int status;
+
+	/*
+	 * Try to be nice and not block/live-lock the workqueue: Run a maximum
+	 * of 10 tries, then re-submit if necessary. This should not be
+	 * necessary for normal execution, but guarantee it anyway.
+	 */
+	do {
+		status = ssh_rtl_tx_try_process_one(rtl);
+		if (status == -ENOENT || status == -EBUSY)
+			return;		/* No more requests to process. */
+
+		if (status == -ESHUTDOWN) {
+			/*
+			 * Packet system shutting down. No new packets can be
+			 * transmitted. Return silently, the party initiating
+			 * the shutdown should handle the rest.
+			 */
+			return;
+		}
+
+		WARN_ON(status != 0 && status != -EAGAIN);
+	} while (--iterations);
+
+	/* Out of tries, reschedule. */
+	ssh_rtl_tx_schedule(rtl);
+}
+
+/**
+ * ssh_rtl_submit() - Submit a request to the transport layer.
+ * @rtl:  The request transport layer.
+ * @rqst: The request to submit.
+ *
+ * Submits a request to the transport layer. A single request may not be
+ * submitted multiple times without reinitializing it.
+ *
+ * Return: Returns zero on success, %-EINVAL if the request type is invalid or
+ * the request has been canceled prior to submission, %-EALREADY if the
+ * request has already been submitted, or %-ESHUTDOWN in case the request
+ * transport layer has been shut down.
+ */
+int ssh_rtl_submit(struct ssh_rtl *rtl, struct ssh_request *rqst)
+{
+	trace_ssam_request_submit(rqst);
+
+	/*
+	 * Ensure that requests expecting a response are sequenced. If this
+	 * invariant ever changes, see the comment in ssh_rtl_complete() on what
+	 * is required to be changed in the code.
+	 */
+	if (test_bit(SSH_REQUEST_TY_HAS_RESPONSE_BIT, &rqst->state))
+		if (!test_bit(SSH_PACKET_TY_SEQUENCED_BIT, &rqst->packet.state))
+			return -EINVAL;
+
+	spin_lock(&rtl->queue.lock);
+
+	/*
+	 * Try to set ptl and check if this request has already been submitted.
+	 *
+	 * Must be inside lock as we might run into a lost update problem
+	 * otherwise: If this were outside of the lock, cancellation in
+	 * ssh_rtl_cancel_nonpending() may run after we've set the ptl
+	 * reference but before we enter the lock. In that case, we'd detect
+	 * that the request is being added to the queue and would try to remove
+	 * it from that, but removal might fail because it hasn't actually been
+	 * added yet. By putting this cmpxchg in the critical section, we
+	 * ensure that the queuing detection only triggers when we are already
+	 * in the critical section and the remove process will wait until the
+	 * push operation has been completed (via lock) due to that. Only then,
+	 * we can safely try to remove it.
+	 */
+	if (cmpxchg(&rqst->packet.ptl, NULL, &rtl->ptl)) {
+		spin_unlock(&rtl->queue.lock);
+		return -EALREADY;
+	}
+
+	/*
+	 * Ensure that we set ptl reference before we continue modifying state.
+	 * This is required for non-pending cancellation. This barrier is paired
+	 * with the one in ssh_rtl_cancel_nonpending().
+	 *
+	 * By setting the ptl reference before we test for "locked", we can
+	 * check if the "locked" test may have already run. See comments in
+	 * ssh_rtl_cancel_nonpending() for more detail.
+	 */
+	smp_mb__after_atomic();
+
+	if (test_bit(SSH_RTL_SF_SHUTDOWN_BIT, &rtl->state)) {
+		spin_unlock(&rtl->queue.lock);
+		return -ESHUTDOWN;
+	}
+
+	if (test_bit(SSH_REQUEST_SF_LOCKED_BIT, &rqst->state)) {
+		spin_unlock(&rtl->queue.lock);
+		return -EINVAL;
+	}
+
+	set_bit(SSH_REQUEST_SF_QUEUED_BIT, &rqst->state);
+	list_add_tail(&ssh_request_get(rqst)->node, &rtl->queue.head);
+
+	spin_unlock(&rtl->queue.lock);
+
+	ssh_rtl_tx_schedule(rtl);
+	return 0;
+}
+
+static void ssh_rtl_timeout_reaper_mod(struct ssh_rtl *rtl, ktime_t now,
+				       ktime_t expires)
+{
+	unsigned long delta = msecs_to_jiffies(ktime_ms_delta(expires, now));
+	ktime_t aexp = ktime_add(expires, SSH_RTL_REQUEST_TIMEOUT_RESOLUTION);
+
+	spin_lock(&rtl->rtx_timeout.lock);
+
+	/* Re-adjust / schedule reaper only if it is above resolution delta. */
+	if (ktime_before(aexp, rtl->rtx_timeout.expires)) {
+		rtl->rtx_timeout.expires = expires;
+		mod_delayed_work(system_wq, &rtl->rtx_timeout.reaper, delta);
+	}
+
+	spin_unlock(&rtl->rtx_timeout.lock);
+}
+
+static void ssh_rtl_timeout_start(struct ssh_request *rqst)
+{
+	struct ssh_rtl *rtl = ssh_request_rtl(rqst);
+	ktime_t timestamp = ktime_get_coarse_boottime();
+	ktime_t timeout = rtl->rtx_timeout.timeout;
+
+	if (test_bit(SSH_REQUEST_SF_LOCKED_BIT, &rqst->state))
+		return;
+
+	/*
+	 * Note: The timestamp gets set only once. This happens on the packet
+	 * callback. All other access to it is read-only.
+	 */
+	WRITE_ONCE(rqst->timestamp, timestamp);
+	/*
+	 * Ensure timestamp is set before starting the reaper. Paired with
+	 * implicit barrier following check on ssh_request_get_expiration() in
+	 * ssh_rtl_timeout_reap.
+	 */
+	smp_mb__after_atomic();
+
+	ssh_rtl_timeout_reaper_mod(rtl, timestamp, timestamp + timeout);
+}
+
+static void ssh_rtl_complete(struct ssh_rtl *rtl,
+			     const struct ssh_command *command,
+			     const struct ssam_span *command_data)
+{
+	struct ssh_request *r = NULL;
+	struct ssh_request *p, *n;
+	u16 rqid = get_unaligned_le16(&command->rqid);
+
+	trace_ssam_rx_response_received(command, command_data->len);
+
+	/*
+	 * Get request from pending based on request ID and mark it as response
+	 * received and locked.
+	 */
+	spin_lock(&rtl->pending.lock);
+	list_for_each_entry_safe(p, n, &rtl->pending.head, node) {
+		/* We generally expect requests to be processed in order. */
+		if (unlikely(ssh_request_get_rqid(p) != rqid))
+			continue;
+
+		/* Simulate response timeout. */
+		if (ssh_rtl_should_drop_response()) {
+			spin_unlock(&rtl->pending.lock);
+
+			trace_ssam_ei_rx_drop_response(p);
+			rtl_info(rtl, "request error injection: dropping response for request %p\n",
+				 &p->packet);
+			return;
+		}
+
+		/*
+		 * Mark as "response received" and "locked" as we're going to
+		 * complete it.
+		 */
+		set_bit(SSH_REQUEST_SF_LOCKED_BIT, &p->state);
+		set_bit(SSH_REQUEST_SF_RSPRCVD_BIT, &p->state);
+		/* Ensure state never gets zero. */
+		smp_mb__before_atomic();
+		clear_bit(SSH_REQUEST_SF_PENDING_BIT, &p->state);
+
+		atomic_dec(&rtl->pending.count);
+		list_del(&p->node);
+
+		r = p;
+		break;
+	}
+	spin_unlock(&rtl->pending.lock);
+
+	if (!r) {
+		rtl_warn(rtl, "rtl: dropping unexpected command message (rqid = %#06x)\n",
+			 rqid);
+		return;
+	}
+
+	/* If the request hasn't been completed yet, we will do this now. */
+	if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state)) {
+		ssh_request_put(r);
+		ssh_rtl_tx_schedule(rtl);
+		return;
+	}
+
+	/*
+	 * Make sure the request has been transmitted. In case of a sequenced
+	 * request, we are guaranteed that the completion callback will run on
+	 * the receiver thread directly when the ACK for the packet has been
+	 * received. Similarly, this function is guaranteed to run on the
+	 * receiver thread. Thus we are guaranteed that if the packet has been
+	 * successfully transmitted and received an ACK, the transmitted flag
+	 * has been set and is visible here.
