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

Jonathan Cameron
2020-01-27T18:11:55Z

On Mon, 20 Jan 2020 12:23:26 +0000
Cristian Marussi <cristian.marussi@arm.com> wrote:

> 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>

I'm not keen on the huge asymmetry on the setup and tear down paths.
For instance the lack of a scmi_unregister_protocol events.

The idr usage is not standard. They aren't the right structure
if you known the value you want.

Not a particularly thorough review otherwise. Out of time for today and
may not get back to this for a while.

Thanks,

Jonathan

> ---
> 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)
> + *
No point in having blank lines at the end of a comment block.
> + *
> + */
> +
> +#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

Not valid kernel-doc. I'll assume all other instances will get fixed
and not bother talking about them.

> + *
> + * 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
scratch_bh.

> + * @report: A pre-allocated buffer used by the deferred workr to fill a

worker

> + * 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

That's not a good description.

> + *
> + * 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

function name is wrong.

> + *
> + * @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.

protocol

> + *
> + * @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);

Perhaps add a comment here on why this might get called multiple times
but is still safe from point of view of release path.

> + 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);

Umm. That's not using an idr for what it is meant for. You aren't allocating an id, you
are using it as a poor wrapper around an xarray.

> + 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

so

> + * 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.

both should be all I think.

> + *
> + * 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.

That's one of the most complex bits of punctuation I've seenin a comment for
a long time. Please break that sentence up for readability.

> + *
> + * @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 */

Finally seems a bit premature here ;)

> + 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

I don't think this is valid kernel-doc. Make sure to point the scripts at the
file and check and fix any warnings.

> + *
> + * 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

Nitpick. Inconsistent capitalization after the :

> + * 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 */