[RFC PATCH 04/11] firmware: arm_scmi: Add core notifications support

[Cristian Marussi <cristian.marussi@arm.com>]

Add basic support for SCMI Notifications, using Kernel notification chains
mechanism.

Each SCMI Protocol has a dedicated events' queue and deferred worker which
is in charge of delivering the notifications to the interested users
invoking the users' registered callbacks.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
 drivers/firmware/arm_scmi/Makefile |   2 +-
 drivers/firmware/arm_scmi/common.h |   4 +
 drivers/firmware/arm_scmi/driver.c |   2 +
 drivers/firmware/arm_scmi/notify.c | 904 +++++++++++++++++++++++++++++
 drivers/firmware/arm_scmi/notify.h |  79 +++
 5 files changed, 990 insertions(+), 1 deletion(-)
 create mode 100644 drivers/firmware/arm_scmi/notify.c
 create mode 100644 drivers/firmware/arm_scmi/notify.h

diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
index 5f298f00a82e..26587ea4661f 100644
--- a/drivers/firmware/arm_scmi/Makefile
+++ b/drivers/firmware/arm_scmi/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-y	= scmi-bus.o scmi-driver.o scmi-protocols.o
 scmi-bus-y = bus.o
-scmi-driver-y = driver.o
+scmi-driver-y = driver.o notify.o
 scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o
 obj-$(CONFIG_ARM_SCMI_POWER_DOMAIN) += scmi_pm_domain.o
diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
index df35358ff324..2621c05e9149 100644
--- a/drivers/firmware/arm_scmi/common.h
+++ b/drivers/firmware/arm_scmi/common.h
@@ -6,6 +6,8 @@
  *
  * Copyright (C) 2018 ARM Ltd.
  */
+#ifndef _SCMI_COMMON_H
+#define _SCMI_COMMON_H
 
 #include <linux/bitfield.h>
 #include <linux/completion.h>
@@ -113,3 +115,5 @@ void scmi_setup_protocol_implemented(const struct scmi_handle *handle,
 				     u8 *prot_imp);
 
 int scmi_base_protocol_init(struct scmi_handle *h);
+
+#endif /* _SCMI_COMMON_H */
diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index 28ed1f0cb417..a43fad29de11 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -350,12 +350,14 @@ __scmi_xfer_put(struct scmi_xfers_info *minfo, struct scmi_xfer *xfer)
 
 static void scmi_handle_notification(struct scmi_chan_info *cinfo, u32 msg_hdr)
 {
+	ktime_t ts;
 	struct scmi_xfer *xfer;
 	struct device *dev = cinfo->dev;
 	struct scmi_info *info = handle_to_scmi_info(cinfo->handle);
 	struct scmi_xfers_info *minfo = &info->rx_minfo;
 	struct scmi_shared_mem __iomem *mem = cinfo->payload;
 
+	ts = ktime_get_boottime();
 	xfer = scmi_xfer_get(cinfo->handle, minfo);
 	if (IS_ERR(xfer)) {
 		dev_err(dev, "failed to get free message slot (%ld)\n",
diff --git a/drivers/firmware/arm_scmi/notify.c b/drivers/firmware/arm_scmi/notify.c
new file mode 100644
index 000000000000..da342f43021e
--- /dev/null
+++ b/drivers/firmware/arm_scmi/notify.c
@@ -0,0 +1,904 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * System Control and Management Interface (SCMI) Notification support
+ *
+ * Copyright (C) 2019 ARM Ltd.
+ *
+ * SCMI Protocol specification allows the platform to signal events to
+ * interested agents via notification messages: this in an implementation
+ * of the dispatch and delivery of such notifications to the interested users
+ * inside the Linux kernel.
+ *
+ * Each SCMI Protocol implementation, during its initialization, registers with
+ * this core notification framework its set of supported events via
+ * @scmi_register_protocol_events(), while Kernel users interested in some
+ * specific event can register their associated callbacks providing the usual
+ * notifier_block descriptor, since the notification system internally supports
+ * events delivery using customized notification chains.
+ *
+ * Given the number of possible events defined by SCMI and the extensibility
+ * of the SCMI Protocol itself, such underlying notification chains are created
+ * and destroyed dynamically on demand depending on the number of users
+ * effectively registered for an event, so that no 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.
+ *
+ * An event is identified univocally by the tuple (proto_id, evt_id, src_id)
+ * and is served by its own dedicated notification chain: given that such chain
+ * is dynamically created, the registration API simply let the users associate
+ * their callbacks with the above tuple.
+ *
+ * Here proto_id and evt_id are simply the protocol_id and message_id numbers as
+ * reported 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), so that a user can register its callbacks for a
+ * particular event coming only from a defined source (like CPU vs GPU).
