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Subject[PATCH v4 06/13] firmware: arm_scmi: Add notification callbacks-registration
Date
Add core SCMI Notifications callbacks-registration support: allow users
to register their own callbacks against the desired events.
Whenever a registration request is issued against a still non existent
event, mark such request as pending for later processing, in order to
account for possible late initializations of SCMI Protocols associated
to loadable drivers.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
V3 --> V4
- split registered_handlers hashtable on a per-protocol basis to reduce
unneeded contention
- introduced pending_handlers table and related late_init worker to finalize
handlers registration upon effective protocols' registrations
- introduced further safe accessors macros for registered_protocols
and registered_events arrays
V2 --> V3
- refactored get/put event_handler
- removed generic non-handle-based API
V1 --> V2
- splitted out of V1 patch 04
- moved from IDR maps to real HashTables to store event_handlers
- added proper enable_events refcounting via __scmi_enable_evt()
[was broken in V1 when using ALL_SRCIDs notification chains]
- reviewed hashtable cleanup strategy in scmi_notifications_exit()
- added scmi_register_event_notifier()/scmi_unregister_event_notifier()
to include/linux/scmi_protocol.h as a candidate user API
[no EXPORTs still]
- added notify_ops to handle during initialization as an additional
internal API for scmi_drivers
---
drivers/firmware/arm_scmi/notify.c | 700 +++++++++++++++++++++++++++++
drivers/firmware/arm_scmi/notify.h | 12 +
include/linux/scmi_protocol.h | 50 +++
3 files changed, 762 insertions(+)

diff --git a/drivers/firmware/arm_scmi/notify.c b/drivers/firmware/arm_scmi/notify.c
index 31e49cb7d88e..d6c08cce3c63 100644
--- a/drivers/firmware/arm_scmi/notify.c
+++ b/drivers/firmware/arm_scmi/notify.c
@@ -16,18 +16,50 @@
* this core its set of supported events using @scmi_register_protocol_events():
* all the needed descriptors are stored in the @registered_protocols and
* @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).
*/

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/atomic.h>
+#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/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>
@@ -47,6 +79,71 @@
#define MAKE_ALL_SRCS_KEY(p, e) \
MAKE_HASH_KEY((p), (e), SCMI_ALL_SRC_IDS)

+/**
+ * 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) \
+({ \
+ hash_for_each_possible((__ht), (__obj), hash, (__k)) \
+ if (likely((__obj)->key == (__k))) \
+ break; \
+ __obj; \
+})
+
+#define PROTO_ID_MASK GENMASK(31, 24)
+#define EVT_ID_MASK GENMASK(23, 16)
+#define SRC_ID_MASK GENMASK(15, 0)
+#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) \
+({ \
+ struct scmi_registered_protocol_events_desc *__pd = NULL; \
+ \
+ if ((__ni) && (__pid) < SCMI_MAX_PROTO) \
+ __pd = READ_ONCE((__ni)->registered_protocols[(__pid)]);\
+ __pd; \
+})
+
+#define SCMI_GET_REVT_FROM_PD(__pd, __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 = NULL; \
+ struct scmi_registered_protocol_events_desc *__pd = NULL; \
+ \
+ __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_ENABLE(revt, ...) \
+ ((revt)->proto->ops->set_notify_enabled((revt)->proto->ni->handle, \
+ __VA_ARGS__))
+
struct scmi_registered_protocol_events_desc;

/**
@@ -60,16 +157,25 @@ struct scmi_registered_protocol_events_desc;
* @initialized: A flag that indicates if the core resources have been allocated
* and protocols are allowed to register their supported events
* @enabled: A flag to indicate events can be enabled and start flowing
+ * @init_work: A work item to perform final initializations of pending handlers
+ * @pending_mtx: A mutex to protect @pending_events_handlers
* @registered_protocols: An 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
*/
struct scmi_notify_instance {
void *gid;
struct scmi_handle *handle;
atomic_t initialized;
atomic_t enabled;
+
+ struct work_struct init_work;
+
+ struct mutex pending_mtx;
struct scmi_registered_protocol_events_desc **registered_protocols;
+ DECLARE_HASHTABLE(pending_events_handlers, 8);
};

/**
@@ -132,6 +238,9 @@ struct scmi_registered_event;
* @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
+ * @registered_events_handlers: An hashtable containing all events' handlers
+ * descriptors registered for this protocol
*/
struct scmi_registered_protocol_events_desc {
u8 id;
@@ -143,6 +252,8 @@ struct scmi_registered_protocol_events_desc {
void *in_flight;
int num_events;
struct scmi_registered_event **registered_events;
+ struct mutex registered_mtx;
+ DECLARE_HASHTABLE(registered_events_handlers, 8);
};