+	 *
+	 * We are currently not handling unsequenced packets here, as those
+	 * should never expect a response as ensured in ssh_rtl_submit. If this
+	 * ever changes, one would have to test for
+	 *
+	 *	(r->state & (transmitting | transmitted))
+	 *
+	 * on unsequenced packets to determine if they could have been
+	 * transmitted. There are no synchronization guarantees as in the
+	 * sequenced case, since, in this case, the callback function will not
+	 * run on the same thread. Thus an exact determination is impossible.
+	 */
+	if (!test_bit(SSH_REQUEST_SF_TRANSMITTED_BIT, &r->state)) {
+		rtl_err(rtl, "rtl: received response before ACK for request (rqid = %#06x)\n",
+			rqid);
+
+		/*
+		 * NB: Timeout has already been canceled, request already been
+		 * removed from pending and marked as locked and completed. As
+		 * we receive a "false" response, the packet might still be
+		 * queued though.
+		 */
+		ssh_rtl_queue_remove(r);
+
+		ssh_rtl_complete_with_status(r, -EREMOTEIO);
+		ssh_request_put(r);
+
+		ssh_rtl_tx_schedule(rtl);
+		return;
+	}
+
+	/*
+	 * NB: Timeout has already been canceled, request already been
+	 * removed from pending and marked as locked and completed. The request
+	 * can also not be queued any more, as it has been marked as
+	 * transmitting and later transmitted. Thus no need to remove it from
+	 * anywhere.
+	 */
+
+	ssh_rtl_complete_with_rsp(r, command, command_data);
+	ssh_request_put(r);
+
+	ssh_rtl_tx_schedule(rtl);
+}
+
+static bool ssh_rtl_cancel_nonpending(struct ssh_request *r)
+{
+	struct ssh_rtl *rtl;
+	unsigned long flags, fixed;
+	bool remove;
+
+	/*
+	 * Handle unsubmitted request: Try to mark the packet as locked,
+	 * expecting the state to be zero (i.e. unsubmitted). Note that, if
+	 * setting the state worked, we might still be adding the packet to the
+	 * queue in a currently executing submit call. In that case, however,
+	 * ptl reference must have been set previously, as locked is checked
+	 * after setting ptl. Furthermore, when the ptl reference is set, the
+	 * submission process is guaranteed to have entered the critical
+	 * section. Thus only if we successfully locked this request and ptl is
+	 * NULL, we have successfully removed the request, i.e. we are
+	 * guaranteed that, due to the "locked" check in ssh_rtl_submit(), the
+	 * packet will never be added. Otherwise, we need to try and grab it
+	 * from the queue, where we are now guaranteed that the packet is or has
+	 * been due to the critical section.
+	 *
+	 * Note that if the cmpxchg() fails, we are guaranteed that ptl has
+	 * been set and is non-NULL, as states can only be nonzero after this
+	 * has been set. Also note that we need to fetch the static (type)
+	 * flags to ensure that they don't cause the cmpxchg() to fail.
+	 */
+	fixed = READ_ONCE(r->state) & SSH_REQUEST_FLAGS_TY_MASK;
+	flags = cmpxchg(&r->state, fixed, SSH_REQUEST_SF_LOCKED_BIT);
+
+	/*
+	 * Force correct ordering with regards to state and ptl reference access
+	 * to safe-guard cancellation to concurrent submission against a
+	 * lost-update problem. First try to exchange state, then also check
+	 * ptl if that worked. This barrier is paired with the
+	 * one in ssh_rtl_submit().
+	 */
+	smp_mb__after_atomic();
+
+	if (flags == fixed && !READ_ONCE(r->packet.ptl)) {
+		if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+			return true;
+
+		ssh_rtl_complete_with_status(r, -ECANCELED);
+		return true;
+	}
+
+	rtl = ssh_request_rtl(r);
+	spin_lock(&rtl->queue.lock);
+
+	/*
+	 * Note: 1) Requests cannot be re-submitted. 2) If a request is
+	 * queued, it cannot be "transmitting"/"pending" yet. Thus, if we
+	 * successfully remove the request here, we have removed all its
+	 * occurrences in the system.
+	 */
+
+	remove = test_and_clear_bit(SSH_REQUEST_SF_QUEUED_BIT, &r->state);
+	if (!remove) {
+		spin_unlock(&rtl->queue.lock);
+		return false;
+	}
+
+	set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state);
+	list_del(&r->node);
+
+	spin_unlock(&rtl->queue.lock);
+
+	ssh_request_put(r);	/* Drop reference obtained from queue. */
+
+	if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+		return true;
+
+	ssh_rtl_complete_with_status(r, -ECANCELED);
+	return true;
+}
+
+static bool ssh_rtl_cancel_pending(struct ssh_request *r)
+{
+	/* If the packet is already locked, it's going to be removed shortly. */
+	if (test_and_set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state))
+		return true;
+
+	/*
+	 * Now that we have locked the packet, we have guaranteed that it can't
+	 * be added to the system any more. If ptl is NULL, the locked
+	 * check in ssh_rtl_submit() has not been run and any submission,
+	 * currently in progress or called later, won't add the packet. Thus we
+	 * can directly complete it.
+	 *
+	 * The implicit memory barrier of test_and_set_bit() should be enough
+	 * to ensure that the correct order (first lock, then check ptl) is
+	 * ensured. This is paired with the barrier in ssh_rtl_submit().
+	 */
+	if (!READ_ONCE(r->packet.ptl)) {
+		if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+			return true;
+
+		ssh_rtl_complete_with_status(r, -ECANCELED);
+		return true;
+	}
+
+	/*
+	 * Try to cancel the packet. If the packet has not been completed yet,
+	 * this will subsequently (and synchronously) call the completion
+	 * callback of the packet, which will complete the request.
+	 */
+	ssh_ptl_cancel(&r->packet);
+
+	/*
+	 * If the packet has been completed with success, i.e. has not been
+	 * canceled by the above call, the request may not have been completed
+	 * yet (may be waiting for a response). Check if we need to do this
+	 * here.
+	 */
+	if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+		return true;
+
+	ssh_rtl_queue_remove(r);
+	ssh_rtl_pending_remove(r);
+	ssh_rtl_complete_with_status(r, -ECANCELED);
+
+	return true;
+}
+
+/**
+ * ssh_rtl_cancel() - Cancel request.
+ * @rqst:    The request to cancel.
+ * @pending: Whether to also cancel pending requests.
+ *
+ * Cancels the given request. If @pending is %false, this will not cancel
+ * pending requests, i.e. requests that have already been submitted to the
+ * packet layer but not been completed yet. If @pending is %true, this will
+ * cancel the given request regardless of the state it is in.
+ *
+ * If the request has been canceled by calling this function, both completion
+ * and release callbacks of the request will be executed in a reasonable
+ * time-frame. This may happen during execution of this function, however,
+ * there is no guarantee for this. For example, a request currently
+ * transmitting will be canceled/completed only after transmission has
+ * completed, and the respective callbacks will be executed on the transmitter
+ * thread, which may happen during, but also some time after execution of the
+ * cancel function.
+ *
+ * Return: Returns %true if the given request has been canceled or completed,
+ * either by this function or prior to calling this function, %false
+ * otherwise. If @pending is %true, this function will always return %true.
+ */
+bool ssh_rtl_cancel(struct ssh_request *rqst, bool pending)
+{
+	struct ssh_rtl *rtl;
+	bool canceled;
+
+	if (test_and_set_bit(SSH_REQUEST_SF_CANCELED_BIT, &rqst->state))
+		return true;
+
+	trace_ssam_request_cancel(rqst);
+
+	if (pending)
+		canceled = ssh_rtl_cancel_pending(rqst);
+	else
+		canceled = ssh_rtl_cancel_nonpending(rqst);
+
+	/* Note: rtl may be NULL if request has not been submitted yet. */
+	rtl = ssh_request_rtl(rqst);
+	if (canceled && rtl)
+		ssh_rtl_tx_schedule(rtl);
+
+	return canceled;
+}
+
+static void ssh_rtl_packet_callback(struct ssh_packet *p, int status)
+{
+	struct ssh_request *r = to_ssh_request(p);
+
+	if (unlikely(status)) {
+		set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state);
+
+		if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+			return;
+
+		/*
+		 * The packet may get canceled even though it has not been
+		 * submitted yet. The request may still be queued. Check the
+		 * queue and remove it if necessary. As the timeout would have
+		 * been started in this function on success, there's no need
+		 * to cancel it here.
+		 */
+		ssh_rtl_queue_remove(r);
+		ssh_rtl_pending_remove(r);
+		ssh_rtl_complete_with_status(r, status);
+
+		ssh_rtl_tx_schedule(ssh_request_rtl(r));
+		return;
+	}
+
+	/* Update state: Mark as transmitted and clear transmitting. */
+	set_bit(SSH_REQUEST_SF_TRANSMITTED_BIT, &r->state);
+	/* Ensure state never gets zero. */
+	smp_mb__before_atomic();
+	clear_bit(SSH_REQUEST_SF_TRANSMITTING_BIT, &r->state);
+
+	/* If we expect a response, we just need to start the timeout. */
+	if (test_bit(SSH_REQUEST_TY_HAS_RESPONSE_BIT, &r->state)) {
+		/*
+		 * Note: This is the only place where the timestamp gets set,
+		 * all other access to it is read-only.