+ * When the source is not specified the user callback will be registered for
+ * all existing sources for that event (if any).
+ *
+ * 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,
+ * in turn, after having looked up the event in the registered events mapping,
+ * pushes the event-data itself on a protocol dedicated kfifo queue for deferred
+ * processing.
+ *
+ * Such dedicated protocols' queues are allocated once for all at initialization
+ * time, together with a dedicated work_item running the common delivery logic
+ * of @scmi_events_dispatcher(), so that each protocol has it own dedicated
+ * worker which, once kicked by the ISR, takes care to empty is own dedicated
+ * queue deliverying the queued items into the proper notification chain.
+ * Note that since the underlying cmwq workers run one distinct work_item per
+ * protocol and there are a number of max-active workers equal to the number of
+ * protocols, notifications processing can proceed concurrently only between
+ * events belonging to different protocols, while delivery of events within the
+ * same protocol is still strictly sequentially ordered by time of arrival; this
+ * separation effectively avoids the possibility that one particularly verbose
+ * protocol, flooding the queues with events, can cause other protocols' events
+ * to be lost or their processing starved.
+ *
+ * Event's information is converted to a custom per-event report struct before
+ * being fed as void *data param to the user callback embedded in the registered
+ * notifier_block so that it looks like as follow from the user perspective:
+ *
+ * int user_cb(struct notifier_block *nb, unsigned long event_id, void *report)
+ *
+ *
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/bug.h>
+#include <linux/bitfield.h>
+#include <linux/err.h>
+#include <linux/idr.h>
+#include <linux/kernel.h>
+#include <linux/kfifo.h>
+#include <linux/notifier.h>
+#include <linux/refcount.h>
+#include <linux/slab.h>
+#include <linux/scmi_protocol.h>
+#include <linux/types.h>
+#include <linux/workqueue.h>
+
+#include "notify.h"
+
+#define SCMI_NOTIF_MAX_ACTIVE_QUEUES	7
+
+/*
+ * Builds an unsigned 32bit key from the given input tuple to be used as a key
+ * in IDR mappings; note that if __src_p is passed in as NULL, the returned key
+ * is built using SCMI_ALL_SRC_IDS as src_id.
+ */
+#define MAKE_EVT_KEY(__proto, __evt, __src_p)				\
+	({								\
+		u32 __evt_key, __src_id;				\
+									\
+		__src_id = ((__src_p)) ?				\
+			    (*((u32 *)(__src_p)) & SCMI_ALL_SRC_IDS) :	\
+			    SCMI_ALL_SRC_IDS;				\
+		__evt_key = ((__proto) << 24) |				\
+				((__evt) << 16) | __src_id;		\
+		__evt_key;						\
+	})
+
+#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))
+
+/**
+ * events_queue  - Describes a queue and its associated worker
+ *
+ * Each protocol has its own dedicated events_queue descriptor.
+ *
+ * @sz: Size in bytes of the related kfifo
+ * @kfifo: A dedicated Kernel kfifo
+ * @notify_work: A custom work item bound to this queue
+ * @wq: A reference to the related workqueue
+ */
+struct events_queue {
+	size_t			sz;
+	struct kfifo		kfifo;
+	struct work_struct	notify_work;
+	struct workqueue_struct	*wq;
+};
+
+/**
+ * scmi_registered_protocol_events_desc  - Protocol Specific information
+ *
+ * All protocols that registers at least an event have their protocol-specific
+ * information stored here, together with a pointer to the allocated
+ * events_queue.
+ *
+ * @id: Protocol ID
+ * @ops: Protocol specific and event-related operations
+ * @equeue: A reference to the associated per-protocol events_queue
+ */
+struct scmi_registered_protocol_events_desc {
+	u8					id;
+	const struct scmi_protocol_event_ops	*ops;
+	struct events_queue			*equeue;
+};
+
+/**
+ * scmi_registered_event  - Event Specific Information
+ *
+ * All registered events are represented by one of these structures.
+ *
+ * @proto: A reference to the associated protocol descriptor
+ * @evt: A reference to the associated event descriptor (as provided at
+ *       registration time)
+ * @scratch_isr: A pre-allocated buffer to be used as a scratch area by ISR
+ * @scratch_isr: A pre-allocated buffer to be used as a scratch area by the
+ *		 deferred worker
+ * @report: A pre-allocated buffer used by the deferred workr to fill a
+ *	    customized event report
+ */
+struct scmi_registered_event {
+	struct scmi_registered_protocol_events_desc	*proto;
+	const struct scmi_event				*evt;
+	void						*scratch_isr;
+	void						*scratch_bh;
+	void						*report;
+};
+
+/**
+ * scmi_event_handler  - Event handler information
+ *
+ * This structure collects all the information needed to process a received
+ * event, calling all the registered notifier callbacks.