/**
@@ -175,6 +286,38 @@ struct scmi_registered_event {
struct mutex sources_mtx;
};

+/**
+ * scmi_event_handler - Event handler information
+ *
+ * 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.
+ *
+ * @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
+ */
+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 == NULL)
+
+static void scmi_put_handler_unlocked(struct scmi_notify_instance *ni,
+ struct scmi_event_handler *hndl);
/**
* scmi_initialize_events_queue - Allocate/Initialize a kfifo buffer
*
@@ -252,6 +395,10 @@ scmi_allocate_registered_protocol_desc(struct scmi_notify_instance *ni,
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;
}

@@ -338,6 +485,12 @@ int scmi_register_protocol_events(const struct scmi_handle *handle,

devres_close_group(ni->handle->dev, ni->gid);

+ /*
+ * Finalize any pending events' handler which could have been waiting
+ * for this protocol's events registration.
+ */
+ schedule_work(&ni->init_work);
+
return 0;

err:
@@ -349,6 +502,547 @@ int scmi_register_protocol_events(const struct scmi_handle *handle,
return -ENOMEM;
}

+/**
+ * scmi_allocate_event_handler - Allocate Event handler
+ *
+ * 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.
+ *
+ * Assumes to be called with @pending_mtx already acquired.
+ *
+ * @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)
+ *
+ * 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 ERR_PTR(-ENOMEM);
+ 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
+ *
+ * Assumes to be called with proper locking acquired depending on the situation.
+ *
+ * @hndl: The event handler structure to free
+ */
+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
+ *
+ * If an associated registered event is found, move the handler from the pending
+ * into the registered table.
+ *
+ * Assumes to be called with @pending_mtx already acquired.
+ *
+ * @ni: A reference to the notification instance to use
+ * @hndl: The event handler to bind
+ *
+ * Return: True if bind was successful, False otherwise
+ */
+static inline bool 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 (unlikely(!r_evt))
+ return false;
+
+ /* Remove from pending and insert into registered */
+ hash_del(&hndl->hash);
+ 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 true;
+}
+
+/**
+ * scmi_valid_pending_handler - Helper to check pending status of handlers
+ *
+ * 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.
+ *
+ * @ni: A reference to the notification instance to use
+ * @hndl: The event handler to check
+ *
+ * Return: True if pending registration is still valid, False otherwise.
+ */
+static inline bool scmi_valid_pending_handler(struct scmi_notify_instance *ni,
+ struct scmi_event_handler *hndl)
+{
+ struct scmi_registered_protocol_events_desc *pd;
+
+ if (unlikely(!IS_HNDL_PENDING(hndl)))
+ return false;
+
+ pd = SCMI_GET_PROTO(ni, KEY_XTRACT_PROTO_ID(hndl->key));
+ if (pd)
+ return false;
+
+ return true;
+}
+
+/**
+ * scmi_register_event_handler - Register whenever possible an Event handler
+ *
+ * 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.
+ *
+ * Assumes to be called with @pending_mtx acquired.
+ *
+ * @ni: A reference to the notification instance to use
+ * @hndl: The event handler to register
+ *
+ * Return: True if a normal or a valid pending registration has been completed,
+ * False otherwise
+ */
+static bool scmi_register_event_handler(struct scmi_notify_instance *ni,
+ struct scmi_event_handler *hndl)
+{
+ bool ret;
+
+ ret = scmi_bind_event_handler(ni, hndl);
+ if (ret) {
+ pr_info("SCMI Notifications: registered NEW handler - key:%X\n",
+ hndl->key);
+ } else {
+ ret = scmi_valid_pending_handler(ni, hndl);
+ if (ret)
