Adding upstream version 6.1.76.upstream/6.1.76

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

1 files changed, 1712 insertions, 0 deletions

diff --git a/drivers/firmware/arm_scmi/notify.c b/drivers/firmware/arm_scmi/notify.c
new file mode 100644
index 000000000..0efd20cd9
--- /dev/null
+++ b/drivers/firmware/arm_scmi/notify.c
@@ -0,0 +1,1712 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * System Control and Management Interface (SCMI) Notification support
+ *
+ * Copyright (C) 2020-2021 ARM Ltd.
+ */
+/**
+ * DOC: Theory of operation
+ *
+ * SCMI Protocol specification allows the platform to signal events to
+ * interested agents via notification messages: this is an implementation
+ * of the dispatch and delivery of such notifications to the interested users
+ * inside the Linux kernel.
+ *
+ * An SCMI Notification core instance is initialized for each active platform
+ * instance identified by the means of the usual &struct scmi_handle.
+ *
+ * Each SCMI Protocol implementation, during its initialization, registers with
+ * this core its set of supported events using scmi_register_protocol_events():
+ * all the needed descriptors are stored in the &struct registered_protocols and
+ * &struct registered_events arrays.
+ *
+ * Kernel users interested in some specific event can register their callbacks
+ * providing the usual notifier_block descriptor, since this core implements
+ * events' delivery using the standard Kernel notification chains machinery.
+ *
+ * Given the number of possible events defined by SCMI and the extensibility
+ * of the SCMI Protocol itself, the underlying notification chains are created
+ * and destroyed dynamically on demand depending on the number of users
+ * effectively registered for an event, so that no support structures or chains
+ * are allocated until at least one user has registered a notifier_block for
+ * such event. Similarly, events' generation itself is enabled at the platform
+ * level only after at least one user has registered, and it is shutdown after
+ * the last user for that event has gone.
+ *
+ * All users provided callbacks and allocated notification-chains are stored in
+ * the @registered_events_handlers hashtable. Callbacks' registration requests
+ * for still to be registered events are instead kept in the dedicated common
+ * hashtable @pending_events_handlers.
+ *
+ * An event is identified univocally by the tuple (proto_id, evt_id, src_id)
+ * and is served by its own dedicated notification chain; information contained
+ * in such tuples is used, in a few different ways, to generate the needed
+ * hash-keys.
+ *
+ * Here proto_id and evt_id are simply the protocol_id and message_id numbers
+ * as described in the SCMI Protocol specification, while src_id represents an
+ * optional, protocol dependent, source identifier (like domain_id, perf_id
+ * or sensor_id and so forth).
+ *
+ * Upon reception of a notification message from the platform the SCMI RX ISR
+ * passes the received message payload and some ancillary information (including
+ * an arrival timestamp in nanoseconds) to the core via @scmi_notify() which
+ * pushes the event-data itself on a protocol-dedicated kfifo queue for further
+ * deferred processing as specified in @scmi_events_dispatcher().
+ *
+ * Each protocol has it own dedicated work_struct and worker which, once kicked
+ * by the ISR, takes care to empty its own dedicated queue, deliverying the
+ * queued items into the proper notification-chain: notifications processing can
+ * proceed concurrently on distinct workers only between events belonging to
+ * different protocols while delivery of events within the same protocol is
+ * still strictly sequentially ordered by time of arrival.
+ *
+ * Events' information is then extracted from the SCMI Notification messages and
+ * conveyed, converted into a custom per-event report struct, as the void *data
+ * param to the user callback provided by the registered notifier_block, so that
+ * from the user perspective his callback will look invoked like:
+ *
+ * int user_cb(struct notifier_block *nb, unsigned long event_id, void *report)
+ *
+ */
+
+#define dev_fmt(fmt) "SCMI Notifications - " fmt
+#define pr_fmt(fmt) "SCMI Notifications - " fmt
+
+#include <linux/bitfield.h>
+#include <linux/bug.h>
+#include <linux/compiler.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/hashtable.h>
+#include <linux/kernel.h>
+#include <linux/ktime.h>
+#include <linux/kfifo.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/notifier.h>
+#include <linux/refcount.h>
+#include <linux/scmi_protocol.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/workqueue.h>
+
+#include "common.h"
+#include "notify.h"
+
+#define SCMI_MAX_PROTO		256
+
+#define PROTO_ID_MASK		GENMASK(31, 24)
+#define EVT_ID_MASK		GENMASK(23, 16)
+#define SRC_ID_MASK		GENMASK(15, 0)
+
+/*
+ * Builds an unsigned 32bit key from the given input tuple to be used
+ * as a key in hashtables.
+ */
+#define MAKE_HASH_KEY(p, e, s)			\
+	(FIELD_PREP(PROTO_ID_MASK, (p)) |	\
+	   FIELD_PREP(EVT_ID_MASK, (e)) |	\
+	   FIELD_PREP(SRC_ID_MASK, (s)))
+
+#define MAKE_ALL_SRCS_KEY(p, e)		MAKE_HASH_KEY((p), (e), SRC_ID_MASK)
+
+/*
+ * Assumes that the stored obj includes its own hash-key in a field named 'key':
+ * with this simplification this macro can be equally used for all the objects'
+ * types hashed by this implementation.
+ *
+ * @__ht: The hashtable name
+ * @__obj: A pointer to the object type to be retrieved from the hashtable;
+ *	   it will be used as a cursor while scanning the hastable and it will
+ *	   be possibly left as NULL when @__k is not found
+ * @__k: The key to search for
+ */
+#define KEY_FIND(__ht, __obj, __k)				\
+({								\
+	typeof(__k) k_ = __k;					\
+	typeof(__obj) obj_;					\
+								\
+	hash_for_each_possible((__ht), obj_, hash, k_)		\
+		if (obj_->key == k_)				\
+			break;					\
+	__obj = obj_;						\
+})
+
+#define KEY_XTRACT_PROTO_ID(key)	FIELD_GET(PROTO_ID_MASK, (key))
+#define KEY_XTRACT_EVT_ID(key)		FIELD_GET(EVT_ID_MASK, (key))
+#define KEY_XTRACT_SRC_ID(key)		FIELD_GET(SRC_ID_MASK, (key))
+
+/*
+ * A set of macros used to access safely @registered_protocols and
+ * @registered_events arrays; these are fixed in size and each entry is possibly
+ * populated at protocols' registration time and then only read but NEVER
+ * modified or removed.
+ */
+#define SCMI_GET_PROTO(__ni, __pid)					\
+({									\
+	typeof(__ni) ni_ = __ni;					\
+	struct scmi_registered_events_desc *__pd = NULL;		\
+									\
+	if (ni_)							\
+		__pd = READ_ONCE(ni_->registered_protocols[(__pid)]);	\
+	__pd;								\
+})
+
+#define SCMI_GET_REVT_FROM_PD(__pd, __eid)				\
+({									\
+	typeof(__pd) pd_ = __pd;					\
+	typeof(__eid) eid_ = __eid;					\
+	struct scmi_registered_event *__revt = NULL;			\
+									\
+	if (pd_ && eid_ < pd_->num_events)				\
+		__revt = READ_ONCE(pd_->registered_events[eid_]);	\
+	__revt;								\
+})
+
+#define SCMI_GET_REVT(__ni, __pid, __eid)				\
+({									\
+	struct scmi_registered_event *__revt;				\
+	struct scmi_registered_events_desc *__pd;			\
+									\
+	__pd = SCMI_GET_PROTO((__ni), (__pid));				\
+	__revt = SCMI_GET_REVT_FROM_PD(__pd, (__eid));			\
+	__revt;								\
+})
+
+/* A couple of utility macros to limit cruft when calling protocols' helpers */
+#define REVT_NOTIFY_SET_STATUS(revt, eid, sid, state)		\
+({								\
+	typeof(revt) r = revt;					\
+	r->proto->ops->set_notify_enabled(r->proto->ph,		\
+					(eid), (sid), (state));	\
+})
+
+#define REVT_NOTIFY_ENABLE(revt, eid, sid)			\
+	REVT_NOTIFY_SET_STATUS((revt), (eid), (sid), true)
+
+#define REVT_NOTIFY_DISABLE(revt, eid, sid)			\
+	REVT_NOTIFY_SET_STATUS((revt), (eid), (sid), false)
+
+#define REVT_FILL_REPORT(revt, ...)				\
+({								\
+	typeof(revt) r = revt;					\
+	r->proto->ops->fill_custom_report(r->proto->ph,		\
+					  __VA_ARGS__);		\
+})
+
+#define SCMI_PENDING_HASH_SZ		4
+#define SCMI_REGISTERED_HASH_SZ		6
+
+struct scmi_registered_events_desc;
+
+/**
+ * struct scmi_notify_instance  - Represents an instance of the notification
+ * core
+ * @gid: GroupID used for devres
+ * @handle: A reference to the platform instance
+ * @init_work: A work item to perform final initializations of pending handlers
+ * @notify_wq: A reference to the allocated Kernel cmwq
+ * @pending_mtx: A mutex to protect @pending_events_handlers
+ * @registered_protocols: A statically allocated array containing pointers to
+ *			  all the registered protocol-level specific information
+ *			  related to events' handling
+ * @pending_events_handlers: An hashtable containing all pending events'
+ *			     handlers descriptors
+ *
+ * Each platform instance, represented by a handle, has its own instance of
+ * the notification subsystem represented by this structure.
