Adding upstream version 6.1.76.upstream/6.1.76upstream

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

1 files changed, 397 insertions, 0 deletions

diff --git a/Documentation/driver-api/surface_aggregator/client.rst b/Documentation/driver-api/surface_aggregator/client.rst
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+.. SPDX-License-Identifier: GPL-2.0+
+
+.. |ssam_controller| replace:: :c:type:`struct ssam_controller <ssam_controller>`
+.. |ssam_device| replace:: :c:type:`struct ssam_device <ssam_device>`
+.. |ssam_device_driver| replace:: :c:type:`struct ssam_device_driver <ssam_device_driver>`
+.. |ssam_client_bind| replace:: :c:func:`ssam_client_bind`
+.. |ssam_client_link| replace:: :c:func:`ssam_client_link`
+.. |ssam_get_controller| replace:: :c:func:`ssam_get_controller`
+.. |ssam_controller_get| replace:: :c:func:`ssam_controller_get`
+.. |ssam_controller_put| replace:: :c:func:`ssam_controller_put`
+.. |ssam_device_alloc| replace:: :c:func:`ssam_device_alloc`
+.. |ssam_device_add| replace:: :c:func:`ssam_device_add`
+.. |ssam_device_remove| replace:: :c:func:`ssam_device_remove`
+.. |ssam_device_driver_register| replace:: :c:func:`ssam_device_driver_register`
+.. |ssam_device_driver_unregister| replace:: :c:func:`ssam_device_driver_unregister`
+.. |module_ssam_device_driver| replace:: :c:func:`module_ssam_device_driver`
+.. |SSAM_DEVICE| replace:: :c:func:`SSAM_DEVICE`
+.. |ssam_notifier_register| replace:: :c:func:`ssam_notifier_register`
+.. |ssam_notifier_unregister| replace:: :c:func:`ssam_notifier_unregister`
+.. |ssam_device_notifier_register| replace:: :c:func:`ssam_device_notifier_register`
+.. |ssam_device_notifier_unregister| replace:: :c:func:`ssam_device_notifier_unregister`
+.. |ssam_request_sync| replace:: :c:func:`ssam_request_sync`
+.. |ssam_event_mask| replace:: :c:type:`enum ssam_event_mask <ssam_event_mask>`
+
+
+======================
+Writing Client Drivers
+======================
+
+For the API documentation, refer to:
+
+.. toctree::
+   :maxdepth: 2
+
+   client-api
+
+
+Overview
+========
+
+Client drivers can be set up in two main ways, depending on how the
+corresponding device is made available to the system. We specifically
+differentiate between devices that are presented to the system via one of
+the conventional ways, e.g. as platform devices via ACPI, and devices that
+are non-discoverable and instead need to be explicitly provided by some
+other mechanism, as discussed further below.
+
+
+Non-SSAM Client Drivers
+=======================
+
+All communication with the SAM EC is handled via the |ssam_controller|
+representing that EC to the kernel. Drivers targeting a non-SSAM device (and
+thus not being a |ssam_device_driver|) need to explicitly establish a
+connection/relation to that controller. This can be done via the
+|ssam_client_bind| function. Said function returns a reference to the SSAM
+controller, but, more importantly, also establishes a device link between
+client device and controller (this can also be done separate via
+|ssam_client_link|). It is important to do this, as it, first, guarantees
+that the returned controller is valid for use in the client driver for as
+long as this driver is bound to its device, i.e. that the driver gets
+unbound before the controller ever becomes invalid, and, second, as it
+ensures correct suspend/resume ordering. This setup should be done in the
+driver's probe function, and may be used to defer probing in case the SSAM
+subsystem is not ready yet, for example:
+
+.. code-block:: c
+
+   static int client_driver_probe(struct platform_device *pdev)
+   {
+           struct ssam_controller *ctrl;
+
+           ctrl = ssam_client_bind(&pdev->dev);
+           if (IS_ERR(ctrl))
+                   return PTR_ERR(ctrl) == -ENODEV ? -EPROBE_DEFER : PTR_ERR(ctrl);
+
+           // ...
+
+           return 0;
+   }
+
+The controller may be separately obtained via |ssam_get_controller| and its
+lifetime be guaranteed via |ssam_controller_get| and |ssam_controller_put|.