+		 */
+		ssh_rtl_timeout_start(r);
+		return;
+	}
+
+	/*
+	 * If we don't expect a response, lock, remove, and complete the
+	 * request. Note that, at this point, the request is guaranteed to have
+	 * left the queue and no timeout has been started. Thus we only need to
+	 * remove it from pending. If the request has already been completed (it
+	 * may have been canceled) return.
+	 */
+
+	set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state);
+	if (test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+		return;
+
+	ssh_rtl_pending_remove(r);
+	ssh_rtl_complete_with_status(r, 0);
+
+	ssh_rtl_tx_schedule(ssh_request_rtl(r));
+}
+
+static ktime_t ssh_request_get_expiration(struct ssh_request *r, ktime_t timeout)
+{
+	ktime_t timestamp = READ_ONCE(r->timestamp);
+
+	if (timestamp != KTIME_MAX)
+		return ktime_add(timestamp, timeout);
+	else
+		return KTIME_MAX;
+}
+
+static void ssh_rtl_timeout_reap(struct work_struct *work)
+{
+	struct ssh_rtl *rtl = to_ssh_rtl(work, rtx_timeout.reaper.work);
+	struct ssh_request *r, *n;
+	LIST_HEAD(claimed);
+	ktime_t now = ktime_get_coarse_boottime();
+	ktime_t timeout = rtl->rtx_timeout.timeout;
+	ktime_t next = KTIME_MAX;
+
+	trace_ssam_rtl_timeout_reap(atomic_read(&rtl->pending.count));
+
+	/*
+	 * Mark reaper as "not pending". This is done before checking any
+	 * requests to avoid lost-update type problems.
+	 */
+	spin_lock(&rtl->rtx_timeout.lock);
+	rtl->rtx_timeout.expires = KTIME_MAX;
+	spin_unlock(&rtl->rtx_timeout.lock);
+
+	spin_lock(&rtl->pending.lock);
+	list_for_each_entry_safe(r, n, &rtl->pending.head, node) {
+		ktime_t expires = ssh_request_get_expiration(r, timeout);
+
+		/*
+		 * Check if the timeout hasn't expired yet. Find out next
+		 * expiration date to be handled after this run.
+		 */
+		if (ktime_after(expires, now)) {
+			next = ktime_before(expires, next) ? expires : next;
+			continue;
+		}
+
+		/* Avoid further transitions if locked. */
+		if (test_and_set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state))
+			continue;
+
+		/*
+		 * We have now marked the packet as locked. Thus it cannot be
+		 * added to the pending or queued lists again after we've
+		 * removed it here. We can therefore re-use the node of this
+		 * packet temporarily.
+		 */
+
+		clear_bit(SSH_REQUEST_SF_PENDING_BIT, &r->state);
+
+		atomic_dec(&rtl->pending.count);
+		list_move_tail(&r->node, &claimed);
+	}
+	spin_unlock(&rtl->pending.lock);
+
+	/* Cancel and complete the request. */
+	list_for_each_entry_safe(r, n, &claimed, node) {
+		trace_ssam_request_timeout(r);
+
+		/*
+		 * At this point we've removed the packet from pending. This
+		 * means that we've obtained the last (only) reference of the
+		 * system to it. Thus we can just complete it.
+		 */
+		if (!test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+			ssh_rtl_complete_with_status(r, -ETIMEDOUT);
+
+		/*
+		 * Drop the reference we've obtained by removing it from the
+		 * pending set.
+		 */
+		list_del(&r->node);
+		ssh_request_put(r);
+	}
+
+	/* Ensure that the reaper doesn't run again immediately. */
+	next = max(next, ktime_add(now, SSH_RTL_REQUEST_TIMEOUT_RESOLUTION));
+	if (next != KTIME_MAX)
+		ssh_rtl_timeout_reaper_mod(rtl, now, next);
+
+	ssh_rtl_tx_schedule(rtl);
+}
+
+static void ssh_rtl_rx_event(struct ssh_rtl *rtl, const struct ssh_command *cmd,
+			     const struct ssam_span *data)
+{
+	trace_ssam_rx_event_received(cmd, data->len);
+
+	rtl_dbg(rtl, "rtl: handling event (rqid: %#06x)\n",
+		get_unaligned_le16(&cmd->rqid));
+
+	rtl->ops.handle_event(rtl, cmd, data);
+}
+
+static void ssh_rtl_rx_command(struct ssh_ptl *p, const struct ssam_span *data)
+{
+	struct ssh_rtl *rtl = to_ssh_rtl(p, ptl);
+	struct device *dev = &p->serdev->dev;
+	struct ssh_command *command;
+	struct ssam_span command_data;
+
+	if (sshp_parse_command(dev, data, &command, &command_data))
+		return;
+
+	/*
+	 * Check if the message was intended for us. If not, drop it.
+	 *
+	 * Note: We will need to change this to handle debug messages. On newer
+	 * generation devices, these seem to be sent to tid_out=0x03. We as
+	 * host can still receive them as they can be forwarded via an override
+	 * option on SAM, but doing so does not change tid_out=0x00.
+	 */
+	if (command->tid_out != 0x00) {
+		rtl_warn(rtl, "rtl: dropping message not intended for us (tid = %#04x)\n",
+			 command->tid_out);
+		return;
+	}
+
+	if (ssh_rqid_is_event(get_unaligned_le16(&command->rqid)))
+		ssh_rtl_rx_event(rtl, command, &command_data);
+	else
+		ssh_rtl_complete(rtl, command, &command_data);
+}
+
+static void ssh_rtl_rx_data(struct ssh_ptl *p, const struct ssam_span *data)
+{
+	if (!data->len) {
+		ptl_err(p, "rtl: rx: no data frame payload\n");
+		return;
+	}
+
+	switch (data->ptr[0]) {
+	case SSH_PLD_TYPE_CMD:
+		ssh_rtl_rx_command(p, data);
+		break;
+
+	default:
+		ptl_err(p, "rtl: rx: unknown frame payload type (type: %#04x)\n",
+			data->ptr[0]);
+		break;
+	}
+}
+
+static void ssh_rtl_packet_release(struct ssh_packet *p)
+{
+	struct ssh_request *rqst;
+
+	rqst = to_ssh_request(p);
+	rqst->ops->release(rqst);
+}
+
+static const struct ssh_packet_ops ssh_rtl_packet_ops = {
+	.complete = ssh_rtl_packet_callback,
+	.release = ssh_rtl_packet_release,
+};
+
+/**
+ * ssh_request_init() - Initialize SSH request.
+ * @rqst:  The request to initialize.
+ * @flags: Request flags, determining the type of the request.
+ * @ops:   Request operations.
+ *
+ * Initializes the given SSH request and underlying packet. Sets the message
+ * buffer pointer to %NULL and the message buffer length to zero. This buffer
+ * has to be set separately via ssh_request_set_data() before submission and
+ * must contain a valid SSH request message.
+ *
+ * Return: Returns zero on success or %-EINVAL if the given flags are invalid.
+ */
+int ssh_request_init(struct ssh_request *rqst, enum ssam_request_flags flags,
+		     const struct ssh_request_ops *ops)
+{
+	unsigned long type = BIT(SSH_PACKET_TY_BLOCKING_BIT);
+
+	/* Unsequenced requests cannot have a response. */
+	if (flags & SSAM_REQUEST_UNSEQUENCED && flags & SSAM_REQUEST_HAS_RESPONSE)
+		return -EINVAL;
+
+	if (!(flags & SSAM_REQUEST_UNSEQUENCED))
+		type |= BIT(SSH_PACKET_TY_SEQUENCED_BIT);
+
+	ssh_packet_init(&rqst->packet, type, SSH_PACKET_PRIORITY(DATA, 0),
+			&ssh_rtl_packet_ops);
+
+	INIT_LIST_HEAD(&rqst->node);
+
+	rqst->state = 0;
+	if (flags & SSAM_REQUEST_HAS_RESPONSE)
+		rqst->state |= BIT(SSH_REQUEST_TY_HAS_RESPONSE_BIT);
+
+	rqst->timestamp = KTIME_MAX;
+	rqst->ops = ops;
+
+	return 0;
+}
+
+/**
+ * ssh_rtl_init() - Initialize request transport layer.
+ * @rtl:    The request transport layer to initialize.
+ * @serdev: The underlying serial device, i.e. the lower-level transport.