+ */
+struct scmi_notify_instance {
+	void			*gid;
+	struct scmi_handle	*handle;
+	struct work_struct	init_work;
+	struct workqueue_struct	*notify_wq;
+	/* lock to protect pending_events_handlers */
+	struct mutex		pending_mtx;
+	struct scmi_registered_events_desc	**registered_protocols;
+	DECLARE_HASHTABLE(pending_events_handlers, SCMI_PENDING_HASH_SZ);
+};
+
+/**
+ * struct events_queue  - Describes a queue and its associated worker
+ * @sz: Size in bytes of the related kfifo
+ * @kfifo: A dedicated Kernel kfifo descriptor
+ * @notify_work: A custom work item bound to this queue
+ * @wq: A reference to the associated workqueue
+ *
+ * Each protocol has its own dedicated events_queue descriptor.
+ */
+struct events_queue {
+	size_t			sz;
+	struct kfifo		kfifo;
+	struct work_struct	notify_work;
+	struct workqueue_struct	*wq;
+};
+
+/**
+ * struct scmi_event_header  - A utility header
+ * @timestamp: The timestamp, in nanoseconds (boottime), which was associated
+ *	       to this event as soon as it entered the SCMI RX ISR
+ * @payld_sz: Effective size of the embedded message payload which follows
+ * @evt_id: Event ID (corresponds to the Event MsgID for this Protocol)
+ * @payld: A reference to the embedded event payload
+ *
+ * This header is prepended to each received event message payload before
+ * queueing it on the related &struct events_queue.
+ */
+struct scmi_event_header {
+	ktime_t timestamp;
+	size_t payld_sz;
+	unsigned char evt_id;
+	unsigned char payld[];
+};
+
+struct scmi_registered_event;
+
+/**
+ * struct scmi_registered_events_desc  - Protocol Specific information
+ * @id: Protocol ID
+ * @ops: Protocol specific and event-related operations
+ * @equeue: The embedded per-protocol events_queue
+ * @ni: A reference to the initialized instance descriptor
+ * @eh: A reference to pre-allocated buffer to be used as a scratch area by the
+ *	deferred worker when fetching data from the kfifo
+ * @eh_sz: Size of the pre-allocated buffer @eh
+ * @in_flight: A reference to an in flight &struct scmi_registered_event
+ * @num_events: Number of events in @registered_events
+ * @registered_events: A dynamically allocated array holding all the registered
+ *		       events' descriptors, whose fixed-size is determined at
+ *		       compile time.
+ * @registered_mtx: A mutex to protect @registered_events_handlers
+ * @ph: SCMI protocol handle reference
+ * @registered_events_handlers: An hashtable containing all events' handlers
+ *				descriptors registered for this protocol
+ *
+ * All protocols that register at least one event have their protocol-specific
+ * information stored here, together with the embedded allocated events_queue.
+ * These descriptors are stored in the @registered_protocols array at protocol
+ * registration time.
+ *
+ * Once these descriptors are successfully registered, they are NEVER again
+ * removed or modified since protocols do not unregister ever, so that, once
+ * we safely grab a NON-NULL reference from the array we can keep it and use it.
+ */
+struct scmi_registered_events_desc {
+	u8				id;
+	const struct scmi_event_ops	*ops;
+	struct events_queue		equeue;
+	struct scmi_notify_instance	*ni;
+	struct scmi_event_header	*eh;
+	size_t				eh_sz;
+	void				*in_flight;
+	int				num_events;
+	struct scmi_registered_event	**registered_events;
+	/* mutex to protect registered_events_handlers */
+	struct mutex			registered_mtx;
+	const struct scmi_protocol_handle	*ph;
+	DECLARE_HASHTABLE(registered_events_handlers, SCMI_REGISTERED_HASH_SZ);
+};
+
+/**
+ * struct scmi_registered_event  - Event Specific Information
+ * @proto: A reference to the associated protocol descriptor
+ * @evt: A reference to the associated event descriptor (as provided at
+ *       registration time)
+ * @report: A pre-allocated buffer used by the deferred worker to fill a
+ *	    customized event report
+ * @num_sources: The number of possible sources for this event as stated at
+ *		 events' registration time
+ * @sources: A reference to a dynamically allocated array used to refcount the
+ *	     events' enable requests for all the existing sources
+ * @sources_mtx: A mutex to serialize the access to @sources
+ *
+ * All registered events are represented by one of these structures that are
+ * stored in the @registered_events array at protocol registration time.
+ *
+ * Once these descriptors are successfully registered, they are NEVER again
+ * removed or modified since protocols do not unregister ever, so that once we
+ * safely grab a NON-NULL reference from the table we can keep it and use it.
+ */
+struct scmi_registered_event {
+	struct scmi_registered_events_desc *proto;
+	const struct scmi_event	*evt;
+	void		*report;
+	u32		num_sources;
+	refcount_t	*sources;
+	/* locking to serialize the access to sources */
+	struct mutex	sources_mtx;
+};
+
+/**
+ * struct scmi_event_handler  - Event handler information
+ * @key: The used hashkey
+ * @users: A reference count for number of active users for this handler
+ * @r_evt: A reference to the associated registered event; when this is NULL
+ *	   this handler is pending, which means that identifies a set of
+ *	   callbacks intended to be attached to an event which is still not
+ *	   known nor registered by any protocol at that point in time
+ * @chain: The notification chain dedicated to this specific event tuple
+ * @hash: The hlist_node used for collision handling
+ * @enabled: A boolean which records if event's generation has been already
+ *	     enabled for this handler as a whole
+ *
+ * This structure collects all the information needed to process a received
+ * event identified by the tuple (proto_id, evt_id, src_id).
+ * These descriptors are stored in a per-protocol @registered_events_handlers
+ * table using as a key a value derived from that tuple.
+ */
+struct scmi_event_handler {
+	u32				key;
+	refcount_t			users;
+	struct scmi_registered_event	*r_evt;
+	struct blocking_notifier_head	chain;
+	struct hlist_node		hash;
+	bool				enabled;
+};
+
+#define IS_HNDL_PENDING(hndl)	(!(hndl)->r_evt)
+
+static struct scmi_event_handler *
+scmi_get_active_handler(struct scmi_notify_instance *ni, u32 evt_key);
+static void scmi_put_active_handler(struct scmi_notify_instance *ni,
+				    struct scmi_event_handler *hndl);
+static bool scmi_put_handler_unlocked(struct scmi_notify_instance *ni,
+				      struct scmi_event_handler *hndl);
+
+/**
+ * scmi_lookup_and_call_event_chain()  - Lookup the proper chain and call it
+ * @ni: A reference to the notification instance to use
+ * @evt_key: The key to use to lookup the related notification chain
+ * @report: The customized event-specific report to pass down to the callbacks
+ *	    as their *data parameter.