+Note that none of these functions, however, guarantee that the controller
+will not be shut down or suspended. These functions essentially only operate
+on the reference, i.e. only guarantee a bare minimum of accessibility
+without any guarantees at all on practical operability.
+
+
+Adding SSAM Devices
+===================
+
+If a device does not already exist/is not already provided via conventional
+means, it should be provided as |ssam_device| via the SSAM client device
+hub. New devices can be added to this hub by entering their UID into the
+corresponding registry. SSAM devices can also be manually allocated via
+|ssam_device_alloc|, subsequently to which they have to be added via
+|ssam_device_add| and eventually removed via |ssam_device_remove|. By
+default, the parent of the device is set to the controller device provided
+for allocation, however this may be changed before the device is added. Note
+that, when changing the parent device, care must be taken to ensure that the
+controller lifetime and suspend/resume ordering guarantees, in the default
+setup provided through the parent-child relation, are preserved. If
+necessary, by use of |ssam_client_link| as is done for non-SSAM client
+drivers and described in more detail above.
+
+A client device must always be removed by the party which added the
+respective device before the controller shuts down. Such removal can be
+guaranteed by linking the driver providing the SSAM device to the controller
+via |ssam_client_link|, causing it to unbind before the controller driver
+unbinds. Client devices registered with the controller as parent are
+automatically removed when the controller shuts down, but this should not be
+relied upon, especially as this does not extend to client devices with a
+different parent.
+
+
+SSAM Client Drivers
+===================
+
+SSAM client device drivers are, in essence, no different than other device
+driver types. They are represented via |ssam_device_driver| and bind to a
+|ssam_device| via its UID (:c:type:`struct ssam_device.uid <ssam_device>`)
+member and the match table
+(:c:type:`struct ssam_device_driver.match_table <ssam_device_driver>`),
+which should be set when declaring the driver struct instance. Refer to the
+|SSAM_DEVICE| macro documentation for more details on how to define members
+of the driver's match table.
+
+The UID for SSAM client devices consists of a ``domain``, a ``category``,
+a ``target``, an ``instance``, and a ``function``. The ``domain`` is used
+differentiate between physical SAM devices
+(:c:type:`SSAM_DOMAIN_SERIALHUB <ssam_device_domain>`), i.e. devices that can
+be accessed via the Surface Serial Hub, and virtual ones
+(:c:type:`SSAM_DOMAIN_VIRTUAL <ssam_device_domain>`), such as client-device
+hubs, that have no real representation on the SAM EC and are solely used on
+the kernel/driver-side. For physical devices, ``category`` represents the
+target category, ``target`` the target ID, and ``instance`` the instance ID
+used to access the physical SAM device. In addition, ``function`` references
+a specific device functionality, but has no meaning to the SAM EC. The
+(default) name of a client device is generated based on its UID.
+
+A driver instance can be registered via |ssam_device_driver_register| and
+unregistered via |ssam_device_driver_unregister|. For convenience, the
+|module_ssam_device_driver| macro may be used to define module init- and
+exit-functions registering the driver.
+
+The controller associated with a SSAM client device can be found in its
+:c:type:`struct ssam_device.ctrl <ssam_device>` member. This reference is
+guaranteed to be valid for at least as long as the client driver is bound,
+but should also be valid for as long as the client device exists. Note,
+however, that access outside of the bound client driver must ensure that the
+controller device is not suspended while making any requests or
+(un-)registering event notifiers (and thus should generally be avoided). This
+is guaranteed when the controller is accessed from inside the bound client
+driver.
+
+
+Making Synchronous Requests
+===========================
+
+Synchronous requests are (currently) the main form of host-initiated
+communication with the EC. There are a couple of ways to define and execute
+such requests, however, most of them boil down to something similar as shown
+in the example below. This example defines a write-read request, meaning
+that the caller provides an argument to the SAM EC and receives a response.
+The caller needs to know the (maximum) length of the response payload and
+provide a buffer for it.
+
+Care must be taken to ensure that any command payload data passed to the SAM
+EC is provided in little-endian format and, similarly, any response payload
+data received from it is converted from little-endian to host endianness.