+ pr_info("SCMI Notifications: registered PENDING handler - key:%X\n",
+ hndl->key);
+ }
+
+ return ret;
+}
+
+/**
+ * __scmi_event_handler_get_ops - Utility to get or create an event handler
+ *
+ * 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.
+ *
+ * @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
+ *
+ * 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 (likely(r_evt)) {
+ mutex_lock(&r_evt->proto->registered_mtx);
+ hndl = KEY_FIND(r_evt->proto->registered_events_handlers,
+ hndl, evt_key);
+ if (likely(hndl))
+ refcount_inc(&hndl->users);
+ mutex_unlock(&r_evt->proto->registered_mtx);
+ }
+
+ /* ...then amongst pending. */
+ if (unlikely(!hndl)) {
+ hndl = KEY_FIND(ni->pending_events_handlers, hndl, evt_key);
+ if (likely(hndl))
+ refcount_inc(&hndl->users);
+ }
+
+ /* Create if still not found and required */
+ if (!hndl && create) {
+ hndl = scmi_allocate_event_handler(ni, evt_key);
+ if (!IS_ERR_OR_NULL(hndl)) {
+ if (!scmi_register_event_handler(ni, hndl)) {
+ pr_info("SCMI Notifications: 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_enable_evt - Enable/disable events generation
+ *
+ * Takes care of proper refcounting while performing enable/disable: handles
+ * the special case of ALL sources requests by itself.
+ *
+ * @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
+ *
+ * Return: True when the required @action has been successfully executed
+ */
+static inline bool __scmi_enable_evt(struct scmi_registered_event *r_evt,
+ u32 src_id, bool enable)
+{
+ int ret = 0;
+ u32 num_sources;
+ refcount_t *sid;
+
+ if (src_id == SCMI_ALL_SRC_IDS) {
+ src_id = 0;
+ num_sources = r_evt->num_sources;
+ } else if (src_id < r_evt->num_sources) {
+ num_sources = 1;
+ } else {
+ return ret;
+ }
+
+ mutex_lock(&r_evt->sources_mtx);
+ if (enable) {
+ for (; num_sources; src_id++, num_sources--) {
+ bool r;
+
+ sid = &r_evt->sources[src_id];
+ if (refcount_read(sid) == 0) {
+ r = REVT_NOTIFY_ENABLE(r_evt,
+ r_evt->evt->id,
+ src_id, enable);
+ if (r)
+ refcount_set(sid, 1);
+ } else {
+ refcount_inc(sid);
+ r = true;
+ }
+ ret += r;
+ }
+ } else {
+ for (; num_sources; src_id++, num_sources--) {
+ sid = &r_evt->sources[src_id];
+ if (refcount_dec_and_test(sid))
+ REVT_NOTIFY_ENABLE(r_evt,
+ r_evt->evt->id,
+ src_id, enable);
+ }
+ ret = 1;
+ }
+ mutex_unlock(&r_evt->sources_mtx);
+
+ return ret;
+}
+
+static bool scmi_enable_events(struct scmi_event_handler *hndl)
+{
+ if (!hndl->enabled)
+ hndl->enabled = __scmi_enable_evt(hndl->r_evt,
+ KEY_XTRACT_SRC_ID(hndl->key),
+ true);
+ return hndl->enabled;
+}
+
+static bool scmi_disable_events(struct scmi_event_handler *hndl)
+{
+ if (hndl->enabled)
+ hndl->enabled = !__scmi_enable_evt(hndl->r_evt,
+ KEY_XTRACT_SRC_ID(hndl->key),
+ false);
+ return !hndl->enabled;
+}
+
+/**
+ * scmi_put_handler_unlocked - Put an event handler
+ *
+ * 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
+ *
+ * Assumes all the proper locking has been managed by the caller.
+ *
+ * @ni: A reference to the notification instance to use
+ * @hndl: The event handler to act upon
+ */
+
+static void
+scmi_put_handler_unlocked(struct scmi_notify_instance *ni,
+ struct scmi_event_handler *hndl)
+{
+ if (refcount_dec_and_test(&hndl->users)) {
+ if (likely(!IS_HNDL_PENDING(hndl)))
+ scmi_disable_events(hndl);
+ scmi_free_event_handler(hndl);
+ }
+}
+
+static void scmi_put_handler(struct scmi_notify_instance *ni,
+ struct scmi_event_handler *hndl)
+{
+ struct scmi_registered_event *r_evt = hndl->r_evt;
+
+ mutex_lock(&ni->pending_mtx);
+ if (r_evt)
+ mutex_lock(&r_evt->proto->registered_mtx);
+
+ scmi_put_handler_unlocked(ni, hndl);
+
+ if (r_evt)
+ mutex_unlock(&r_evt->proto->registered_mtx);