+ */
+static inline void
+scmi_lookup_and_call_event_chain(struct scmi_notify_instance *ni,
+				 u32 evt_key, void *report)
+{
+	int ret;
+	struct scmi_event_handler *hndl;
+
+	/*
+	 * Here ensure the event handler cannot vanish while using it.
+	 * It is legitimate, though, for an handler not to be found at all here,
+	 * e.g. when it has been unregistered by the user after some events had
+	 * already been queued.
+	 */
+	hndl = scmi_get_active_handler(ni, evt_key);
+	if (!hndl)
+		return;
+
+	ret = blocking_notifier_call_chain(&hndl->chain,
+					   KEY_XTRACT_EVT_ID(evt_key),
+					   report);
+	/* Notifiers are NOT supposed to cut the chain ... */
+	WARN_ON_ONCE(ret & NOTIFY_STOP_MASK);
+
+	scmi_put_active_handler(ni, hndl);
+}
+
+/**
+ * scmi_process_event_header()  - Dequeue and process an event header
+ * @eq: The queue to use
+ * @pd: The protocol descriptor to use
+ *
+ * Read an event header from the protocol queue into the dedicated scratch
+ * buffer and looks for a matching registered event; in case an anomalously
+ * sized read is detected just flush the queue.
+ *
+ * Return:
+ * * a reference to the matching registered event when found
+ * * ERR_PTR(-EINVAL) when NO registered event could be found
+ * * NULL when the queue is empty
+ */
+static inline struct scmi_registered_event *
+scmi_process_event_header(struct events_queue *eq,
+			  struct scmi_registered_events_desc *pd)
+{
+	unsigned int outs;
+	struct scmi_registered_event *r_evt;
+
+	outs = kfifo_out(&eq->kfifo, pd->eh,
+			 sizeof(struct scmi_event_header));
+	if (!outs)
+		return NULL;
+	if (outs != sizeof(struct scmi_event_header)) {
+		dev_err(pd->ni->handle->dev, "corrupted EVT header. Flush.\n");
+		kfifo_reset_out(&eq->kfifo);
+		return NULL;
+	}
+
+	r_evt = SCMI_GET_REVT_FROM_PD(pd, pd->eh->evt_id);
+	if (!r_evt)
+		r_evt = ERR_PTR(-EINVAL);
+
+	return r_evt;
+}
+
+/**
+ * scmi_process_event_payload()  - Dequeue and process an event payload
+ * @eq: The queue to use
+ * @pd: The protocol descriptor to use
+ * @r_evt: The registered event descriptor to use
+ *
+ * Read an event payload from the protocol queue into the dedicated scratch
+ * buffer, fills a custom report and then look for matching event handlers and
+ * call them; skip any unknown event (as marked by scmi_process_event_header())
+ * and in case an anomalously sized read is detected just flush the queue.
+ *
+ * Return: False when the queue is empty
+ */
+static inline bool
+scmi_process_event_payload(struct events_queue *eq,
+			   struct scmi_registered_events_desc *pd,
+			   struct scmi_registered_event *r_evt)
+{
+	u32 src_id, key;
+	unsigned int outs;
+	void *report = NULL;
+
+	outs = kfifo_out(&eq->kfifo, pd->eh->payld, pd->eh->payld_sz);
+	if (!outs)
+		return false;
+
+	/* Any in-flight event has now been officially processed */
+	pd->in_flight = NULL;
+
+	if (outs != pd->eh->payld_sz) {
+		dev_err(pd->ni->handle->dev, "corrupted EVT Payload. Flush.\n");
+		kfifo_reset_out(&eq->kfifo);
+		return false;
+	}
+
+	if (IS_ERR(r_evt)) {
+		dev_warn(pd->ni->handle->dev,
+			 "SKIP UNKNOWN EVT - proto:%X  evt:%d\n",
+			 pd->id, pd->eh->evt_id);
+		return true;
+	}
+
+	report = REVT_FILL_REPORT(r_evt, pd->eh->evt_id, pd->eh->timestamp,
+				  pd->eh->payld, pd->eh->payld_sz,
+				  r_evt->report, &src_id);
+	if (!report) {
+		dev_err(pd->ni->handle->dev,
+			"report not available - proto:%X  evt:%d\n",
+			pd->id, pd->eh->evt_id);
+		return true;
+	}
+
+	/* At first search for a generic ALL src_ids handler... */
+	key = MAKE_ALL_SRCS_KEY(pd->id, pd->eh->evt_id);
+	scmi_lookup_and_call_event_chain(pd->ni, key, report);
+
+	/* ...then search for any specific src_id */
+	key = MAKE_HASH_KEY(pd->id, pd->eh->evt_id, src_id);
+	scmi_lookup_and_call_event_chain(pd->ni, key, report);
+
+	return true;
+}
+
+/**
+ * scmi_events_dispatcher()  - Common worker logic for all work items.
+ * @work: The work item to use, which is associated to a dedicated events_queue
+ *
+ * Logic:
+ *  1. dequeue one pending RX notification (queued in SCMI RX ISR context)
+ *  2. generate a custom event report from the received event message
+ *  3. lookup for any registered ALL_SRC_IDs handler:
+ *    - > call the related notification chain passing in the report
+ *  4. lookup for any registered specific SRC_ID handler:
+ *    - > call the related notification chain passing in the report
+ *
+ * Note that:
+ * * a dedicated per-protocol kfifo queue is used: in this way an anomalous
+ *   flood of events cannot saturate other protocols' queues.
+ * * each per-protocol queue is associated to a distinct work_item, which
+ *   means, in turn, that:
+ *   + all protocols can process their dedicated queues concurrently
+ *     (since notify_wq:max_active != 1)
+ *   + anyway at most one worker instance is allowed to run on the same queue
+ *     concurrently: this ensures that we can have only one concurrent
+ *     reader/writer on the associated kfifo, so that we can use it lock-less
+ *
+ * Context: Process context.
+ */
+static void scmi_events_dispatcher(struct work_struct *work)
+{
+	struct events_queue *eq;
+	struct scmi_registered_events_desc *pd;
+	struct scmi_registered_event *r_evt;
+
+	eq = container_of(work, struct events_queue, notify_work);
+	pd = container_of(eq, struct scmi_registered_events_desc, equeue);
+	/*
+	 * In order to keep the queue lock-less and the number of memcopies
+	 * to the bare minimum needed, the dispatcher accounts for the
+	 * possibility of per-protocol in-flight events: i.e. an event whose
+	 * reception could end up being split across two subsequent runs of this
+	 * worker, first the header, then the payload.
+	 */
+	do {
+		if (!pd->in_flight) {
+			r_evt = scmi_process_event_header(eq, pd);
+			if (!r_evt)
+				break;
+			pd->in_flight = r_evt;
+		} else {
+			r_evt = pd->in_flight;
+		}
+	} while (scmi_process_event_payload(eq, pd, r_evt));
+}
+
+/**
+ * scmi_notify()  - Queues a notification for further deferred processing
+ * @handle: The handle identifying the platform instance from which the
+ *	    dispatched event is generated
+ * @proto_id: Protocol ID
+ * @evt_id: Event ID (msgID)
+ * @buf: Event Message Payload (without the header)
+ * @len: Event Message Payload size
+ * @ts: RX Timestamp in nanoseconds (boottime)
+ *
+ * Context: Called in interrupt context to queue a received event for
+ * deferred processing.