+ * Note this an event handler is associated to a tuple of values like:
+ *	(proto_id, evt_id, src_id)
+ * through the means of a key and an IDR mapping.
+ *
+ * @evt_key: The unsigned 32bit key associated to this descriptor in the
+ *	     related IDR mapping
+ * @r_evt: A reference to the underlying registered event
+ * @chain: The notification chain dedicated to this specific event tuple
+ */
+struct scmi_event_handler {
+	u32				evt_key;
+	bool				enabled;
+	refcount_t			users;
+	struct scmi_registered_event	*r_evt;
+	struct blocking_notifier_head	chain;
+};
+
+/**
+ * scmi_event_header  - A utility header
+ *
+ * This header is prepended to each received event message payload before
+ * being queued on the related events_queue, and describes the attached event
+ * message.
+ *
+ * @timestamp: The timestamp, innanoseconds (boottime), which was associated
+ *	       to this event as soon as it entered the SCMI RX ISR
+ * @proto_id: Protocol ID
+ * @evt_id: Event ID (corresponds to the Event MsgID for this Protocol)
+ * @payld_sz: Effective size of the attached message payload which follows
+ * @payld: A reference to the included Event payload
+ */
+struct scmi_event_header {
+	u64	timestamp;
+	u8	proto_id;
+	u8	evt_id;
+	size_t	payld_sz;
+	u8	payld[];
+} __packed;
+
+/*
+ * A few IDR maps to track:
+ *
+ * - @scmi_registered_events: All event's descriptors registered by the
+ *			      protocols, together with their ancillary data
+ * - @scmi_registered_events_handlers: All event's handlers descriptors, created
+ *				       to collect all the users' notifier_block
+ *				       callbacks and related notification chains
+ * - @scmi_registered_protocols: All protocol-level specific information related
+ *				 to events' handling
+ */
+static struct idr scmi_registered_events;
+static struct idr scmi_registered_events_handlers;
+static DEFINE_MUTEX(scmi_registered_events_handler_mtx);
+static struct idr scmi_registered_protocols;
+
+/* Common Kernel cmwq workqueue used by notifications core */
+static struct workqueue_struct *scmi_notify_wq;
+
+static bool scmi_notifications_initialized;
+
+static struct scmi_event_handler *scmi_get_event_handler(u32 evt_key);
+static void scmi_put_event_handler(struct scmi_event_handler *hndl);
+
+/**
+ * scmi_discard_bad_evt_payloadi() - Discard data from a kfifo
+ *
+ * @kq: The kfifo to act on
+ * @count: Number of bytes to flush
+ */
+static inline void scmi_discard_bad_evt_payload(struct kfifo *kq,
+						const unsigned int count)
+{
+	int i = 0;
+
+	pr_warn("SCMI Notification WQ :: skipping bad EVT Payload - %d bytes\n",
+		count);
+	/* Discard stale pending queued payload. */
+	for (i = 0; i < count; i++)
+		kfifo_skip(kq);
+}
+
+/**
+ * scmi_lookup_and_call_event_chain  - Lookup the proper chain and call it
+ *
+ * @evt_key: The event 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(u32 evt_key, void *report)
+{
+	int ret;
+	struct scmi_event_handler *hndl;
+
+	hndl = scmi_get_event_handler(evt_key);
+	if (IS_ERR_OR_NULL(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_event_handler(hndl);
+}
+
+/**
+ * scmi_events_dispatcher  - Common worker logic for all work items.