+ mutex_unlock(&ni->pending_mtx);
+}
+
+/**
+ * scmi_event_handler_enable_events - Enable events associated to an handler
+ *
+ * @hndl: The Event handler to act upon
+ *
+ * Return: True on success
+ */
+static bool scmi_event_handler_enable_events(struct scmi_event_handler *hndl)
+{
+ if (!scmi_enable_events(hndl)) {
+ pr_err("SCMI Notifications: Failed to ENABLE events for key:%X !\n",
+ hndl->key);
+ return false;
+ }
+
+ return true;
+}
+
+/**
+ * scmi_register_notifier - Register a notifier_block for an 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.
+ *
+ * @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
+ *
+ * Return: Return 0 on Success
+ */
+static int scmi_register_notifier(const struct scmi_handle *handle,
+ u8 proto_id, u8 evt_id, u32 *src_id,
+ struct notifier_block *nb)
+{
+ int ret = 0;
+ u32 evt_key;
+ struct scmi_event_handler *hndl;
+ struct scmi_notify_instance *ni = handle->notify_priv;
+
+ if (unlikely(!ni || !atomic_read(&ni->initialized)))
+ return 0;
+
+ evt_key = MAKE_HASH_KEY(proto_id, evt_id,
+ src_id ? *src_id : SCMI_ALL_SRC_IDS);
+ hndl = scmi_get_or_create_handler(ni, evt_key);
+ if (IS_ERR_OR_NULL(hndl))
+ return PTR_ERR(hndl);
+
+ blocking_notifier_chain_register(&hndl->chain, nb);
+
+ /* Enable events for not pending handlers */
+ if (likely(!IS_HNDL_PENDING(hndl))) {
+ if (!scmi_event_handler_enable_events(hndl)) {
+ scmi_put_handler(ni, hndl);
+ ret = -EINVAL;
+ }
+ }
+
+ return ret;
+}
+
+/**
+ * scmi_unregister_notifier - Unregister a notifier_block for an event
+ *
+ * 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)
+ *
+ * @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
+ *
+ * Return: 0 on Success
+ */
+static int scmi_unregister_notifier(const struct scmi_handle *handle,
+ u8 proto_id, u8 evt_id, u32 *src_id,
+ struct notifier_block *nb)
+{
+ u32 evt_key;
+ struct scmi_event_handler *hndl;
+ struct scmi_notify_instance *ni = handle->notify_priv;
+
+ if (unlikely(!ni || !atomic_read(&ni->initialized)))
+ return 0;
+
+ evt_key = MAKE_HASH_KEY(proto_id, evt_id,
+ src_id ? *src_id : SCMI_ALL_SRC_IDS);
+ hndl = scmi_get_handler(ni, evt_key);
+ if (IS_ERR_OR_NULL(hndl))
+ return -EINVAL;
+
+ blocking_notifier_chain_unregister(&hndl->chain, nb);
+ scmi_put_handler(ni, hndl);
+
+ /*
+ * Free the handler (and stop events) if this happens to be the last
+ * known user callback for this handler; a possible concurrently ongoing
+ * run of @scmi_lookup_and_call_event_chain will cause this to happen
+ * in that context safely instead.
+ */
+ scmi_put_handler(ni, hndl);
+
+ return 0;
+}
+
+/**
+ * scmi_protocols_late_init - Worker for late initialization
+ *
+ * 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.
+ *
+ * @work: The work item to use associated to the proper SCMI instance
+ */
+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);
+
+ mutex_lock(&ni->pending_mtx);
+ hash_for_each_safe(ni->pending_events_handlers, bkt, tmp, hndl, hash) {
+ bool ret;
+
+ ret = scmi_bind_event_handler(ni, hndl);
+ if (ret) {
+ pr_info("SCMI Notifications: finalized PENDING handler - key:%X\n",
+ hndl->key);
+ ret = scmi_event_handler_enable_events(hndl);
+ } else {
+ ret = scmi_valid_pending_handler(ni, hndl);
+ }
+ if (!ret) {
+ pr_info("SCMI Notifications: 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 struct scmi_notify_ops notify_ops = {
+ .register_event_notifier = scmi_register_notifier,
+ .unregister_event_notifier = scmi_unregister_notifier,
+};
+
/**
* scmi_notification_init - Initializes Notification Core Support
*
@@ -398,7 +1092,13 @@ int scmi_notification_init(struct scmi_handle *handle)
if (!ni->registered_protocols)
goto err;