+ *
+ * Return: 0 on Success
+ */
+int scmi_notify(const struct scmi_handle *handle, u8 proto_id, u8 evt_id,
+		const void *buf, size_t len, ktime_t ts)
+{
+	struct scmi_registered_event *r_evt;
+	struct scmi_event_header eh;
+	struct scmi_notify_instance *ni;
+
+	ni = scmi_notification_instance_data_get(handle);
+	if (!ni)
+		return 0;
+
+	r_evt = SCMI_GET_REVT(ni, proto_id, evt_id);
+	if (!r_evt)
+		return -EINVAL;
+
+	if (len > r_evt->evt->max_payld_sz) {
+		dev_err(handle->dev, "discard badly sized message\n");
+		return -EINVAL;
+	}
+	if (kfifo_avail(&r_evt->proto->equeue.kfifo) < sizeof(eh) + len) {
+		dev_warn(handle->dev,
+			 "queue full, dropping proto_id:%d  evt_id:%d  ts:%lld\n",
+			 proto_id, evt_id, ktime_to_ns(ts));
+		return -ENOMEM;
+	}
+
+	eh.timestamp = ts;
+	eh.evt_id = evt_id;
+	eh.payld_sz = len;
+	/*
+	 * Header and payload are enqueued with two distinct kfifo_in() (so non
+	 * atomic), but this situation is handled properly on the consumer side
+	 * with in-flight events tracking.
+	 */
+	kfifo_in(&r_evt->proto->equeue.kfifo, &eh, sizeof(eh));
+	kfifo_in(&r_evt->proto->equeue.kfifo, buf, len);
+	/*
+	 * Don't care about return value here since we just want to ensure that
+	 * a work is queued all the times whenever some items have been pushed
+	 * on the kfifo:
+	 * - if work was already queued it will simply fail to queue a new one
+	 *   since it is not needed
+	 * - if work was not queued already it will be now, even in case work
+	 *   was in fact already running: this behavior avoids any possible race
+	 *   when this function pushes new items onto the kfifos after the
+	 *   related executing worker had already determined the kfifo to be
+	 *   empty and it was terminating.
+	 */
+	queue_work(r_evt->proto->equeue.wq,
+		   &r_evt->proto->equeue.notify_work);
+
+	return 0;
+}
+
+/**
+ * scmi_kfifo_free()  - Devres action helper to free the kfifo
+ * @kfifo: The kfifo to free
+ */
+static void scmi_kfifo_free(void *kfifo)
+{
+	kfifo_free((struct kfifo *)kfifo);
+}
+
+/**
+ * scmi_initialize_events_queue()  - Allocate/Initialize a kfifo buffer
+ * @ni: A reference to the notification instance to use
+ * @equeue: The events_queue to initialize
+ * @sz: Size of the kfifo buffer to allocate
+ *
+ * Allocate a buffer for the kfifo and initialize it.
+ *
+ * Return: 0 on Success
+ */
+static int scmi_initialize_events_queue(struct scmi_notify_instance *ni,
+					struct events_queue *equeue, size_t sz)
+{
+	int ret;
+
+	if (kfifo_alloc(&equeue->kfifo, sz, GFP_KERNEL))
+		return -ENOMEM;
+	/* Size could have been roundup to power-of-two */
+	equeue->sz = kfifo_size(&equeue->kfifo);
+
+	ret = devm_add_action_or_reset(ni->handle->dev, scmi_kfifo_free,
+				       &equeue->kfifo);
+	if (ret)
+		return ret;
+
+	INIT_WORK(&equeue->notify_work, scmi_events_dispatcher);
+	equeue->wq = ni->notify_wq;
+
+	return ret;
+}
+
+/**
+ * scmi_allocate_registered_events_desc()  - Allocate a registered events'
+ * descriptor
+ * @ni: A reference to the &struct scmi_notify_instance notification instance
+ *	to use
+ * @proto_id: Protocol ID
+ * @queue_sz: Size of the associated queue to allocate
+ * @eh_sz: Size of the event header scratch area to pre-allocate
+ * @num_events: Number of events to support (size of @registered_events)
+ * @ops: Pointer to a struct holding references to protocol specific helpers
+ *	 needed during events handling
+ *
+ * It is supposed to be called only once for each protocol at protocol
+ * initialization time, so it warns if the requested protocol is found already
+ * registered.
+ *
+ * Return: The allocated and registered descriptor on Success
+ */
+static struct scmi_registered_events_desc *
+scmi_allocate_registered_events_desc(struct scmi_notify_instance *ni,
+				     u8 proto_id, size_t queue_sz, size_t eh_sz,
+				     int num_events,
+				     const struct scmi_event_ops *ops)
+{
+	int ret;
+	struct scmi_registered_events_desc *pd;
+
+	/* Ensure protocols are up to date */
+	smp_rmb();
+	if (WARN_ON(ni->registered_protocols[proto_id]))
+		return ERR_PTR(-EINVAL);
+
+	pd = devm_kzalloc(ni->handle->dev, sizeof(*pd), GFP_KERNEL);
+	if (!pd)
+		return ERR_PTR(-ENOMEM);
+	pd->id = proto_id;
+	pd->ops = ops;
+	pd->ni = ni;
+
+	ret = scmi_initialize_events_queue(ni, &pd->equeue, queue_sz);
+	if (ret)
+		return ERR_PTR(ret);
+
+	pd->eh = devm_kzalloc(ni->handle->dev, eh_sz, GFP_KERNEL);
+	if (!pd->eh)
+		return ERR_PTR(-ENOMEM);
+	pd->eh_sz = eh_sz;
+
+	pd->registered_events = devm_kcalloc(ni->handle->dev, num_events,
+					     sizeof(char *), GFP_KERNEL);
+	if (!pd->registered_events)
+		return ERR_PTR(-ENOMEM);
+	pd->num_events = num_events;
+
+	/* Initialize per protocol handlers table */
+	mutex_init(&pd->registered_mtx);
+	hash_init(pd->registered_events_handlers);
+
+	return pd;
+}
+
+/**
+ * scmi_register_protocol_events()  - Register Protocol Events with the core
+ * @handle: The handle identifying the platform instance against which the
+ *	    protocol's events are registered
+ * @proto_id: Protocol ID
+ * @ph: SCMI protocol handle.
+ * @ee: A structure describing the events supported by this protocol.
+ *
+ * Used by SCMI Protocols initialization code to register with the notification
+ * core the list of supported events and their descriptors: takes care to
+ * pre-allocate and store all needed descriptors, scratch buffers and event
+ * queues.
+ *
+ * Return: 0 on Success
+ */
+int scmi_register_protocol_events(const struct scmi_handle *handle, u8 proto_id,
+				  const struct scmi_protocol_handle *ph,
+				  const struct scmi_protocol_events *ee)
+{
+	int i;
+	unsigned int num_sources;
+	size_t payld_sz = 0;
+	struct scmi_registered_events_desc *pd;
+	struct scmi_notify_instance *ni;
+	const struct scmi_event *evt;
+
+	if (!ee || !ee->ops || !ee->evts || !ph ||
+	    (!ee->num_sources && !ee->ops->get_num_sources))
+		return -EINVAL;
+
+	ni = scmi_notification_instance_data_get(handle);
+	if (!ni)
+		return -ENOMEM;
+
+	/* num_sources cannot be <= 0 */
+	if (ee->num_sources) {
+		num_sources = ee->num_sources;
+	} else {
+		int nsrc = ee->ops->get_num_sources(ph);
+
+		if (nsrc <= 0)
+			return -EINVAL;
+		num_sources = nsrc;
+	}
+
+	evt = ee->evts;
+	for (i = 0; i < ee->num_events; i++)
+		payld_sz = max_t(size_t, payld_sz, evt[i].max_payld_sz);
+	payld_sz += sizeof(struct scmi_event_header);
+
+	pd = scmi_allocate_registered_events_desc(ni, proto_id, ee->queue_sz,
+						  payld_sz, ee->num_events,
+						  ee->ops);
+	if (IS_ERR(pd))
+		return PTR_ERR(pd);
+
+	pd->ph = ph;
+	for (i = 0; i < ee->num_events; i++, evt++) {
+		struct scmi_registered_event *r_evt;
+
+		r_evt = devm_kzalloc(ni->handle->dev, sizeof(*r_evt),
+				     GFP_KERNEL);
+		if (!r_evt)
+			return -ENOMEM;
+		r_evt->proto = pd;
+		r_evt->evt = evt;
+
+		r_evt->sources = devm_kcalloc(ni->handle->dev, num_sources,
+					      sizeof(refcount_t), GFP_KERNEL);
+		if (!r_evt->sources)
+			return -ENOMEM;
+		r_evt->num_sources = num_sources;
+		mutex_init(&r_evt->sources_mtx);
+
+		r_evt->report = devm_kzalloc(ni->handle->dev,
+					     evt->max_report_sz, GFP_KERNEL);
+		if (!r_evt->report)
+			return -ENOMEM;
+
+		pd->registered_events[i] = r_evt;
+		/* Ensure events are updated */
+		smp_wmb();
+		dev_dbg(handle->dev, "registered event - %lX\n",
+			MAKE_ALL_SRCS_KEY(r_evt->proto->id, r_evt->evt->id));
+	}
+
+	/* Register protocol and events...it will never be removed */
+	ni->registered_protocols[proto_id] = pd;
+	/* Ensure protocols are updated */
+	smp_wmb();
+
+	/*
+	 * Finalize any pending events' handler which could have been waiting
+	 * for this protocol's events registration.