+ *
+ * In turn:
+ *  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 protocol can process their dedicated queues concurrently
+ *     (since scmi_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 (needed for lock-less access)
+ *
+ * @work: The work item to use, which is associated to the proper events_queue
+ */
+static void scmi_events_dispatcher(struct work_struct *work)
+{
+	struct events_queue *equeue;
+	struct scmi_event_header eh;
+
+	equeue = container_of(work, struct events_queue, notify_work);
+	while (kfifo_out(&equeue->kfifo, &eh, sizeof(eh))) {
+		u32 src_id, evt_key;
+		unsigned int outs;
+		struct scmi_registered_event *r_evt;
+		void *report = NULL;
+
+		evt_key = MAKE_EVT_KEY(eh.proto_id, eh.evt_id, NULL);
+		r_evt = idr_find(&scmi_registered_events, evt_key);
+		if (!r_evt) {
+			scmi_discard_bad_evt_payload(&equeue->kfifo,
+						     eh.payld_sz);
+			continue;
+		}
+
+		outs = kfifo_out(&equeue->kfifo, r_evt->scratch_bh,
+				 eh.payld_sz);
+		if (outs != eh.payld_sz) {
+			pr_warn("SCMI Notification WQ :: SKIP corrupted EVT Payload.\n");
+			continue;
+		}
+
+		/* Reset and fill custom report */
+		memset(r_evt->report, 0x00, r_evt->evt->max_report_sz);
+		report = r_evt->proto->ops->fill_custom_report(eh.evt_id,
+							eh.timestamp,
+							r_evt->scratch_bh,
+							eh.payld_sz,
+							r_evt->report,
+							&src_id);
+		if (!report)
+			continue;
+
+		/* At first search for a generic ALL src_ids handler... */
+		scmi_lookup_and_call_event_chain(evt_key, report);
+		if (src_id != SCMI_ALL_SRC_IDS) {
+			u32 *__sub_p = &src_id;
+
+			evt_key = MAKE_EVT_KEY(eh.proto_id, eh.evt_id, __sub_p);
+			scmi_lookup_and_call_event_chain(evt_key, report);
+		}
+	}
+}
+
+/**
+ * scmi_notify  - Queues a notification for further deferred processing
+ *
+ * This is called in interrupt context to queue a received event for
+ * deferred processing.
+ *
+ * @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)
+ *
+ * Return: 0 on Success
+ */
+int scmi_notify(u8 proto_id, u8 evt_id, const void *buf, size_t len, u64 ts)
+{
+	struct scmi_registered_event *r_evt;
+	struct scmi_event_header *eh;
+
+	if (unlikely(!scmi_notifications_initialized))
+		return 0;
+
+	r_evt = idr_find(&scmi_registered_events,
+			 MAKE_EVT_KEY(proto_id, evt_id, NULL));
+	if (unlikely(!r_evt || !r_evt->proto->equeue))
+		return -EINVAL;
+
+	if (unlikely(len > r_evt->evt->max_payld_sz)) {
+		pr_err("SCMI Notification discard badly sized message\n");
+		return -EINVAL;
+	}
+	if (unlikely(kfifo_avail(&r_evt->proto->equeue->kfifo) <
+		     sizeof(*eh) + len)) {
+		pr_warn("SCMI Notification queue full: dropping proto_id:%d  evt_id:%d  ts:%lld\n",
+			proto_id, evt_id, ts);
+		return -ENOMEM;
+	}
+
+	/*
+	 * Note that we can use the per protocol kfifo in a lock-less manner
+	 * since we have only one concurrent reader and writer but, in order
+	 * to avoid any trouble on the reader side, here we perform one single
+	 * write, so we have to collate event header and payload in a scratch
+	 * area at first.
+	 */
+	eh = r_evt->scratch_isr;
+	eh->timestamp = ts;
+	eh->proto_id = proto_id;
+	eh->evt_id = evt_id;
+	eh->payld_sz = len;
+	memcpy(eh->payld, buf, eh->payld_sz);
+	kfifo_in(&r_evt->proto->equeue->kfifo, eh, sizeof(*eh) + eh->payld_sz);
+	queue_work(r_evt->proto->equeue->wq,
+		   &r_evt->proto->equeue->notify_work);
+
+	return 0;
+}
+
+/**
+ * scmi_allocate_events_queue  - Allocate an events_queue descriptor
+ *
+ * @sz: Size of the kfifo to initialize
+ *
+ * Return: A valid pointer to the allocated events_queue on Success
+ */
+static struct events_queue *scmi_allocate_events_queue(size_t sz)
+{
+	int ret;
+	struct events_queue *equeue;
+
+	equeue = kzalloc(sizeof(*equeue), GFP_KERNEL);
+	if (!equeue)
+		return ERR_PTR(-ENOMEM);
+	ret = kfifo_alloc(&equeue->kfifo, sz, GFP_KERNEL);
+	if (ret) {
+		kfree(equeue);
+		return ERR_PTR(ret);
+	}
+	equeue->sz = sz;
+	INIT_WORK(&equeue->notify_work, scmi_events_dispatcher);
+	equeue->wq = scmi_notify_wq;
+
+	return equeue;
+}
+
+/**
+ * scmi_deallocate_events_queue  - Deallocate am events_queue descriptor
+ *
+ * @equeue: The events_queue to free
+ */
+static void scmi_deallocate_events_queue(struct events_queue *equeue)
+{
+	kfifo_free(&equeue->kfifo);
+	kfree(equeue);
+}
+
+/**
+ * scmi_allocate_registered_protocol_desc  - Allocate a registered protocol
+ * events' descriptor
+ *
+ * Used to keep protocol specific information related to events handling for any
+ * protocl which has registered at least one event.