+ * @ops:    Request transport layer operations.
+ *
+ * Initializes the given request transport layer and associated packet
+ * transport layer. Transmitter and receiver threads must be started
+ * separately via ssh_rtl_start(), after the request-layer has been
+ * initialized and the lower-level serial device layer has been set up.
+ *
+ * Return: Returns zero on success and a nonzero error code on failure.
+ */
+int ssh_rtl_init(struct ssh_rtl *rtl, struct serdev_device *serdev,
+		 const struct ssh_rtl_ops *ops)
+{
+	struct ssh_ptl_ops ptl_ops;
+	int status;
+
+	ptl_ops.data_received = ssh_rtl_rx_data;
+
+	status = ssh_ptl_init(&rtl->ptl, serdev, &ptl_ops);
+	if (status)
+		return status;
+
+	spin_lock_init(&rtl->queue.lock);
+	INIT_LIST_HEAD(&rtl->queue.head);
+
+	spin_lock_init(&rtl->pending.lock);
+	INIT_LIST_HEAD(&rtl->pending.head);
+	atomic_set_release(&rtl->pending.count, 0);
+
+	INIT_WORK(&rtl->tx.work, ssh_rtl_tx_work_fn);
+
+	spin_lock_init(&rtl->rtx_timeout.lock);
+	rtl->rtx_timeout.timeout = SSH_RTL_REQUEST_TIMEOUT;
+	rtl->rtx_timeout.expires = KTIME_MAX;
+	INIT_DELAYED_WORK(&rtl->rtx_timeout.reaper, ssh_rtl_timeout_reap);
+
+	rtl->ops = *ops;
+
+	return 0;
+}
+
+/**
+ * ssh_rtl_destroy() - Deinitialize request transport layer.
+ * @rtl: The request transport layer to deinitialize.
+ *
+ * Deinitializes the given request transport layer and frees resources
+ * associated with it. If receiver and/or transmitter threads have been
+ * started, the layer must first be shut down via ssh_rtl_shutdown() before
+ * this function can be called.
+ */
+void ssh_rtl_destroy(struct ssh_rtl *rtl)
+{
+	ssh_ptl_destroy(&rtl->ptl);
+}
+
+/**
+ * ssh_rtl_start() - Start request transmitter and receiver.
+ * @rtl: The request transport layer.
+ *
+ * Return: Returns zero on success, a negative error code on failure.
+ */
+int ssh_rtl_start(struct ssh_rtl *rtl)
+{
+	int status;
+
+	status = ssh_ptl_tx_start(&rtl->ptl);
+	if (status)
+		return status;
+
+	ssh_rtl_tx_schedule(rtl);
+
+	status = ssh_ptl_rx_start(&rtl->ptl);
+	if (status) {
+		ssh_rtl_flush(rtl, msecs_to_jiffies(5000));
+		ssh_ptl_tx_stop(&rtl->ptl);
+		return status;
+	}
+
+	return 0;
+}
+
+struct ssh_flush_request {
+	struct ssh_request base;
+	struct completion completion;
+	int status;
+};
+
+static void ssh_rtl_flush_request_complete(struct ssh_request *r,
+					   const struct ssh_command *cmd,
+					   const struct ssam_span *data,
+					   int status)
+{
+	struct ssh_flush_request *rqst;
+
+	rqst = container_of(r, struct ssh_flush_request, base);
+	rqst->status = status;
+}
+
+static void ssh_rtl_flush_request_release(struct ssh_request *r)
+{
+	struct ssh_flush_request *rqst;
+
+	rqst = container_of(r, struct ssh_flush_request, base);
+	complete_all(&rqst->completion);
+}
+
+static const struct ssh_request_ops ssh_rtl_flush_request_ops = {
+	.complete = ssh_rtl_flush_request_complete,
+	.release = ssh_rtl_flush_request_release,
+};
+
+/**
+ * ssh_rtl_flush() - Flush the request transport layer.
+ * @rtl:     request transport layer
+ * @timeout: timeout for the flush operation in jiffies
+ *
+ * Queue a special flush request and wait for its completion. This request
+ * will be completed after all other currently queued and pending requests
+ * have been completed. Instead of a normal data packet, this request submits
+ * a special flush packet, meaning that upon completion, also the underlying
+ * packet transport layer has been flushed.
+ *
+ * Flushing the request layer guarantees that all previously submitted
+ * requests have been fully completed before this call returns. Additionally,
+ * flushing blocks execution of all later submitted requests until the flush
+ * has been completed.
+ *
+ * If the caller ensures that no new requests are submitted after a call to
+ * this function, the request transport layer is guaranteed to have no
+ * remaining requests when this call returns. The same guarantee does not hold
+ * for the packet layer, on which control packets may still be queued after
+ * this call.
+ *
+ * Return: Returns zero on success, %-ETIMEDOUT if the flush timed out and has
+ * been canceled as a result of the timeout, or %-ESHUTDOWN if the packet
+ * and/or request transport layer has been shut down before this call. May
+ * also return %-EINTR if the underlying packet transmission has been
+ * interrupted.
+ */
+int ssh_rtl_flush(struct ssh_rtl *rtl, unsigned long timeout)
+{
+	const unsigned int init_flags = SSAM_REQUEST_UNSEQUENCED;
+	struct ssh_flush_request rqst;
+	int status;
+
+	ssh_request_init(&rqst.base, init_flags, &ssh_rtl_flush_request_ops);
+	rqst.base.packet.state |= BIT(SSH_PACKET_TY_FLUSH_BIT);
+	rqst.base.packet.priority = SSH_PACKET_PRIORITY(FLUSH, 0);
+	rqst.base.state |= BIT(SSH_REQUEST_TY_FLUSH_BIT);
+
+	init_completion(&rqst.completion);
+
+	status = ssh_rtl_submit(rtl, &rqst.base);
+	if (status)
+		return status;
+
+	ssh_request_put(&rqst.base);
+
+	if (!wait_for_completion_timeout(&rqst.completion, timeout)) {
+		ssh_rtl_cancel(&rqst.base, true);
+		wait_for_completion(&rqst.completion);
+	}
+
+	WARN_ON(rqst.status != 0 && rqst.status != -ECANCELED &&
+		rqst.status != -ESHUTDOWN && rqst.status != -EINTR);
+
+	return rqst.status == -ECANCELED ? -ETIMEDOUT : rqst.status;
+}
+
+/**
+ * ssh_rtl_shutdown() - Shut down request transport layer.
+ * @rtl: The request transport layer.
+ *
+ * Shuts down the request transport layer, removing and canceling all queued
+ * and pending requests. Requests canceled by this operation will be completed
+ * with %-ESHUTDOWN as status. Receiver and transmitter threads will be
+ * stopped, the lower-level packet layer will be shutdown.
+ *
+ * As a result of this function, the transport layer will be marked as shut
+ * down. Submission of requests after the transport layer has been shut down
+ * will fail with %-ESHUTDOWN.
+ */
+void ssh_rtl_shutdown(struct ssh_rtl *rtl)
+{
+	struct ssh_request *r, *n;
+	LIST_HEAD(claimed);
+	int pending;
+
+	set_bit(SSH_RTL_SF_SHUTDOWN_BIT, &rtl->state);
+	/*
+	 * Ensure that the layer gets marked as shut-down before actually
+	 * stopping it. In combination with the check in ssh_rtl_submit(),
+	 * this guarantees that no new requests can be added and all already
+	 * queued requests are properly canceled.
+	 */
+	smp_mb__after_atomic();
+
+	/* Remove requests from queue. */
+	spin_lock(&rtl->queue.lock);
+	list_for_each_entry_safe(r, n, &rtl->queue.head, node) {
+		set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state);
+		/* Ensure state never gets zero. */
+		smp_mb__before_atomic();
+		clear_bit(SSH_REQUEST_SF_QUEUED_BIT, &r->state);
+
+		list_move_tail(&r->node, &claimed);
+	}
+	spin_unlock(&rtl->queue.lock);
+
+	/*
+	 * We have now guaranteed that the queue is empty and no more new
+	 * requests can be submitted (i.e. it will stay empty). This means that
+	 * calling ssh_rtl_tx_schedule() will not schedule tx.work any more. So
+	 * we can simply call cancel_work_sync() on tx.work here and when that
+	 * returns, we've locked it down. This also means that after this call,
+	 * we don't submit any more packets to the underlying packet layer, so
+	 * we can also shut that down.
+	 */
+
+	cancel_work_sync(&rtl->tx.work);
+	ssh_ptl_shutdown(&rtl->ptl);
+	cancel_delayed_work_sync(&rtl->rtx_timeout.reaper);
+
+	/*
+	 * Shutting down the packet layer should also have canceled all
+	 * requests. Thus the pending set should be empty. Attempt to handle
+	 * this gracefully anyways, even though this should be dead code.