+	 */
+	schedule_work(&ni->init_work);
+
+	return 0;
+}
+
+/**
+ * scmi_deregister_protocol_events  - Deregister protocol events with the core
+ * @handle: The handle identifying the platform instance against which the
+ *	    protocol's events are registered
+ * @proto_id: Protocol ID
+ */
+void scmi_deregister_protocol_events(const struct scmi_handle *handle,
+				     u8 proto_id)
+{
+	struct scmi_notify_instance *ni;
+	struct scmi_registered_events_desc *pd;
+
+	ni = scmi_notification_instance_data_get(handle);
+	if (!ni)
+		return;
+
+	pd = ni->registered_protocols[proto_id];
+	if (!pd)
+		return;
+
+	ni->registered_protocols[proto_id] = NULL;
+	/* Ensure protocols are updated */
+	smp_wmb();
+
+	cancel_work_sync(&pd->equeue.notify_work);
+}
+
+/**
+ * scmi_allocate_event_handler()  - Allocate Event handler
+ * @ni: A reference to the notification instance to use
+ * @evt_key: 32bit key uniquely bind to the event identified by the tuple
+ *	     (proto_id, evt_id, src_id)
+ *
+ * Allocate an event handler and related notification chain associated with
+ * the provided event handler key.
+ * Note that, at this point, a related registered_event is still to be
+ * associated to this handler descriptor (hndl->r_evt == NULL), so the handler
+ * is initialized as pending.
+ *
+ * Context: Assumes to be called with @pending_mtx already acquired.
+ * Return: the freshly allocated structure on Success
+ */
+static struct scmi_event_handler *
+scmi_allocate_event_handler(struct scmi_notify_instance *ni, u32 evt_key)
+{
+	struct scmi_event_handler *hndl;
+
+	hndl = kzalloc(sizeof(*hndl), GFP_KERNEL);
+	if (!hndl)
+		return NULL;
+	hndl->key = evt_key;
+	BLOCKING_INIT_NOTIFIER_HEAD(&hndl->chain);
+	refcount_set(&hndl->users, 1);
+	/* New handlers are created pending */
+	hash_add(ni->pending_events_handlers, &hndl->hash, hndl->key);
+
+	return hndl;
+}
+
+/**
+ * scmi_free_event_handler()  - Free the provided Event handler
+ * @hndl: The event handler structure to free
+ *
+ * Context: Assumes to be called with proper locking acquired depending
+ *	    on the situation.
+ */
+static void scmi_free_event_handler(struct scmi_event_handler *hndl)
+{
+	hash_del(&hndl->hash);
+	kfree(hndl);
+}
+
+/**
+ * scmi_bind_event_handler()  - Helper to attempt binding an handler to an event
+ * @ni: A reference to the notification instance to use
+ * @hndl: The event handler to bind
+ *
+ * If an associated registered event is found, move the handler from the pending
+ * into the registered table.
+ *
+ * Context: Assumes to be called with @pending_mtx already acquired.
+ *
+ * Return: 0 on Success
+ */
+static inline int scmi_bind_event_handler(struct scmi_notify_instance *ni,
+					  struct scmi_event_handler *hndl)
+{
+	struct scmi_registered_event *r_evt;
+
+	r_evt = SCMI_GET_REVT(ni, KEY_XTRACT_PROTO_ID(hndl->key),
+			      KEY_XTRACT_EVT_ID(hndl->key));
+	if (!r_evt)
+		return -EINVAL;
+
+	/*
+	 * Remove from pending and insert into registered while getting hold
+	 * of protocol instance.
+	 */
+	hash_del(&hndl->hash);
+	/*
+	 * Acquire protocols only for NON pending handlers, so as NOT to trigger
+	 * protocol initialization when a notifier is registered against a still
+	 * not registered protocol, since it would make little sense to force init
+	 * protocols for which still no SCMI driver user exists: they wouldn't
+	 * emit any event anyway till some SCMI driver starts using it.
+	 */
+	scmi_protocol_acquire(ni->handle, KEY_XTRACT_PROTO_ID(hndl->key));
+	hndl->r_evt = r_evt;
+
+	mutex_lock(&r_evt->proto->registered_mtx);
+	hash_add(r_evt->proto->registered_events_handlers,
+		 &hndl->hash, hndl->key);
+	mutex_unlock(&r_evt->proto->registered_mtx);
+
+	return 0;
+}
+
+/**
+ * scmi_valid_pending_handler()  - Helper to check pending status of handlers
+ * @ni: A reference to the notification instance to use
+ * @hndl: The event handler to check
+ *
+ * An handler is considered pending when its r_evt == NULL, because the related
+ * event was still unknown at handler's registration time; anyway, since all
+ * protocols register their supported events once for all at protocols'
+ * initialization time, a pending handler cannot be considered valid anymore if
+ * the underlying event (which it is waiting for), belongs to an already
+ * initialized and registered protocol.
+ *
+ * Return: 0 on Success
+ */
+static inline int scmi_valid_pending_handler(struct scmi_notify_instance *ni,
+					     struct scmi_event_handler *hndl)
+{
+	struct scmi_registered_events_desc *pd;
+
+	if (!IS_HNDL_PENDING(hndl))
+		return -EINVAL;
+
+	pd = SCMI_GET_PROTO(ni, KEY_XTRACT_PROTO_ID(hndl->key));
+	if (pd)
+		return -EINVAL;
+
+	return 0;
+}
+
+/**
+ * scmi_register_event_handler()  - Register whenever possible an Event handler
+ * @ni: A reference to the notification instance to use
+ * @hndl: The event handler to register
+ *
+ * At first try to bind an event handler to its associated event, then check if
+ * it was at least a valid pending handler: if it was not bound nor valid return
+ * false.
+ *
+ * Valid pending incomplete bindings will be periodically retried by a dedicated
+ * worker which is kicked each time a new protocol completes its own
+ * registration phase.
+ *
+ * Context: Assumes to be called with @pending_mtx acquired.
+ *
+ * Return: 0 on Success
+ */
+static int scmi_register_event_handler(struct scmi_notify_instance *ni,
+				       struct scmi_event_handler *hndl)
+{
+	int ret;
+
+	ret = scmi_bind_event_handler(ni, hndl);
+	if (!ret) {
+		dev_dbg(ni->handle->dev, "registered NEW handler - key:%X\n",
+			hndl->key);
+	} else {
+		ret = scmi_valid_pending_handler(ni, hndl);
+		if (!ret)
+			dev_dbg(ni->handle->dev,
+				"registered PENDING handler - key:%X\n",
+				hndl->key);
+	}
+
+	return ret;
+}
+
+/**
+ * __scmi_event_handler_get_ops()  - Utility to get or create an event handler
+ * @ni: A reference to the notification instance to use
+ * @evt_key: The event key to use
+ * @create: A boolean flag to specify if a handler must be created when
+ *	    not already existent
+ *
+ * Search for the desired handler matching the key in both the per-protocol
+ * registered table and the common pending table:
+ * * if found adjust users refcount
+ * * if not found and @create is true, create and register the new handler:
+ *   handler could end up being registered as pending if no matching event
+ *   could be found.