+ *
+ * @proto_id: Protocol ID
+ * @queue_sz: Size of the associated queue to allocate
+ * @ops: Pointer to a struct holding references to protocol specific helpers
+ *	 needed during events handling
+ */
+static struct scmi_registered_protocol_events_desc *
+scmi_allocate_registered_protocol_desc(u8 proto_id, size_t queue_sz,
+				const struct scmi_protocol_event_ops *ops)
+{
+	int ret;
+	struct scmi_registered_protocol_events_desc *pdesc;
+
+	pdesc = idr_find(&scmi_registered_protocols, proto_id);
+	if (pdesc)
+		return pdesc;
+
+	pdesc = kzalloc(sizeof(*pdesc), GFP_KERNEL);
+	if (!pdesc)
+		return ERR_PTR(-ENOMEM);
+	pdesc->id = proto_id;
+	pdesc->ops = ops;
+
+	pdesc->equeue = scmi_allocate_events_queue(queue_sz);
+	if (IS_ERR(pdesc->equeue)) {
+		kfree(pdesc);
+		return ERR_CAST(pdesc->equeue);
+	}
+
+	ret = idr_alloc(&scmi_registered_protocols, pdesc,
+			pdesc->id, pdesc->id + 1, GFP_KERNEL);
+	if (ret < 0) {
+		pr_err("SCMI Failed to allocate PDESC IDR - key:%d - err:%d\n",
+		       pdesc->id, ret);
+		scmi_deallocate_events_queue(pdesc->equeue);
+		kfree(pdesc);
+		return ERR_PTR(ret);
+	}
+
+	return pdesc;
+}
+
+/**
+ * scmi_register_protocol_events  - Register Protocol Events with the core
+ *
+ * Used by SCMI Protocols initialization code to register with the notification
+ * core the list of supported events and their description: this takes care to
+ * pre-allocate all needed scratch buffers and link the proper event queue to
+ * this event.
+ *
+ * @proto_id: Protocol ID
+ * @queue_sz: Size in bytes of the associated queue to be allocated
+ * @ops: Protocol specific event-related operations
+ * @evt: Event descriptor array
+ * @num_events: Number of events in @evt array
+ *
+ * Return: 0 on Success
+ */
+int scmi_register_protocol_events(u8 proto_id, size_t queue_sz,
+				  const struct scmi_protocol_event_ops *ops,
+				  const struct scmi_event *evt, int num_events)
+{
+	int i;
+	struct scmi_registered_protocol_events_desc *pdesc;
+
+	if (!scmi_notifications_initialized)
+		return -EAGAIN;
+
+	if (!ops || !evt)
+		return -EINVAL;
+
+	pdesc = scmi_allocate_registered_protocol_desc(proto_id, queue_sz, ops);
+	if (IS_ERR(pdesc))
+		return -ENOMEM;
+
+	for (i = 0; i < num_events; i++, evt++) {
+		int ret;
+		u32 key;
+		struct scmi_registered_event *r_evt;
+
+		r_evt = kzalloc(sizeof(*r_evt), GFP_KERNEL);
+		if (!r_evt)
+			continue;
+		r_evt->proto = pdesc;
+		r_evt->evt = evt;
+
+		r_evt->scratch_isr = kzalloc(sizeof(struct scmi_event_header) +
+					     evt->max_payld_sz, GFP_KERNEL);
+		if (!r_evt->scratch_isr)
+			goto continue_isr_fail;
+
+		r_evt->scratch_bh = kzalloc(evt->max_payld_sz, GFP_KERNEL);
+		if (!r_evt->scratch_bh)
+			goto continue_bh_fail;
+
+		r_evt->report = kzalloc(evt->max_report_sz, GFP_KERNEL);
+		if (!r_evt->report)
+			goto continue_report_fail;
+
+		key = MAKE_EVT_KEY(r_evt->proto->id, evt->evt_id, NULL);
+		ret = idr_alloc(&scmi_registered_events, r_evt,
+				key, key + 1, GFP_KERNEL);
+		if (ret < 0) {
+			pr_err("SCMI Failed to allocate EVENT IDR - key:%X - err:%d\n",
+			       key, ret);
+			goto continue_idr_fail;
+		}
+
+		pr_info("SCMI Notification registered event - key:%X\n", key);
+		continue;
+
+	/* yes, this is not nice ... */
+continue_idr_fail:
+		kfree(r_evt->report);
+continue_report_fail:
+		kfree(r_evt->scratch_bh);
+continue_bh_fail:
+		kfree(r_evt->scratch_isr);
+continue_isr_fail:
+		kfree(r_evt);
+	}
+
+	return 0;
+}
+
+/**
+ * scmi_register_event_handler  - Allocate an Event handler
+ *
+ * Allocate an event handler and related notification chain associated with
+ * the event identified by the provided event key. Fails if the associated
+ * event is unknown to the core (i.e. it had not been successfully registered
+ * upfront by some protocol)
+ *
+ * @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_register_event_handler(u32 evt_key)
+{
+	int id;
+	u8 proto_id, evt_id;
+	struct scmi_registered_event *r_evt;
+	struct scmi_event_handler *hndl;
+
+	proto_id = KEY_XTRACT_PROTO_ID(evt_key);
+	evt_id = KEY_XTRACT_EVT_ID(evt_key);
+	r_evt = idr_find(&scmi_registered_events,
+			 MAKE_EVT_KEY(proto_id, evt_id, NULL));
+	if (!r_evt)
+		return ERR_PTR(-EINVAL);
+
+	hndl = kzalloc(sizeof(*hndl), GFP_KERNEL);
+	if (!hndl)