+
+.. code-block:: c
+
+   int perform_request(struct ssam_controller *ctrl, u32 arg, u32 *ret)
+   {
+           struct ssam_request rqst;
+           struct ssam_response resp;
+           int status;
+
+           /* Convert request argument to little-endian. */
+           __le32 arg_le = cpu_to_le32(arg);
+           __le32 ret_le = cpu_to_le32(0);
+
+           /*
+            * Initialize request specification. Replace this with your values.
+            * The rqst.payload field may be NULL if rqst.length is zero,
+            * indicating that the request does not have any argument.
+            *
+            * Note: The request parameters used here are not valid, i.e.
+            *       they do not correspond to an actual SAM/EC request.
+            */
+           rqst.target_category = SSAM_SSH_TC_SAM;
+           rqst.target_id = 0x01;
+           rqst.command_id = 0x02;
+           rqst.instance_id = 0x03;
+           rqst.flags = SSAM_REQUEST_HAS_RESPONSE;
+           rqst.length = sizeof(arg_le);
+           rqst.payload = (u8 *)&arg_le;
+
+           /* Initialize request response. */
+           resp.capacity = sizeof(ret_le);
+           resp.length = 0;
+           resp.pointer = (u8 *)&ret_le;
+
+           /*
+            * Perform actual request. The response pointer may be null in case
+            * the request does not have any response. This must be consistent
+            * with the SSAM_REQUEST_HAS_RESPONSE flag set in the specification
+            * above.
+            */
+           status = ssam_request_sync(ctrl, &rqst, &resp);
+
+           /*
+            * Alternatively use
+            *
+            *   ssam_request_sync_onstack(ctrl, &rqst, &resp, sizeof(arg_le));
+            *
+            * to perform the request, allocating the message buffer directly
+            * on the stack as opposed to allocation via kzalloc().
+            */
+
+           /*
+            * Convert request response back to native format. Note that in the
+            * error case, this value is not touched by the SSAM core, i.e.
+            * 'ret_le' will be zero as specified in its initialization.
+            */
+           *ret = le32_to_cpu(ret_le);
+
+           return status;
+   }
+
+Note that |ssam_request_sync| in its essence is a wrapper over lower-level
+request primitives, which may also be used to perform requests. Refer to its
+implementation and documentation for more details.
+
+An arguably more user-friendly way of defining such functions is by using
+one of the generator macros, for example via:
+
+.. code-block:: c
+
+   SSAM_DEFINE_SYNC_REQUEST_W(__ssam_tmp_perf_mode_set, __le32, {
+           .target_category = SSAM_SSH_TC_TMP,
+           .target_id       = 0x01,
+           .command_id      = 0x03,
+           .instance_id     = 0x00,
+   });
+
+This example defines a function
+
+.. code-block:: c
+
+   static int __ssam_tmp_perf_mode_set(struct ssam_controller *ctrl, const __le32 *arg);
+
+executing the specified request, with the controller passed in when calling
+said function. In this example, the argument is provided via the ``arg``
+pointer. Note that the generated function allocates the message buffer on
+the stack. Thus, if the argument provided via the request is large, these
+kinds of macros should be avoided. Also note that, in contrast to the
+previous non-macro example, this function does not do any endianness
+conversion, which has to be handled by the caller. Apart from those
+differences the function generated by the macro is similar to the one
+provided in the non-macro example above.
+
+The full list of such function-generating macros is
+
+- :c:func:`SSAM_DEFINE_SYNC_REQUEST_N` for requests without return value and
+  without argument.
+- :c:func:`SSAM_DEFINE_SYNC_REQUEST_R` for requests with return value but no
+  argument.
+- :c:func:`SSAM_DEFINE_SYNC_REQUEST_W` for requests without return value but
+  with argument.
+
+Refer to their respective documentation for more details. For each one of
+these macros, a special variant is provided, which targets request types
+applicable to multiple instances of the same device type:
+
+- :c:func:`SSAM_DEFINE_SYNC_REQUEST_MD_N`
+- :c:func:`SSAM_DEFINE_SYNC_REQUEST_MD_R`
+- :c:func:`SSAM_DEFINE_SYNC_REQUEST_MD_W`
+
+The difference of those macros to the previously mentioned versions is, that
+the device target and instance IDs are not fixed for the generated function,
+but instead have to be provided by the caller of said function.
+
+Additionally, variants for direct use with client devices, i.e.