+ *
+ * An handler is guaranteed to reside in one and only one of the tables at
+ * any one time; to ensure this the whole search and create is performed
+ * holding the @pending_mtx lock, with @registered_mtx additionally acquired
+ * if needed.
+ *
+ * Note that when a nested acquisition of these mutexes is needed the locking
+ * order is always (same as in @init_work):
+ * 1. pending_mtx
+ * 2. registered_mtx
+ *
+ * Events generation is NOT enabled right after creation within this routine
+ * since at creation time we usually want to have all setup and ready before
+ * events really start flowing.
+ *
+ * Return: A properly refcounted handler on Success, NULL on Failure
+ */
+static inline struct scmi_event_handler *
+__scmi_event_handler_get_ops(struct scmi_notify_instance *ni,
+			     u32 evt_key, bool create)
+{
+	struct scmi_registered_event *r_evt;
+	struct scmi_event_handler *hndl = NULL;
+
+	r_evt = SCMI_GET_REVT(ni, KEY_XTRACT_PROTO_ID(evt_key),
+			      KEY_XTRACT_EVT_ID(evt_key));
+
+	mutex_lock(&ni->pending_mtx);
+	/* Search registered events at first ... if possible at all */
+	if (r_evt) {
+		mutex_lock(&r_evt->proto->registered_mtx);
+		hndl = KEY_FIND(r_evt->proto->registered_events_handlers,
+				hndl, evt_key);
+		if (hndl)
+			refcount_inc(&hndl->users);
+		mutex_unlock(&r_evt->proto->registered_mtx);
+	}
+
+	/* ...then amongst pending. */
+	if (!hndl) {
+		hndl = KEY_FIND(ni->pending_events_handlers, hndl, evt_key);
+		if (hndl)
+			refcount_inc(&hndl->users);
+	}
+
+	/* Create if still not found and required */
+	if (!hndl && create) {
+		hndl = scmi_allocate_event_handler(ni, evt_key);
+		if (hndl && scmi_register_event_handler(ni, hndl)) {
+			dev_dbg(ni->handle->dev,
+				"purging UNKNOWN handler - key:%X\n",
+				hndl->key);
+			/* this hndl can be only a pending one */
+			scmi_put_handler_unlocked(ni, hndl);
+			hndl = NULL;
+		}
+	}
+	mutex_unlock(&ni->pending_mtx);
+
+	return hndl;
+}
+
+static struct scmi_event_handler *
+scmi_get_handler(struct scmi_notify_instance *ni, u32 evt_key)
+{
+	return __scmi_event_handler_get_ops(ni, evt_key, false);
+}
+
+static struct scmi_event_handler *
+scmi_get_or_create_handler(struct scmi_notify_instance *ni, u32 evt_key)
+{
+	return __scmi_event_handler_get_ops(ni, evt_key, true);
+}
+
+/**
+ * scmi_get_active_handler()  - Helper to get active handlers only
+ * @ni: A reference to the notification instance to use
+ * @evt_key: The event key to use
+ *
+ * Search for the desired handler matching the key only in the per-protocol
+ * table of registered handlers: this is called only from the dispatching path
+ * so want to be as quick as possible and do not care about pending.
+ *
+ * Return: A properly refcounted active handler
+ */
+static struct scmi_event_handler *
+scmi_get_active_handler(struct scmi_notify_instance *ni, u32 evt_key)
+{
+	struct scmi_registered_event *r_evt;
+	struct scmi_event_handler *hndl = NULL;
+
+	r_evt = SCMI_GET_REVT(ni, KEY_XTRACT_PROTO_ID(evt_key),
+			      KEY_XTRACT_EVT_ID(evt_key));
+	if (r_evt) {
+		mutex_lock(&r_evt->proto->registered_mtx);
+		hndl = KEY_FIND(r_evt->proto->registered_events_handlers,
+				hndl, evt_key);
+		if (hndl)
+			refcount_inc(&hndl->users);
+		mutex_unlock(&r_evt->proto->registered_mtx);
+	}
+
+	return hndl;
+}
+
+/**
+ * __scmi_enable_evt()  - Enable/disable events generation
+ * @r_evt: The registered event to act upon
+ * @src_id: The src_id to act upon
+ * @enable: The action to perform: true->Enable, false->Disable
+ *
+ * Takes care of proper refcounting while performing enable/disable: handles
+ * the special case of ALL sources requests by itself.
+ * Returns successfully if at least one of the required src_id has been
+ * successfully enabled/disabled.
+ *
+ * Return: 0 on Success
+ */
+static inline int __scmi_enable_evt(struct scmi_registered_event *r_evt,
+				    u32 src_id, bool enable)
+{
+	int retvals = 0;
+	u32 num_sources;
+	refcount_t *sid;
+
+	if (src_id == SRC_ID_MASK) {
+		src_id = 0;
+		num_sources = r_evt->num_sources;
+	} else if (src_id < r_evt->num_sources) {
+		num_sources = 1;
+	} else {
+		return -EINVAL;
+	}
+
+	mutex_lock(&r_evt->sources_mtx);
+	if (enable) {
+		for (; num_sources; src_id++, num_sources--) {
+			int ret = 0;
+
+			sid = &r_evt->sources[src_id];
+			if (refcount_read(sid) == 0) {
+				ret = REVT_NOTIFY_ENABLE(r_evt, r_evt->evt->id,
+							 src_id);
+				if (!ret)
+					refcount_set(sid, 1);
+			} else {
+				refcount_inc(sid);
+			}
+			retvals += !ret;
+		}
+	} else {
+		for (; num_sources; src_id++, num_sources--) {
+			sid = &r_evt->sources[src_id];
+			if (refcount_dec_and_test(sid))
+				REVT_NOTIFY_DISABLE(r_evt,
+						    r_evt->evt->id, src_id);
+		}
+		retvals = 1;
+	}
+	mutex_unlock(&r_evt->sources_mtx);
+
+	return retvals ? 0 : -EINVAL;
+}
+
+static int scmi_enable_events(struct scmi_event_handler *hndl)
+{
+	int ret = 0;
+
+	if (!hndl->enabled) {
+		ret = __scmi_enable_evt(hndl->r_evt,
+					KEY_XTRACT_SRC_ID(hndl->key), true);
+		if (!ret)
+			hndl->enabled = true;
+	}
+
+	return ret;
+}
+
+static int scmi_disable_events(struct scmi_event_handler *hndl)
+{
+	int ret = 0;
+
+	if (hndl->enabled) {
+		ret = __scmi_enable_evt(hndl->r_evt,
+					KEY_XTRACT_SRC_ID(hndl->key), false);
+		if (!ret)
+			hndl->enabled = false;
+	}
+
+	return ret;
+}
+
+/**
+ * scmi_put_handler_unlocked()  - Put an event handler
+ * @ni: A reference to the notification instance to use
+ * @hndl: The event handler to act upon
+ *
+ * After having got exclusive access to the registered handlers hashtable,
+ * update the refcount and if @hndl is no more in use by anyone:
+ * * ask for events' generation disabling
+ * * unregister and free the handler itself
+ *
+ * Context: Assumes all the proper locking has been managed by the caller.