+		return ERR_PTR(-ENOMEM);
+	hndl->r_evt = r_evt;
+	hndl->evt_key = evt_key;
+	BLOCKING_INIT_NOTIFIER_HEAD(&hndl->chain);
+	refcount_set(&hndl->users, 1);
+
+	/* Register freshly allocated event handler */
+	id = idr_alloc(&scmi_registered_events_handlers, hndl,
+		       evt_key, evt_key + 1, GFP_KERNEL);
+	if (id < 0) {
+		pr_err("SCMI Failed to allocate HNDL IDR - key:%X  err:%d\n",
+		       evt_key, id);
+		kfree(hndl);
+		return ERR_PTR(id);
+	}
+
+	return hndl;
+}
+
+/**
+ * scmi_unregister_event_handler  - Free the provided Event handler
+ *
+ * @hndl: The event handler structure to free
+ */
+static void scmi_unregister_event_handler(struct scmi_event_handler *hndl)
+{
+	idr_remove(&scmi_registered_events_handlers, hndl->evt_key);
+	kfree(hndl);
+}
+
+/**
+ * __scmi_event_handler_get_ops  - Get or create an event handler
+ *
+ * After having got exclusive access to the registered events map, searches for
+ * the desired handler matching the key: when found adjust refcount, when not
+ * create and register a new handler is asked to do so.
+ * Events generation is NOT enabled within this routine since at creation time
+ * we usually want to have all setup and registered before events starts
+ * flowing.
+ *
+ * @evt_key: The event key to use
+ * @create: A boolean flag to specify if a handler must be created
+ *	    when not found
+ */
+static inline struct scmi_event_handler *
+__scmi_event_handler_get_ops(u32 evt_key, bool create)
+{
+	struct scmi_event_handler *hndl = NULL;
+
+	mutex_lock(&scmi_registered_events_handler_mtx);
+	hndl = idr_find(&scmi_registered_events_handlers, evt_key);
+	if (hndl)
+		refcount_inc(&hndl->users);
+	else if (create)
+		hndl = scmi_register_event_handler(evt_key);
+	mutex_unlock(&scmi_registered_events_handler_mtx);
+
+	return hndl;
+}
+
+static struct scmi_event_handler *scmi_get_event_handler(u32 evt_key)
+{
+	return __scmi_event_handler_get_ops(evt_key, false);
+}
+
+static struct scmi_event_handler *scmi_get_or_create_event_handler(u32 evt_key)
+{
+	return __scmi_event_handler_get_ops(evt_key, true);
+}
+
+/**
+ * __scmi_enable_events_ops  - Enable/disable events generation
+ *
+ * @hndl: The handler specifying the events enable/disable
+ * @action: The action to perform: true->Enable false->Disable
+ *
+ * Return: True when the required @action has been successfully executed
+ */
+static inline bool __scmi_enable_events_ops(struct scmi_event_handler *hndl,
+					    bool action)
+{
+	bool ret = true;
+
+	if (hndl->enabled != action) {
+		u8 evt_id;
+		u32 src_id;
+
+		evt_id = KEY_XTRACT_EVT_ID(hndl->evt_key);
+		src_id = KEY_XTRACT_SRC_ID(hndl->evt_key);
+		ret = hndl->r_evt->proto->ops->set_notify_enabled(evt_id,
+			      src_id != SCMI_ALL_SRC_IDS ? &src_id : NULL,
+			      action);
+		if (ret)
+			hndl->enabled = action;
+	}
+
+	return ret;
+}
+
+static bool scmi_enable_events(struct scmi_event_handler *hndl)
+{
+	return __scmi_enable_events_ops(hndl, true);
+}
+
+static bool scmi_disable_events(struct scmi_event_handler *hndl)
+{
+	return __scmi_enable_events_ops(hndl, false);
+}
+
+/**
+ * scmi_put_event_handler  - Put an event handler
+ *
+ * After having got exclusive access to the registered events map, update
+ * the refcount and if @hndl is no more in use by anyone:
+ *  - disable the events generation
+ *  - unregister and free the handler itself
+ *
+ * @hndl: The handler to act upon
+ */
+static void scmi_put_event_handler(struct scmi_event_handler *hndl)
+{
+	mutex_lock(&scmi_registered_events_handler_mtx);
+	if (refcount_dec_and_test(&hndl->users)) {
+		scmi_disable_events(hndl);
+		scmi_unregister_event_handler(hndl);
+	}
+	mutex_unlock(&scmi_registered_events_handler_mtx);
+}
+
+/**
+ * scmi_register_event_notifier  - Register a notifier_block for an event
+ *
+ * Generic helper to register a notifier_block attached to 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 os 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: in these cases @nb will be attached to a generic
+ * notification chain defined for ALL src_id of that proto_id/evt_id pair like:
+ *
+ *	(proto_X, evt_Y, NULL) --> chain_X_Y_ALL
+ *
+ * Any received event will be then dispatched to both such chains if at least
+ * one user had registered an @nb on them.