+|ssam_device|, are also provided. These can, for example, be used as
+follows:
+
+.. code-block:: c
+
+   SSAM_DEFINE_SYNC_REQUEST_CL_R(ssam_bat_get_sta, __le32, {
+           .target_category = SSAM_SSH_TC_BAT,
+           .command_id      = 0x01,
+   });
+
+This invocation of the macro defines a function
+
+.. code-block:: c
+
+   static int ssam_bat_get_sta(struct ssam_device *sdev, __le32 *ret);
+
+executing the specified request, using the device IDs and controller given
+in the client device. The full list of such macros for client devices is:
+
+- :c:func:`SSAM_DEFINE_SYNC_REQUEST_CL_N`
+- :c:func:`SSAM_DEFINE_SYNC_REQUEST_CL_R`
+- :c:func:`SSAM_DEFINE_SYNC_REQUEST_CL_W`
+
+
+Handling Events
+===============
+
+To receive events from the SAM EC, an event notifier must be registered for
+the desired event via |ssam_notifier_register|. The notifier must be
+unregistered via |ssam_notifier_unregister| once it is not required any
+more. For |ssam_device| type clients, the |ssam_device_notifier_register| and
+|ssam_device_notifier_unregister| wrappers should be preferred as they properly
+handle hot-removal of client devices.
+
+Event notifiers are registered by providing (at minimum) a callback to call
+in case an event has been received, the registry specifying how the event
+should be enabled, an event ID specifying for which target category and,
+optionally and depending on the registry used, for which instance ID events
+should be enabled, and finally, flags describing how the EC will send these
+events. If the specific registry does not enable events by instance ID, the
+instance ID must be set to zero. Additionally, a priority for the respective
+notifier may be specified, which determines its order in relation to any
+other notifier registered for the same target category.
+
+By default, event notifiers will receive all events for the specific target
+category, regardless of the instance ID specified when registering the
+notifier. The core may be instructed to only call a notifier if the target
+ID or instance ID (or both) of the event match the ones implied by the
+notifier IDs (in case of target ID, the target ID of the registry), by
+providing an event mask (see |ssam_event_mask|).
+
+In general, the target ID of the registry is also the target ID of the
+enabled event (with the notable exception being keyboard input events on the
+Surface Laptop 1 and 2, which are enabled via a registry with target ID 1,
+but provide events with target ID 2).
+
+A full example for registering an event notifier and handling received
+events is provided below:
+
+.. code-block:: c
+
+   u32 notifier_callback(struct ssam_event_notifier *nf,
+                         const struct ssam_event *event)
+   {
+           int status = ...
+
+           /* Handle the event here ... */
+
+           /* Convert return value and indicate that we handled the event. */
+           return ssam_notifier_from_errno(status) | SSAM_NOTIF_HANDLED;
+   }
+
+   int setup_notifier(struct ssam_device *sdev,
+                      struct ssam_event_notifier *nf)
+   {
+           /* Set priority wrt. other handlers of same target category. */
+           nf->base.priority = 1;
+
+           /* Set event/notifier callback. */
+           nf->base.fn = notifier_callback;
+
+           /* Specify event registry, i.e. how events get enabled/disabled. */
+           nf->event.reg = SSAM_EVENT_REGISTRY_KIP;
+
+           /* Specify which event to enable/disable */
+           nf->event.id.target_category = sdev->uid.category;
+           nf->event.id.instance = sdev->uid.instance;
+
+           /*
+            * Specify for which events the notifier callback gets executed.
+            * This essentially tells the core if it can skip notifiers that
+            * don't have target or instance IDs matching those of the event.
+            */
+           nf->event.mask = SSAM_EVENT_MASK_STRICT;
+
+           /* Specify event flags. */
+           nf->event.flags = SSAM_EVENT_SEQUENCED;
+
+           return ssam_notifier_register(sdev->ctrl, nf);
+   }
+
+Multiple event notifiers can be registered for the same event. The event
+handler core takes care of enabling and disabling events when notifiers are
+registered and unregistered, by keeping track of how many notifiers for a
+specific event (combination of registry, event target category, and event
+instance ID) are currently registered. This means that a specific event will
+be enabled when the first notifier for it is being registered and disabled
+when the last notifier for it is being unregistered. Note that the event
+flags are therefore only used on the first registered notifier, however, one
+should take care that notifiers for a specific event are always registered
+with the same flag and it is considered a bug to do otherwise.