+ mutex_init(&ni->pending_mtx);
+ hash_init(ni->pending_events_handlers);
+
+ INIT_WORK(&ni->init_work, scmi_protocols_late_init);
+
handle->notify_priv = ni;
+ handle->notify_ops = &notify_ops;

atomic_set(&ni->initialized, 1);
atomic_set(&ni->enabled, 1);
diff --git a/drivers/firmware/arm_scmi/notify.h b/drivers/firmware/arm_scmi/notify.h
index a7ece64e8842..f765acda2311 100644
--- a/drivers/firmware/arm_scmi/notify.h
+++ b/drivers/firmware/arm_scmi/notify.h
@@ -9,9 +9,21 @@
#ifndef _SCMI_NOTIFY_H
#define _SCMI_NOTIFY_H

+#include <linux/bug.h>
#include <linux/device.h>
#include <linux/types.h>

+#define MAP_EVT_TO_ENABLE_CMD(id, map) \
+({ \
+ int ret = -1; \
+ \
+ if (likely((id) < ARRAY_SIZE((map)))) \
+ ret = (map)[(id)]; \
+ else \
+ WARN(1, "UN-KNOWN evt_id:%d\n", (id)); \
+ ret; \
+})
+
/**
* scmi_event - Describes an event to be supported
*
diff --git a/include/linux/scmi_protocol.h b/include/linux/scmi_protocol.h
index 0679f10ab05e..797e1e03ae52 100644
--- a/include/linux/scmi_protocol.h
+++ b/include/linux/scmi_protocol.h
@@ -9,6 +9,8 @@
#define _LINUX_SCMI_PROTOCOL_H

#include <linux/device.h>
+#include <linux/ktime.h>
+#include <linux/notifier.h>
#include <linux/types.h>

#define SCMI_MAX_STR_SIZE 16
@@ -211,6 +213,52 @@ struct scmi_reset_ops {
int (*deassert)(const struct scmi_handle *handle, u32 domain);
};

+/**
+ * scmi_notify_ops - represents notifications' operations provided by SCMI core
+ *
+ * A user can register/unregister its own notifier_block against the wanted
+ * platform instance regarding the desired event identified by the
+ * tuple: (proto_id, evt_id, src_id)
+ *
+ * @register_event_notifier: Register a notifier_block for the requested event
+ * @unregister_event_notifier: Unregister a notifier_block for the requested
+ * event
+ *
+ * where:
+ *
+ * @handle: The handle identifying the platform instance to use
+ * @proto_id: The protocol ID as in SCMI Specification
+ * @evt_id: The message ID of the desired event as in SCMI Specification
+ * @src_id: A pointer to the desired source ID if different sources are
+ * possible for the protocol (like domain_id, sensor_id...etc)
+ *
+ * @src_id can be provided as NULL if it simply does NOT make sense for
+ * the protocol at hand, OR if the user is explicitly interested in
+ * receiving notifications from ANY existent source associated to the
+ * specified proto_id / evt_id.
+ *
+ * Received notifications are finally delivered to the registered users,
+ * invoking the callback provided with the notifier_block *nb as follows:
+ *
+ * int user_cb(nb, evt_id, report)
+ *
+ * with:
+ *
+ * @nb: The notifier block provided by the user
+ * @evt_id: The message ID of the delivered event
+ * @report: A custom struct describing the specific event delivered
+ *
+ * Events' customized report structs are detailed in the following.
+ */
+struct scmi_notify_ops {
+ int (*register_event_notifier)(const struct scmi_handle *handle,
+ u8 proto_id, u8 evt_id, u32 *src_id,
+ struct notifier_block *nb);
+ int (*unregister_event_notifier)(const struct scmi_handle *handle,
+ u8 proto_id, u8 evt_id, u32 *src_id,
+ struct notifier_block *nb);
+};
+
/**
* struct scmi_handle - Handle returned to ARM SCMI clients for usage.
*
@@ -221,6 +269,7 @@ struct scmi_reset_ops {
* @clk_ops: pointer to set of clock protocol operations
* @sensor_ops: pointer to set of sensor protocol operations
* @reset_ops: pointer to set of reset protocol operations
+ * @notify_ops: pointer to set of notifications related operations
* @perf_priv: pointer to private data structure specific to performance
* protocol(for internal use only)
* @clk_priv: pointer to private data structure specific to clock
@@ -242,6 +291,7 @@ struct scmi_handle {
struct scmi_power_ops *power_ops;
struct scmi_sensor_ops *sensor_ops;
struct scmi_reset_ops *reset_ops;
+ struct scmi_notify_ops *notify_ops;
/* for protocol internal use */
void *perf_priv;
void *clk_priv;
--
2.17.1
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