+ *
+ * Return: True if handler was freed (users dropped to zero)
+ */
+static bool scmi_put_handler_unlocked(struct scmi_notify_instance *ni,
+				      struct scmi_event_handler *hndl)
+{
+	bool freed = false;
+
+	if (refcount_dec_and_test(&hndl->users)) {
+		if (!IS_HNDL_PENDING(hndl))
+			scmi_disable_events(hndl);
+		scmi_free_event_handler(hndl);
+		freed = true;
+	}
+
+	return freed;
+}
+
+static void scmi_put_handler(struct scmi_notify_instance *ni,
+			     struct scmi_event_handler *hndl)
+{
+	bool freed;
+	u8 protocol_id;
+	struct scmi_registered_event *r_evt = hndl->r_evt;
+
+	mutex_lock(&ni->pending_mtx);
+	if (r_evt) {
+		protocol_id = r_evt->proto->id;
+		mutex_lock(&r_evt->proto->registered_mtx);
+	}
+
+	freed = scmi_put_handler_unlocked(ni, hndl);
+
+	if (r_evt) {
+		mutex_unlock(&r_evt->proto->registered_mtx);
+		/*
+		 * Only registered handler acquired protocol; must be here
+		 * released only AFTER unlocking registered_mtx, since
+		 * releasing a protocol can trigger its de-initialization
+		 * (ie. including r_evt and registered_mtx)
+		 */
+		if (freed)
+			scmi_protocol_release(ni->handle, protocol_id);
+	}
+	mutex_unlock(&ni->pending_mtx);
+}
+
+static void scmi_put_active_handler(struct scmi_notify_instance *ni,
+				    struct scmi_event_handler *hndl)
+{
+	bool freed;
+	struct scmi_registered_event *r_evt = hndl->r_evt;
+	u8 protocol_id = r_evt->proto->id;
+
+	mutex_lock(&r_evt->proto->registered_mtx);
+	freed = scmi_put_handler_unlocked(ni, hndl);
+	mutex_unlock(&r_evt->proto->registered_mtx);
+	if (freed)
+		scmi_protocol_release(ni->handle, protocol_id);
+}
+
+/**
+ * scmi_event_handler_enable_events()  - Enable events associated to an handler
+ * @hndl: The Event handler to act upon
+ *
+ * Return: 0 on Success
+ */
+static int scmi_event_handler_enable_events(struct scmi_event_handler *hndl)
+{
+	if (scmi_enable_events(hndl)) {
+		pr_err("Failed to ENABLE events for key:%X !\n", hndl->key);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/**
+ * scmi_notifier_register()  - Register a notifier_block for an event
+ * @handle: The handle identifying the platform instance against which the
+ *	    callback is registered
+ * @proto_id: Protocol ID
+ * @evt_id: Event ID
+ * @src_id: Source ID, when NULL register for events coming form ALL possible
+ *	    sources
+ * @nb: A standard notifier block to register for the specified event
+ *
+ * Generic helper to register a notifier_block against a protocol event.
+ *
+ * A notifier_block @nb will be registered for each distinct event identified
+ * by the tuple (proto_id, evt_id, src_id) on a dedicated notification chain
+ * so that:
+ *
+ *	(proto_X, evt_Y, src_Z) --> chain_X_Y_Z
+ *
+ * @src_id meaning is protocol specific and identifies the origin of the event
+ * (like domain_id, sensor_id and so forth).
+ *
+ * @src_id can be NULL to signify that the caller is interested in receiving
+ * notifications from ALL the available sources for that protocol OR simply that
+ * the protocol does not support distinct sources.
+ *
+ * As soon as one user for the specified tuple appears, an handler is created,
+ * and that specific event's generation is enabled at the platform level, unless
+ * an associated registered event is found missing, meaning that the needed
+ * protocol is still to be initialized and the handler has just been registered
+ * as still pending.
+ *
+ * Return: 0 on Success
+ */
+static int scmi_notifier_register(const struct scmi_handle *handle,
+				  u8 proto_id, u8 evt_id, const u32 *src_id,
+				  struct notifier_block *nb)
+{
+	int ret = 0;
+	u32 evt_key;
+	struct scmi_event_handler *hndl;
+	struct scmi_notify_instance *ni;
+
+	ni = scmi_notification_instance_data_get(handle);
+	if (!ni)
+		return -ENODEV;
+
+	evt_key = MAKE_HASH_KEY(proto_id, evt_id,
+				src_id ? *src_id : SRC_ID_MASK);
+	hndl = scmi_get_or_create_handler(ni, evt_key);
+	if (!hndl)
+		return -EINVAL;
+
+	blocking_notifier_chain_register(&hndl->chain, nb);
+
+	/* Enable events for not pending handlers */
+	if (!IS_HNDL_PENDING(hndl)) {
+		ret = scmi_event_handler_enable_events(hndl);
+		if (ret)
+			scmi_put_handler(ni, hndl);
+	}
+
+	return ret;
+}
+
+/**
+ * scmi_notifier_unregister()  - Unregister a notifier_block for an event
+ * @handle: The handle identifying the platform instance against which the
+ *	    callback is unregistered
+ * @proto_id: Protocol ID
+ * @evt_id: Event ID
+ * @src_id: Source ID
+ * @nb: The notifier_block to unregister
+ *
+ * Takes care to unregister the provided @nb from the notification chain
+ * associated to the specified event and, if there are no more users for the
+ * event handler, frees also the associated event handler structures.
+ * (this could possibly cause disabling of event's generation at platform level)
+ *
+ * Return: 0 on Success
+ */
+static int scmi_notifier_unregister(const struct scmi_handle *handle,
+				    u8 proto_id, u8 evt_id, const u32 *src_id,
+				    struct notifier_block *nb)
+{
+	u32 evt_key;
+	struct scmi_event_handler *hndl;
+	struct scmi_notify_instance *ni;
+
+	ni = scmi_notification_instance_data_get(handle);
+	if (!ni)
+		return -ENODEV;
+
+	evt_key = MAKE_HASH_KEY(proto_id, evt_id,
+				src_id ? *src_id : SRC_ID_MASK);
+	hndl = scmi_get_handler(ni, evt_key);
+	if (!hndl)
+		return -EINVAL;
+
+	/*
+	 * Note that this chain unregistration call is safe on its own
+	 * being internally protected by an rwsem.
+	 */
+	blocking_notifier_chain_unregister(&hndl->chain, nb);
+	scmi_put_handler(ni, hndl);
+
+	/*
+	 * This balances the initial get issued in @scmi_notifier_register.
+	 * If this notifier_block happened to be the last known user callback
+	 * for this event, the handler is here freed and the event's generation
+	 * stopped.
+	 *
+	 * Note that, an ongoing concurrent lookup on the delivery workqueue
+	 * path could still hold the refcount to 1 even after this routine
+	 * completes: in such a case it will be the final put on the delivery
+	 * path which will finally free this unused handler.
+	 */
+	scmi_put_handler(ni, hndl);
+
+	return 0;
+}
+
+struct scmi_notifier_devres {
+	const struct scmi_handle *handle;
+	u8 proto_id;
+	u8 evt_id;
+	u32 __src_id;
+	u32 *src_id;
+	struct notifier_block *nb;
+};
+
+static void scmi_devm_release_notifier(struct device *dev, void *res)
+{
+	struct scmi_notifier_devres *dres = res;
+
+	scmi_notifier_unregister(dres->handle, dres->proto_id, dres->evt_id,
+				 dres->src_id, dres->nb);
+}
+
+/**
+ * scmi_devm_notifier_register()  - Managed registration of a notifier_block
+ * for an event
+ * @sdev: A reference to an scmi_device whose embedded struct device is to
+ *	  be used for devres accounting.
+ * @proto_id: Protocol ID
+ * @evt_id: Event ID
+ * @src_id: Source ID, when NULL register for events coming form ALL possible
+ *	    sources
+ * @nb: A standard notifier block to register for the specified event
+ *
+ * Generic devres managed helper to register a notifier_block against a
+ * protocol event.