+ *
+ * Note also that notification chains are created dynamically: a new chain is
+ * created each time a new distinct tuple is detected and then the provided @nb
+ * is bound to such chain; at creation time the related SCMI notifications are
+ * also enabled: this way, only when at least one user has registered its
+ * interest for a specific event tuple, the underlying notification chain is
+ * created and the related notifications are enabled in the platform.
+ *
+ * @proto_id: Protocol ID
+ * @evt_id: Event ID
+ * @src_id: Source ID
+ * @nb: A standard notifier block to register for the specified event
+ *
+ * Return: Return 0 on Success
+ */
+int scmi_register_event_notifier(u8 proto_id, u8 evt_id, u32 *src_id,
+				 struct notifier_block *nb)
+{
+	u32 evt_key;
+	struct scmi_event_handler *hndl;
+
+	evt_key = MAKE_EVT_KEY(proto_id, evt_id, src_id);
+	hndl = scmi_get_or_create_event_handler(evt_key);
+	if (IS_ERR_OR_NULL(hndl))
+		return PTR_ERR(hndl);
+
+	blocking_notifier_chain_register(&hndl->chain, nb);
+
+	if (!scmi_enable_events(hndl)) {
+		pr_err("SCMI Failed to ENABLE events for key:%X !\n", evt_key);
+		blocking_notifier_chain_unregister(&hndl->chain, nb);
+		scmi_put_event_handler(hndl);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/**
+ * scmi_unregister_event_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.
+ *
+ * @proto_id: Protocol ID
+ * @evt_id: Event ID
+ * @src_id: Source ID
+ * @nb: The notifier_block to unregister
+ *
+ * Return: 0 on Success
+ */
+int scmi_unregister_event_notifier(u8 proto_id, u8 evt_id, u32 *src_id,
+				   struct notifier_block *nb)
+{
+	u32 evt_key;
+	struct scmi_event_handler *hndl;
+
+	evt_key = MAKE_EVT_KEY(proto_id, evt_id, src_id);
+	hndl = scmi_get_event_handler(evt_key);
+	if (IS_ERR_OR_NULL(hndl))
+		return -EINVAL;
+
+	blocking_notifier_chain_unregister(&hndl->chain, nb);
+
+	scmi_put_event_handler(hndl);
+	/*
+	 * If this was the last user callback for this handler, this last put
+	 * will force the handler to be freed.
+	 * Note that if a call_chain walk is ongoing it will be the call_chain
+	 * put request which will finally free the handler; note also that any
+	 * operation on the inner notifier_block chain is protected on its own.