+	 */
+
+	pending = atomic_read(&rtl->pending.count);
+	if (WARN_ON(pending)) {
+		spin_lock(&rtl->pending.lock);
+		list_for_each_entry_safe(r, n, &rtl->pending.head, node) {
+			set_bit(SSH_REQUEST_SF_LOCKED_BIT, &r->state);
+			/* Ensure state never gets zero. */
+			smp_mb__before_atomic();
+			clear_bit(SSH_REQUEST_SF_PENDING_BIT, &r->state);
+
+			list_move_tail(&r->node, &claimed);
+		}
+		spin_unlock(&rtl->pending.lock);
+	}
+
+	/* Finally, cancel and complete the requests we claimed before. */
+	list_for_each_entry_safe(r, n, &claimed, node) {
+		/*
+		 * We need test_and_set() because we still might compete with
+		 * cancellation.
+		 */
+		if (!test_and_set_bit(SSH_REQUEST_SF_COMPLETED_BIT, &r->state))
+			ssh_rtl_complete_with_status(r, -ESHUTDOWN);
+
+		/*
+		 * Drop the reference we've obtained by removing it from the
+		 * lists.
+		 */
+		list_del(&r->node);
+		ssh_request_put(r);
+	}
+}
diff --git a/drivers/platform/surface/aggregator/ssh_request_layer.h b/drivers/platform/surface/aggregator/ssh_request_layer.h
new file mode 100644
index 000000000..4e387a031
--- /dev/null
+++ b/drivers/platform/surface/aggregator/ssh_request_layer.h
@@ -0,0 +1,143 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * SSH request transport layer.
+ *
+ * Copyright (C) 2019-2022 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#ifndef _SURFACE_AGGREGATOR_SSH_REQUEST_LAYER_H
+#define _SURFACE_AGGREGATOR_SSH_REQUEST_LAYER_H
+
+#include <linux/atomic.h>
+#include <linux/ktime.h>
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/workqueue.h>
+
+#include <linux/surface_aggregator/serial_hub.h>
+#include <linux/surface_aggregator/controller.h>
+
+#include "ssh_packet_layer.h"
+
+/**
+ * enum ssh_rtl_state_flags - State-flags for &struct ssh_rtl.
+ *
+ * @SSH_RTL_SF_SHUTDOWN_BIT:
+ *	Indicates that the request transport layer has been shut down or is
+ *	being shut down and should not accept any new requests.
+ */
+enum ssh_rtl_state_flags {
+	SSH_RTL_SF_SHUTDOWN_BIT,
+};
+
+/**
+ * struct ssh_rtl_ops - Callback operations for request transport layer.
+ * @handle_event: Function called when a SSH event has been received. The
+ *                specified function takes the request layer, received command
+ *                struct, and corresponding payload as arguments. If the event
+ *                has no payload, the payload span is empty (not %NULL).
+ */
+struct ssh_rtl_ops {
+	void (*handle_event)(struct ssh_rtl *rtl, const struct ssh_command *cmd,
+			     const struct ssam_span *data);
+};
+
+/**
+ * struct ssh_rtl - SSH request transport layer.
+ * @ptl:           Underlying packet transport layer.
+ * @state:         State(-flags) of the transport layer.
+ * @queue:         Request submission queue.
+ * @queue.lock:    Lock for modifying the request submission queue.
+ * @queue.head:    List-head of the request submission queue.
+ * @pending:       Set/list of pending requests.
+ * @pending.lock:  Lock for modifying the request set.
+ * @pending.head:  List-head of the pending set/list.
+ * @pending.count: Number of currently pending requests.
+ * @tx:            Transmitter subsystem.
+ * @tx.work:       Transmitter work item.
+ * @rtx_timeout:   Retransmission timeout subsystem.
+ * @rtx_timeout.lock:    Lock for modifying the retransmission timeout reaper.
+ * @rtx_timeout.timeout: Timeout interval for retransmission.
+ * @rtx_timeout.expires: Time specifying when the reaper work is next scheduled.
+ * @rtx_timeout.reaper:  Work performing timeout checks and subsequent actions.
+ * @ops:           Request layer operations.
+ */
+struct ssh_rtl {
+	struct ssh_ptl ptl;
+	unsigned long state;
+
+	struct {
+		spinlock_t lock;
+		struct list_head head;
+	} queue;
+
+	struct {
+		spinlock_t lock;
+		struct list_head head;
+		atomic_t count;
+	} pending;
+
+	struct {
+		struct work_struct work;
+	} tx;
+
+	struct {
+		spinlock_t lock;
+		ktime_t timeout;
+		ktime_t expires;
+		struct delayed_work reaper;
+	} rtx_timeout;
+
+	struct ssh_rtl_ops ops;
+};
+
+#define rtl_dbg(r, fmt, ...)  ptl_dbg(&(r)->ptl, fmt, ##__VA_ARGS__)
+#define rtl_info(p, fmt, ...) ptl_info(&(p)->ptl, fmt, ##__VA_ARGS__)
+#define rtl_warn(r, fmt, ...) ptl_warn(&(r)->ptl, fmt, ##__VA_ARGS__)
+#define rtl_err(r, fmt, ...)  ptl_err(&(r)->ptl, fmt, ##__VA_ARGS__)
+#define rtl_dbg_cond(r, fmt, ...) __ssam_prcond(rtl_dbg, r, fmt, ##__VA_ARGS__)
+
+#define to_ssh_rtl(ptr, member) \
+	container_of(ptr, struct ssh_rtl, member)
+
+/**
+ * ssh_rtl_get_device() - Get device associated with request transport layer.
+ * @rtl: The request transport layer.
+ *
+ * Return: Returns the device on which the given request transport layer
+ * builds upon.
+ */
+static inline struct device *ssh_rtl_get_device(struct ssh_rtl *rtl)
+{
+	return ssh_ptl_get_device(&rtl->ptl);
+}
+
+/**
+ * ssh_request_rtl() - Get request transport layer associated with request.
+ * @rqst: The request to get the request transport layer reference for.
+ *
+ * Return: Returns the &struct ssh_rtl associated with the given SSH request.
+ */
+static inline struct ssh_rtl *ssh_request_rtl(struct ssh_request *rqst)
+{
+	struct ssh_ptl *ptl;
+
+	ptl = READ_ONCE(rqst->packet.ptl);
+	return likely(ptl) ? to_ssh_rtl(ptl, ptl) : NULL;
+}
+
+int ssh_rtl_submit(struct ssh_rtl *rtl, struct ssh_request *rqst);
+bool ssh_rtl_cancel(struct ssh_request *rqst, bool pending);
+
+int ssh_rtl_init(struct ssh_rtl *rtl, struct serdev_device *serdev,
+		 const struct ssh_rtl_ops *ops);
+
+int ssh_rtl_start(struct ssh_rtl *rtl);
+int ssh_rtl_flush(struct ssh_rtl *rtl, unsigned long timeout);
+void ssh_rtl_shutdown(struct ssh_rtl *rtl);
+void ssh_rtl_destroy(struct ssh_rtl *rtl);
+
+int ssh_request_init(struct ssh_request *rqst, enum ssam_request_flags flags,
+		     const struct ssh_request_ops *ops);
+
+#endif /* _SURFACE_AGGREGATOR_SSH_REQUEST_LAYER_H */
diff --git a/drivers/platform/surface/aggregator/trace.h b/drivers/platform/surface/aggregator/trace.h
new file mode 100644
index 000000000..2a2c17771
--- /dev/null
+++ b/drivers/platform/surface/aggregator/trace.h
@@ -0,0 +1,642 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Trace points for SSAM/SSH.