+ *
+ * Return: 0 on Success
+ */
+static int scmi_devm_notifier_register(struct scmi_device *sdev,
+				       u8 proto_id, u8 evt_id,
+				       const u32 *src_id,
+				       struct notifier_block *nb)
+{
+	int ret;
+	struct scmi_notifier_devres *dres;
+
+	dres = devres_alloc(scmi_devm_release_notifier,
+			    sizeof(*dres), GFP_KERNEL);
+	if (!dres)
+		return -ENOMEM;
+
+	ret = scmi_notifier_register(sdev->handle, proto_id,
+				     evt_id, src_id, nb);
+	if (ret) {
+		devres_free(dres);
+		return ret;
+	}
+
+	dres->handle = sdev->handle;
+	dres->proto_id = proto_id;
+	dres->evt_id = evt_id;
+	dres->nb = nb;
+	if (src_id) {
+		dres->__src_id = *src_id;
+		dres->src_id = &dres->__src_id;
+	} else {
+		dres->src_id = NULL;
+	}
+	devres_add(&sdev->dev, dres);
+
+	return ret;
+}
+
+static int scmi_devm_notifier_match(struct device *dev, void *res, void *data)
+{
+	struct scmi_notifier_devres *dres = res;
+	struct scmi_notifier_devres *xres = data;
+
+	if (WARN_ON(!dres || !xres))
+		return 0;
+
+	return dres->proto_id == xres->proto_id &&
+		dres->evt_id == xres->evt_id &&
+		dres->nb == xres->nb &&
+		((!dres->src_id && !xres->src_id) ||
+		  (dres->src_id && xres->src_id &&
+		   dres->__src_id == xres->__src_id));
+}
+
+/**
+ * scmi_devm_notifier_unregister()  - Managed un-registration of a
+ * notifier_block for an event
+ * @sdev: A reference to an scmi_device whose embedded struct device is to
+ *	  be used for devres accounting.
+ * @proto_id: Protocol ID
+ * @evt_id: Event ID
+ * @src_id: Source ID, when NULL register for events coming form ALL possible
+ *	    sources
+ * @nb: A standard notifier block to register for the specified event
+ *
+ * Generic devres managed helper to explicitly un-register a notifier_block
+ * against a protocol event, which was previously registered using the above
+ * @scmi_devm_notifier_register.
+ *
+ * Return: 0 on Success
+ */
+static int scmi_devm_notifier_unregister(struct scmi_device *sdev,
+					 u8 proto_id, u8 evt_id,
+					 const u32 *src_id,
+					 struct notifier_block *nb)
+{
+	int ret;
+	struct scmi_notifier_devres dres;
+
+	dres.handle = sdev->handle;
+	dres.proto_id = proto_id;
+	dres.evt_id = evt_id;
+	if (src_id) {
+		dres.__src_id = *src_id;
+		dres.src_id = &dres.__src_id;
+	} else {
+		dres.src_id = NULL;
+	}
+
+	ret = devres_release(&sdev->dev, scmi_devm_release_notifier,
+			     scmi_devm_notifier_match, &dres);
+
+	WARN_ON(ret);
+
+	return ret;
+}
+
+/**
+ * scmi_protocols_late_init()  - Worker for late initialization
+ * @work: The work item to use associated to the proper SCMI instance
+ *
+ * This kicks in whenever a new protocol has completed its own registration via
+ * scmi_register_protocol_events(): it is in charge of scanning the table of
+ * pending handlers (registered by users while the related protocol was still
+ * not initialized) and finalizing their initialization whenever possible;
+ * invalid pending handlers are purged at this point in time.
+ */
+static void scmi_protocols_late_init(struct work_struct *work)
+{
+	int bkt;
+	struct scmi_event_handler *hndl;
+	struct scmi_notify_instance *ni;
+	struct hlist_node *tmp;
+
+	ni = container_of(work, struct scmi_notify_instance, init_work);
+
+	/* Ensure protocols and events are up to date */
+	smp_rmb();
+
+	mutex_lock(&ni->pending_mtx);
+	hash_for_each_safe(ni->pending_events_handlers, bkt, tmp, hndl, hash) {
+		int ret;
+
+		ret = scmi_bind_event_handler(ni, hndl);
+		if (!ret) {
+			dev_dbg(ni->handle->dev,
+				"finalized PENDING handler - key:%X\n",
+				hndl->key);
+			ret = scmi_event_handler_enable_events(hndl);
+			if (ret) {
+				dev_dbg(ni->handle->dev,
+					"purging INVALID handler - key:%X\n",
+					hndl->key);
+				scmi_put_active_handler(ni, hndl);
+			}
+		} else {
+			ret = scmi_valid_pending_handler(ni, hndl);
+			if (ret) {
+				dev_dbg(ni->handle->dev,
+					"purging PENDING handler - key:%X\n",
+					hndl->key);
+				/* this hndl can be only a pending one */
+				scmi_put_handler_unlocked(ni, hndl);
+			}
+		}
+	}
+	mutex_unlock(&ni->pending_mtx);
+}
+
+/*
+ * notify_ops are attached to the handle so that can be accessed
+ * directly from an scmi_driver to register its own notifiers.
+ */
+static const struct scmi_notify_ops notify_ops = {
+	.devm_event_notifier_register = scmi_devm_notifier_register,
+	.devm_event_notifier_unregister = scmi_devm_notifier_unregister,
+	.event_notifier_register = scmi_notifier_register,
+	.event_notifier_unregister = scmi_notifier_unregister,
+};
+
+/**
+ * scmi_notification_init()  - Initializes Notification Core Support
+ * @handle: The handle identifying the platform instance to initialize
+ *
+ * This function lays out all the basic resources needed by the notification
+ * core instance identified by the provided handle: once done, all of the
+ * SCMI Protocols can register their events with the core during their own
+ * initializations.
+ *
+ * Note that failing to initialize the core notifications support does not
+ * cause the whole SCMI Protocols stack to fail its initialization.
+ *
+ * SCMI Notification Initialization happens in 2 steps:
+ * * initialization: basic common allocations (this function)
+ * * registration: protocols asynchronously come into life and registers their
+ *		   own supported list of events with the core; this causes
+ *		   further per-protocol allocations
+ *
+ * Any user's callback registration attempt, referring a still not registered
+ * event, will be registered as pending and finalized later (if possible)
+ * by scmi_protocols_late_init() work.
+ * This allows for lazy initialization of SCMI Protocols due to late (or
+ * missing) SCMI drivers' modules loading.
+ *
+ * Return: 0 on Success
+ */
+int scmi_notification_init(struct scmi_handle *handle)
+{
+	void *gid;
+	struct scmi_notify_instance *ni;
+
+	gid = devres_open_group(handle->dev, NULL, GFP_KERNEL);
+	if (!gid)
+		return -ENOMEM;
+
+	ni = devm_kzalloc(handle->dev, sizeof(*ni), GFP_KERNEL);
+	if (!ni)
+		goto err;
+
+	ni->gid = gid;
+	ni->handle = handle;
+
+	ni->registered_protocols = devm_kcalloc(handle->dev, SCMI_MAX_PROTO,
+						sizeof(char *), GFP_KERNEL);
+	if (!ni->registered_protocols)
+		goto err;
+
+	ni->notify_wq = alloc_workqueue(dev_name(handle->dev),
+					WQ_UNBOUND | WQ_FREEZABLE | WQ_SYSFS,
+					0);
+	if (!ni->notify_wq)
+		goto err;
+
+	mutex_init(&ni->pending_mtx);
+	hash_init(ni->pending_events_handlers);
+
+	INIT_WORK(&ni->init_work, scmi_protocols_late_init);
+
+	scmi_notification_instance_data_set(handle, ni);
+	handle->notify_ops = &notify_ops;
+	/* Ensure handle is up to date */
+	smp_wmb();
+
+	dev_info(handle->dev, "Core Enabled.\n");
+
+	devres_close_group(handle->dev, ni->gid);
+
+	return 0;
+
+err:
+	dev_warn(handle->dev, "Initialization Failed.\n");
+	devres_release_group(handle->dev, gid);
+	return -ENOMEM;
+}
+
+/**
+ * scmi_notification_exit()  - Shutdown and clean Notification core
+ * @handle: The handle identifying the platform instance to shutdown
+ */
+void scmi_notification_exit(struct scmi_handle *handle)
+{
+	struct scmi_notify_instance *ni;
+
+	ni = scmi_notification_instance_data_get(handle);
+	if (!ni)
+		return;
+	scmi_notification_instance_data_set(handle, NULL);
+
+	/* Destroy while letting pending work complete */
+	destroy_workqueue(ni->notify_wq);
+
+	devres_release_group(ni->handle->dev, ni->gid);
+}