+	 */
+	scmi_put_event_handler(hndl);
+
+	return 0;
+}
+
+/**
+ * scmi_notification_init  - Initializes Notification Core Support
+ *
+ * Return: 0 on Success
+ */
+int __init scmi_notification_init(void)
+{
+	scmi_notify_wq = alloc_workqueue("scmi_notify",
+					 WQ_UNBOUND | WQ_FREEZABLE,
+					 SCMI_NOTIF_MAX_ACTIVE_QUEUES);
+	if (!scmi_notify_wq)
+		return -ENOMEM;
+	idr_init(&scmi_registered_events);
+	idr_init(&scmi_registered_events_handlers);
+	idr_init(&scmi_registered_protocols);
+
+	scmi_notifications_initialized = true;
+
+	pr_info("SCMI Notifications enabled.\n");
+
+	return 0;
+}
+
+/**
+ * scmi_notification_exit  - Shutdown and clean Notification core
+ */
+void __exit scmi_notification_exit(void)
+{
+	int k;
+	struct scmi_event_handler *hndl;
+	struct scmi_registered_protocol_events_desc *pdesc;
+	struct scmi_registered_event *r_evt;
+
+	scmi_notifications_initialized = false;
+
+	/* Disable notifications' generation */
+	idr_for_each_entry(&scmi_registered_events_handlers, hndl, k)
+		scmi_disable_events(hndl);
+
+	/* Let pending work complete */
+	destroy_workqueue(scmi_notify_wq);
+
+	/* Remove ALL events handlers */
+	idr_for_each_entry(&scmi_registered_events_handlers, hndl, k)
+		scmi_put_event_handler(hndl);
+	idr_destroy(&scmi_registered_events_handlers);
+
+	/* Finally remove all registered events */
+	idr_for_each_entry(&scmi_registered_events, r_evt, k) {
+		idr_remove(&scmi_registered_events, k);
+		kfree(r_evt->report);
+		kfree(r_evt->scratch_isr);
+		kfree(r_evt->scratch_bh);
+		kfree(r_evt);
+	}
+	idr_destroy(&scmi_registered_events);
+
+	/* free any remaining protocol data */
+	idr_for_each_entry(&scmi_registered_protocols, pdesc, k) {
+		idr_remove(&scmi_registered_protocols, k);
+		scmi_deallocate_events_queue(pdesc->equeue);
+		kfree(pdesc);
+	}
+	idr_destroy(&scmi_registered_protocols);
+}
diff --git a/drivers/firmware/arm_scmi/notify.h b/drivers/firmware/arm_scmi/notify.h
new file mode 100644
index 000000000000..6fa07b244b14
--- /dev/null
+++ b/drivers/firmware/arm_scmi/notify.h
@@ -0,0 +1,79 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * System Control and Management Interface (SCMI) Message Protocol
+ * notification header file containing some definitions, structures
+ * and function prototypes related to SCMI Notification handling.
+ *
+ * Copyright (C) 2019 ARM Ltd.
+ */
+#ifndef _SCMI_NOTIFY_H
+#define _SCMI_NOTIFY_H
+
+#include <linux/bug.h>
+#include <linux/notifier.h>
+#include <linux/types.h>
+
+#define	SCMI_ALL_SRC_IDS		0x0000ffffL
+
+#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
+ *
+ * Each SCMI protocol, during its initialization phase, can describe the events
+ * it wishes to support in a few struct scmi_event and pass them to the core
+ * using scmi_register_protocol_events().
+ *
+ * @evt_id: Event ID
+ * @max_payld_sz: Max possible size for the payload of a notif msg of this kind
+ * @max_report_sz: Max possible size for the report of a notif msg of this kind
+ */
+struct scmi_event {
+	u8	evt_id;
+	size_t	max_payld_sz;
+	size_t	max_report_sz;
+
+};
+
+/**
+ * scmi_protocol_event_ops  - Helpers called by notification core.
+ *
+ * These are called only in process context.
+ *
+ * @set_notify_enabled: Enable/disable the required evt_id/src_id notifications
+ *			using the proper custom protocol commands.
+ *			Return true if at least one the required src_id
+ *			has been successfully enabled/disabled
+ * @fill_custom_report: fills a custom event report from the provided
+ *			event message payld identifying the event
+ *			specific src_id.
+ *			Return NULL on failure otherwise @report now fully
+ *			populated
+ */
+struct scmi_protocol_event_ops {
+	bool (*set_notify_enabled)(u8 evt_id, const u32 *src_id, bool enabled);
+	void *(*fill_custom_report)(u8 evt_id, u64 timestamp, const void *payld,
+				    size_t payld_sz, void *report, u32 *src_id);
+};
+
+int scmi_notification_init(void);
+void scmi_notification_exit(void);
+int scmi_register_protocol_events(u8 proto_id, size_t queue_sz,
+				  const struct scmi_protocol_event_ops *ops,
+				  const struct scmi_event *evt, int num_events);
+int scmi_register_event_notifier(u8 proto_id, u8 evt_id, u32 *sub_id,
+				 struct notifier_block *nb);
+int scmi_unregister_event_notifier(u8 proto_id, u8 evt_id, u32 *sub_id,
+				   struct notifier_block *nb);
+int scmi_notify(u8 proto_id, u8 evt_id, const void *buf, size_t len, u64 ts);
+
+#endif /* _SCMI_NOTIFY_H */
-- 
2.17.1