+ *
+ * Copyright (C) 2020-2022 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM surface_aggregator
+
+#if !defined(_SURFACE_AGGREGATOR_TRACE_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _SURFACE_AGGREGATOR_TRACE_H
+
+#include <linux/surface_aggregator/serial_hub.h>
+
+#include <asm/unaligned.h>
+#include <linux/tracepoint.h>
+
+TRACE_DEFINE_ENUM(SSH_FRAME_TYPE_DATA_SEQ);
+TRACE_DEFINE_ENUM(SSH_FRAME_TYPE_DATA_NSQ);
+TRACE_DEFINE_ENUM(SSH_FRAME_TYPE_ACK);
+TRACE_DEFINE_ENUM(SSH_FRAME_TYPE_NAK);
+
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_LOCKED_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_QUEUED_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_PENDING_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_TRANSMITTING_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_TRANSMITTED_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_ACKED_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_CANCELED_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_SF_COMPLETED_BIT);
+
+TRACE_DEFINE_ENUM(SSH_PACKET_TY_FLUSH_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_TY_SEQUENCED_BIT);
+TRACE_DEFINE_ENUM(SSH_PACKET_TY_BLOCKING_BIT);
+
+TRACE_DEFINE_ENUM(SSH_PACKET_FLAGS_SF_MASK);
+TRACE_DEFINE_ENUM(SSH_PACKET_FLAGS_TY_MASK);
+
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_LOCKED_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_QUEUED_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_PENDING_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_TRANSMITTING_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_TRANSMITTED_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_RSPRCVD_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_CANCELED_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_SF_COMPLETED_BIT);
+
+TRACE_DEFINE_ENUM(SSH_REQUEST_TY_FLUSH_BIT);
+TRACE_DEFINE_ENUM(SSH_REQUEST_TY_HAS_RESPONSE_BIT);
+
+TRACE_DEFINE_ENUM(SSH_REQUEST_FLAGS_SF_MASK);
+TRACE_DEFINE_ENUM(SSH_REQUEST_FLAGS_TY_MASK);
+
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_SAM);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_BAT);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_TMP);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_PMC);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_FAN);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_PoM);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_DBG);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_KBD);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_FWU);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_UNI);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_LPC);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_TCL);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_SFL);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_KIP);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_EXT);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_BLD);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_BAS);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_SEN);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_SRQ);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_MCU);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_HID);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_TCH);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_BKL);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_TAM);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_ACC0);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_UFI);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_USC);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_PEN);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_VID);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_AUD);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_SMC);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_KPD);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_REG);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_SPT);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_SYS);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_ACC1);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_SHB);
+TRACE_DEFINE_ENUM(SSAM_SSH_TC_POS);
+
+#define SSAM_PTR_UID_LEN		9
+#define SSAM_U8_FIELD_NOT_APPLICABLE	((u16)-1)
+#define SSAM_SEQ_NOT_APPLICABLE		((u16)-1)
+#define SSAM_RQID_NOT_APPLICABLE	((u32)-1)
+#define SSAM_SSH_TC_NOT_APPLICABLE	0
+
+#ifndef _SURFACE_AGGREGATOR_TRACE_HELPERS
+#define _SURFACE_AGGREGATOR_TRACE_HELPERS
+
+/**
+ * ssam_trace_ptr_uid() - Convert the pointer to a non-pointer UID string.
+ * @ptr: The pointer to convert.
+ * @uid_str: A buffer of length SSAM_PTR_UID_LEN where the UID will be stored.
+ *
+ * Converts the given pointer into a UID string that is safe to be shared
+ * with userspace and logs, i.e. doesn't give away the real memory location.
+ */
+static inline void ssam_trace_ptr_uid(const void *ptr, char *uid_str)
+{
+	char buf[2 * sizeof(void *) + 1];
+
+	BUILD_BUG_ON(ARRAY_SIZE(buf) < SSAM_PTR_UID_LEN);
+
+	snprintf(buf, ARRAY_SIZE(buf), "%p", ptr);
+	memcpy(uid_str, &buf[ARRAY_SIZE(buf) - SSAM_PTR_UID_LEN],
+	       SSAM_PTR_UID_LEN);
+}
+
+/**
+ * ssam_trace_get_packet_seq() - Read the packet's sequence ID.
+ * @p: The packet.
+ *
+ * Return: Returns the packet's sequence ID (SEQ) field if present, or
+ * %SSAM_SEQ_NOT_APPLICABLE if not (e.g. flush packet).
+ */
+static inline u16 ssam_trace_get_packet_seq(const struct ssh_packet *p)
+{
+	if (!p->data.ptr || p->data.len < SSH_MESSAGE_LENGTH(0))
+		return SSAM_SEQ_NOT_APPLICABLE;
+
+	return p->data.ptr[SSH_MSGOFFSET_FRAME(seq)];
+}
+
+/**
+ * ssam_trace_get_request_id() - Read the packet's request ID.
+ * @p: The packet.
+ *
+ * Return: Returns the packet's request ID (RQID) field if the packet
+ * represents a request with command data, or %SSAM_RQID_NOT_APPLICABLE if not
+ * (e.g. flush request, control packet).
+ */
+static inline u32 ssam_trace_get_request_id(const struct ssh_packet *p)
+{
+	if (!p->data.ptr || p->data.len < SSH_COMMAND_MESSAGE_LENGTH(0))
+		return SSAM_RQID_NOT_APPLICABLE;
+
+	return get_unaligned_le16(&p->data.ptr[SSH_MSGOFFSET_COMMAND(rqid)]);
+}
+
+/**
+ * ssam_trace_get_request_tc() - Read the packet's request target category.
+ * @p: The packet.
+ *
+ * Return: Returns the packet's request target category (TC) field if the
+ * packet represents a request with command data, or %SSAM_TC_NOT_APPLICABLE
+ * if not (e.g. flush request, control packet).
+ */
+static inline u32 ssam_trace_get_request_tc(const struct ssh_packet *p)
+{
+	if (!p->data.ptr || p->data.len < SSH_COMMAND_MESSAGE_LENGTH(0))
+		return SSAM_SSH_TC_NOT_APPLICABLE;
+
+	return get_unaligned_le16(&p->data.ptr[SSH_MSGOFFSET_COMMAND(tc)]);
+}
+
+#endif /* _SURFACE_AGGREGATOR_TRACE_HELPERS */
+
+#define ssam_trace_get_command_field_u8(packet, field) \
+	((!(packet) || (packet)->data.len < SSH_COMMAND_MESSAGE_LENGTH(0)) \
+	 ? 0 : (packet)->data.ptr[SSH_MSGOFFSET_COMMAND(field)])
+
+#define ssam_show_generic_u8_field(value)				\
+	__print_symbolic(value,						\
+		{ SSAM_U8_FIELD_NOT_APPLICABLE,		"N/A" }		\
+	)
+
+#define ssam_show_frame_type(ty)					\
+	__print_symbolic(ty,						\
+		{ SSH_FRAME_TYPE_DATA_SEQ,		"DSEQ" },	\
+		{ SSH_FRAME_TYPE_DATA_NSQ,		"DNSQ" },	\
+		{ SSH_FRAME_TYPE_ACK,			"ACK"  },	\
+		{ SSH_FRAME_TYPE_NAK,			"NAK"  }	\
+	)
+
+#define ssam_show_packet_type(type)					\
+	__print_flags(flags & SSH_PACKET_FLAGS_TY_MASK, "",		\
+		{ BIT(SSH_PACKET_TY_FLUSH_BIT),		"F" },		\
+		{ BIT(SSH_PACKET_TY_SEQUENCED_BIT),	"S" },		\
+		{ BIT(SSH_PACKET_TY_BLOCKING_BIT),	"B" }		\
+	)
+
+#define ssam_show_packet_state(state)					\
+	__print_flags(flags & SSH_PACKET_FLAGS_SF_MASK, "",		\
+		{ BIT(SSH_PACKET_SF_LOCKED_BIT),	"L" },		\
+		{ BIT(SSH_PACKET_SF_QUEUED_BIT),	"Q" },		\
+		{ BIT(SSH_PACKET_SF_PENDING_BIT),	"P" },		\
+		{ BIT(SSH_PACKET_SF_TRANSMITTING_BIT),	"S" },		\
+		{ BIT(SSH_PACKET_SF_TRANSMITTED_BIT),	"T" },		\
+		{ BIT(SSH_PACKET_SF_ACKED_BIT),		"A" },		\
+		{ BIT(SSH_PACKET_SF_CANCELED_BIT),	"C" },		\
+		{ BIT(SSH_PACKET_SF_COMPLETED_BIT),	"F" }		\
+	)
+
+#define ssam_show_packet_seq(seq)					\
+	__print_symbolic(seq,						\
+		{ SSAM_SEQ_NOT_APPLICABLE,		"N/A" }		\
+	)
+
+#define ssam_show_request_type(flags)					\
+	__print_flags((flags) & SSH_REQUEST_FLAGS_TY_MASK, "",		\
+		{ BIT(SSH_REQUEST_TY_FLUSH_BIT),	"F" },		\
+		{ BIT(SSH_REQUEST_TY_HAS_RESPONSE_BIT),	"R" }		\
+	)
+
+#define ssam_show_request_state(flags)					\
+	__print_flags((flags) & SSH_REQUEST_FLAGS_SF_MASK, "",		\
+		{ BIT(SSH_REQUEST_SF_LOCKED_BIT),	"L" },		\
+		{ BIT(SSH_REQUEST_SF_QUEUED_BIT),	"Q" },		\
+		{ BIT(SSH_REQUEST_SF_PENDING_BIT),	"P" },		\
+		{ BIT(SSH_REQUEST_SF_TRANSMITTING_BIT),	"S" },		\
+		{ BIT(SSH_REQUEST_SF_TRANSMITTED_BIT),	"T" },		\
+		{ BIT(SSH_REQUEST_SF_RSPRCVD_BIT),	"A" },		\
+		{ BIT(SSH_REQUEST_SF_CANCELED_BIT),	"C" },		\
+		{ BIT(SSH_REQUEST_SF_COMPLETED_BIT),	"F" }		\
+	)
+
+#define ssam_show_request_id(rqid)					\
+	__print_symbolic(rqid,						\
+		{ SSAM_RQID_NOT_APPLICABLE,		"N/A" }		\
+	)
+
+#define ssam_show_ssh_tc(rqid)						\
+	__print_symbolic(rqid,						\
+		{ SSAM_SSH_TC_NOT_APPLICABLE,		"N/A"  },	\
+		{ SSAM_SSH_TC_SAM,			"SAM"  },	\
+		{ SSAM_SSH_TC_BAT,			"BAT"  },	\
+		{ SSAM_SSH_TC_TMP,			"TMP"  },	\
+		{ SSAM_SSH_TC_PMC,			"PMC"  },	\
+		{ SSAM_SSH_TC_FAN,			"FAN"  },	\
+		{ SSAM_SSH_TC_PoM,			"PoM"  },	\
+		{ SSAM_SSH_TC_DBG,			"DBG"  },	\
+		{ SSAM_SSH_TC_KBD,			"KBD"  },	\
+		{ SSAM_SSH_TC_FWU,			"FWU"  },	\
+		{ SSAM_SSH_TC_UNI,			"UNI"  },	\
+		{ SSAM_SSH_TC_LPC,			"LPC"  },	\
+		{ SSAM_SSH_TC_TCL,			"TCL"  },	\
+		{ SSAM_SSH_TC_SFL,			"SFL"  },	\
+		{ SSAM_SSH_TC_KIP,			"KIP"  },	\
+		{ SSAM_SSH_TC_EXT,			"EXT"  },	\
+		{ SSAM_SSH_TC_BLD,			"BLD"  },	\
+		{ SSAM_SSH_TC_BAS,			"BAS"  },	\
+		{ SSAM_SSH_TC_SEN,			"SEN"  },	\
+		{ SSAM_SSH_TC_SRQ,			"SRQ"  },	\
+		{ SSAM_SSH_TC_MCU,			"MCU"  },	\
+		{ SSAM_SSH_TC_HID,			"HID"  },	\
+		{ SSAM_SSH_TC_TCH,			"TCH"  },	\
+		{ SSAM_SSH_TC_BKL,			"BKL"  },	\
+		{ SSAM_SSH_TC_TAM,			"TAM"  },	\
+		{ SSAM_SSH_TC_ACC0,			"ACC0" },	\
+		{ SSAM_SSH_TC_UFI,			"UFI"  },	\
+		{ SSAM_SSH_TC_USC,			"USC"  },	\
+		{ SSAM_SSH_TC_PEN,			"PEN"  },	\
+		{ SSAM_SSH_TC_VID,			"VID"  },	\
+		{ SSAM_SSH_TC_AUD,			"AUD"  },	\
+		{ SSAM_SSH_TC_SMC,			"SMC"  },	\
+		{ SSAM_SSH_TC_KPD,			"KPD"  },	\
+		{ SSAM_SSH_TC_REG,			"REG"  },	\
+		{ SSAM_SSH_TC_SPT,			"SPT"  },	\
+		{ SSAM_SSH_TC_SYS,			"SYS"  },	\
+		{ SSAM_SSH_TC_ACC1,			"ACC1" },	\
+		{ SSAM_SSH_TC_SHB,			"SMB"  },	\
+		{ SSAM_SSH_TC_POS,			"POS"  }	\
+	)
+
+DECLARE_EVENT_CLASS(ssam_frame_class,
+	TP_PROTO(const struct ssh_frame *frame),
+
+	TP_ARGS(frame),
+
+	TP_STRUCT__entry(
+		__field(u8, type)
+		__field(u8, seq)
+		__field(u16, len)
+	),
+
+	TP_fast_assign(
+		__entry->type = frame->type;
+		__entry->seq = frame->seq;
+		__entry->len = get_unaligned_le16(&frame->len);
+	),
+
+	TP_printk("ty=%s, seq=%#04x, len=%u",
+		ssam_show_frame_type(__entry->type),
+		__entry->seq,
+		__entry->len
+	)
+);
+
+#define DEFINE_SSAM_FRAME_EVENT(name)				\
+	DEFINE_EVENT(ssam_frame_class, ssam_##name,		\
+		TP_PROTO(const struct ssh_frame *frame),	\
+		TP_ARGS(frame)					\
+	)
+
+DECLARE_EVENT_CLASS(ssam_command_class,
+	TP_PROTO(const struct ssh_command *cmd, u16 len),
+
+	TP_ARGS(cmd, len),
+
+	TP_STRUCT__entry(
+		__field(u16, rqid)
+		__field(u16, len)
+		__field(u8, tc)
+		__field(u8, cid)
+		__field(u8, iid)
+	),
+
+	TP_fast_assign(
+		__entry->rqid = get_unaligned_le16(&cmd->rqid);
+		__entry->tc = cmd->tc;
+		__entry->cid = cmd->cid;
+		__entry->iid = cmd->iid;
+		__entry->len = len;
+	),
+
+	TP_printk("rqid=%#06x, tc=%s, cid=%#04x, iid=%#04x, len=%u",
+		__entry->rqid,
+		ssam_show_ssh_tc(__entry->tc),
+		__entry->cid,
+		__entry->iid,
+		__entry->len
+	)
+);
+
+#define DEFINE_SSAM_COMMAND_EVENT(name)					\
+	DEFINE_EVENT(ssam_command_class, ssam_##name,			\
+		TP_PROTO(const struct ssh_command *cmd, u16 len),	\
+		TP_ARGS(cmd, len)					\
+	)
+
+DECLARE_EVENT_CLASS(ssam_packet_class,
+	TP_PROTO(const struct ssh_packet *packet),
+
+	TP_ARGS(packet),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, state)
+		__array(char, uid, SSAM_PTR_UID_LEN)
+		__field(u8, priority)
+		__field(u16, length)
+		__field(u16, seq)
+	),
+
+	TP_fast_assign(
+		__entry->state = READ_ONCE(packet->state);
+		ssam_trace_ptr_uid(packet, __entry->uid);
+		__entry->priority = READ_ONCE(packet->priority);
+		__entry->length = packet->data.len;
+		__entry->seq = ssam_trace_get_packet_seq(packet);
+	),
+
+	TP_printk("uid=%s, seq=%s, ty=%s, pri=%#04x, len=%u, sta=%s",
+		__entry->uid,
+		ssam_show_packet_seq(__entry->seq),
+		ssam_show_packet_type(__entry->state),
+		__entry->priority,
+		__entry->length,
+		ssam_show_packet_state(__entry->state)
+	)
+);
+
+#define DEFINE_SSAM_PACKET_EVENT(name)				\
+	DEFINE_EVENT(ssam_packet_class, ssam_##name,		\
+		TP_PROTO(const struct ssh_packet *packet),	\
+		TP_ARGS(packet)					\
+	)
+
+DECLARE_EVENT_CLASS(ssam_packet_status_class,
+	TP_PROTO(const struct ssh_packet *packet, int status),
+
+	TP_ARGS(packet, status),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, state)
+		__field(int, status)
+		__array(char, uid, SSAM_PTR_UID_LEN)
+		__field(u8, priority)
+		__field(u16, length)
+		__field(u16, seq)
+	),
+
+	TP_fast_assign(
+		__entry->state = READ_ONCE(packet->state);
+		__entry->status = status;
+		ssam_trace_ptr_uid(packet, __entry->uid);
+		__entry->priority = READ_ONCE(packet->priority);
+		__entry->length = packet->data.len;
+		__entry->seq = ssam_trace_get_packet_seq(packet);
+	),
+
+	TP_printk("uid=%s, seq=%s, ty=%s, pri=%#04x, len=%u, sta=%s, status=%d",
+		__entry->uid,
+		ssam_show_packet_seq(__entry->seq),
+		ssam_show_packet_type(__entry->state),
+		__entry->priority,
+		__entry->length,
+		ssam_show_packet_state(__entry->state),
+		__entry->status
+	)
+);
+
+#define DEFINE_SSAM_PACKET_STATUS_EVENT(name)				\
+	DEFINE_EVENT(ssam_packet_status_class, ssam_##name,		\
+		TP_PROTO(const struct ssh_packet *packet, int status),	\
+		TP_ARGS(packet, status)					\
+	)
+
+DECLARE_EVENT_CLASS(ssam_request_class,
+	TP_PROTO(const struct ssh_request *request),
+
+	TP_ARGS(request),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, state)
+		__field(u32, rqid)
+		__array(char, uid, SSAM_PTR_UID_LEN)
+		__field(u8, tc)
+		__field(u16, cid)
+		__field(u16, iid)
+	),
+
+	TP_fast_assign(
+		const struct ssh_packet *p = &request->packet;
+
+		/* Use packet for UID so we can match requests to packets. */
+		__entry->state = READ_ONCE(request->state);
+		__entry->rqid = ssam_trace_get_request_id(p);
+		ssam_trace_ptr_uid(p, __entry->uid);
+		__entry->tc = ssam_trace_get_request_tc(p);
+		__entry->cid = ssam_trace_get_command_field_u8(p, cid);
+		__entry->iid = ssam_trace_get_command_field_u8(p, iid);
+	),
+
+	TP_printk("uid=%s, rqid=%s, ty=%s, sta=%s, tc=%s, cid=%s, iid=%s",
+		__entry->uid,
+		ssam_show_request_id(__entry->rqid),
+		ssam_show_request_type(__entry->state),
+		ssam_show_request_state(__entry->state),
+		ssam_show_ssh_tc(__entry->tc),
+		ssam_show_generic_u8_field(__entry->cid),
+		ssam_show_generic_u8_field(__entry->iid)
+	)
+);
+
+#define DEFINE_SSAM_REQUEST_EVENT(name)				\
+	DEFINE_EVENT(ssam_request_class, ssam_##name,		\
+		TP_PROTO(const struct ssh_request *request),	\
+		TP_ARGS(request)				\
+	)
+
+DECLARE_EVENT_CLASS(ssam_request_status_class,
+	TP_PROTO(const struct ssh_request *request, int status),
+
+	TP_ARGS(request, status),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, state)
+		__field(u32, rqid)
+		__field(int, status)
+		__array(char, uid, SSAM_PTR_UID_LEN)
+		__field(u8, tc)
+		__field(u16, cid)
+		__field(u16, iid)
+	),
+
+	TP_fast_assign(
+		const struct ssh_packet *p = &request->packet;
+
+		/* Use packet for UID so we can match requests to packets. */
+		__entry->state = READ_ONCE(request->state);
+		__entry->rqid = ssam_trace_get_request_id(p);
+		__entry->status = status;
+		ssam_trace_ptr_uid(p, __entry->uid);
+		__entry->tc = ssam_trace_get_request_tc(p);
+		__entry->cid = ssam_trace_get_command_field_u8(p, cid);
+		__entry->iid = ssam_trace_get_command_field_u8(p, iid);
+	),
+
+	TP_printk("uid=%s, rqid=%s, ty=%s, sta=%s, tc=%s, cid=%s, iid=%s, status=%d",
+		__entry->uid,
+		ssam_show_request_id(__entry->rqid),
+		ssam_show_request_type(__entry->state),
+		ssam_show_request_state(__entry->state),
+		ssam_show_ssh_tc(__entry->tc),
+		ssam_show_generic_u8_field(__entry->cid),
+		ssam_show_generic_u8_field(__entry->iid),
+		__entry->status
+	)
+);
+
+#define DEFINE_SSAM_REQUEST_STATUS_EVENT(name)				\
+	DEFINE_EVENT(ssam_request_status_class, ssam_##name,		\
+		TP_PROTO(const struct ssh_request *request, int status),\
+		TP_ARGS(request, status)				\
+	)
+
+DECLARE_EVENT_CLASS(ssam_alloc_class,
+	TP_PROTO(void *ptr, size_t len),
+
+	TP_ARGS(ptr, len),
+
+	TP_STRUCT__entry(
+		__field(size_t, len)
+		__array(char, uid, SSAM_PTR_UID_LEN)
+	),
+
+	TP_fast_assign(
+		__entry->len = len;
+		ssam_trace_ptr_uid(ptr, __entry->uid);
+	),
+
+	TP_printk("uid=%s, len=%zu", __entry->uid, __entry->len)
+);
+
+#define DEFINE_SSAM_ALLOC_EVENT(name)					\
+	DEFINE_EVENT(ssam_alloc_class, ssam_##name,			\
+		TP_PROTO(void *ptr, size_t len),			\
+		TP_ARGS(ptr, len)					\
+	)
+
+DECLARE_EVENT_CLASS(ssam_free_class,
+	TP_PROTO(void *ptr),
+
+	TP_ARGS(ptr),
+
+	TP_STRUCT__entry(
+		__array(char, uid, SSAM_PTR_UID_LEN)
+	),
+
+	TP_fast_assign(
+		ssam_trace_ptr_uid(ptr, __entry->uid);
+	),
+
+	TP_printk("uid=%s", __entry->uid)
+);
+
+#define DEFINE_SSAM_FREE_EVENT(name)					\
+	DEFINE_EVENT(ssam_free_class, ssam_##name,			\
+		TP_PROTO(void *ptr),					\
+		TP_ARGS(ptr)						\
+	)
+
+DECLARE_EVENT_CLASS(ssam_pending_class,
+	TP_PROTO(unsigned int pending),
+
+	TP_ARGS(pending),
+
+	TP_STRUCT__entry(
+		__field(unsigned int, pending)
+	),
+
+	TP_fast_assign(
+		__entry->pending = pending;
+	),
+
+	TP_printk("pending=%u", __entry->pending)
+);
+
+#define DEFINE_SSAM_PENDING_EVENT(name)					\
+	DEFINE_EVENT(ssam_pending_class, ssam_##name,			\
+		TP_PROTO(unsigned int pending),				\
+		TP_ARGS(pending)					\
+	)
+
+DECLARE_EVENT_CLASS(ssam_data_class,
+	TP_PROTO(size_t length),
+
+	TP_ARGS(length),
+
+	TP_STRUCT__entry(
+		__field(size_t, length)
+	),
+
+	TP_fast_assign(
+		__entry->length = length;
+	),
+
+	TP_printk("length=%zu", __entry->length)
+);
+
+#define DEFINE_SSAM_DATA_EVENT(name)					\
+	DEFINE_EVENT(ssam_data_class, ssam_##name,			\
+		TP_PROTO(size_t length),				\
+		TP_ARGS(length)						\
+	)
+
+DEFINE_SSAM_FRAME_EVENT(rx_frame_received);
+DEFINE_SSAM_COMMAND_EVENT(rx_response_received);
+DEFINE_SSAM_COMMAND_EVENT(rx_event_received);
+
+DEFINE_SSAM_PACKET_EVENT(packet_release);
+DEFINE_SSAM_PACKET_EVENT(packet_submit);
+DEFINE_SSAM_PACKET_EVENT(packet_resubmit);
+DEFINE_SSAM_PACKET_EVENT(packet_timeout);
+DEFINE_SSAM_PACKET_EVENT(packet_cancel);
+DEFINE_SSAM_PACKET_STATUS_EVENT(packet_complete);
+DEFINE_SSAM_PENDING_EVENT(ptl_timeout_reap);
+
+DEFINE_SSAM_REQUEST_EVENT(request_submit);
+DEFINE_SSAM_REQUEST_EVENT(request_timeout);
+DEFINE_SSAM_REQUEST_EVENT(request_cancel);
+DEFINE_SSAM_REQUEST_STATUS_EVENT(request_complete);
+DEFINE_SSAM_PENDING_EVENT(rtl_timeout_reap);
+
+DEFINE_SSAM_PACKET_EVENT(ei_tx_drop_ack_packet);
+DEFINE_SSAM_PACKET_EVENT(ei_tx_drop_nak_packet);
+DEFINE_SSAM_PACKET_EVENT(ei_tx_drop_dsq_packet);
+DEFINE_SSAM_PACKET_STATUS_EVENT(ei_tx_fail_write);
+DEFINE_SSAM_PACKET_EVENT(ei_tx_corrupt_data);
+DEFINE_SSAM_DATA_EVENT(ei_rx_corrupt_syn);
+DEFINE_SSAM_FRAME_EVENT(ei_rx_corrupt_data);
+DEFINE_SSAM_REQUEST_EVENT(ei_rx_drop_response);
+
+DEFINE_SSAM_ALLOC_EVENT(ctrl_packet_alloc);
+DEFINE_SSAM_FREE_EVENT(ctrl_packet_free);
+
+DEFINE_SSAM_ALLOC_EVENT(event_item_alloc);
+DEFINE_SSAM_FREE_EVENT(event_item_free);
+
+#endif /* _SURFACE_AGGREGATOR_TRACE_H */
+
+/* This part must be outside protection */
+#undef TRACE_INCLUDE_PATH
+#undef TRACE_INCLUDE_FILE
+
+#define TRACE_INCLUDE_PATH .
+#define TRACE_INCLUDE_FILE trace
+
+#include <trace/define_trace.h>