[PATCH v11 13/25] firmware: arm-scmi: Add telemetry generic event support

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

Add support to allow SCMI driver users to subscribe/unsubscribe to specific
Telemetry  abstract (non protocol) events.

This enables SCMI drivers to subscribe to available events by registering
an eventfd context that the core SCMI stack will use as a signalling
mechanisms.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
v10 --> v11
 - move events cleanup into resource_free
v8 --> v9
 - add a TLM_EVT_DUMMY placeholder (waiting for more events later on..)
---
 drivers/firmware/arm_scmi/telemetry.c | 97 +++++++++++++++++++++++++++
 include/linux/scmi_protocol.h         | 16 +++++
 2 files changed, 113 insertions(+)

diff --git a/drivers/firmware/arm_scmi/telemetry.c b/drivers/firmware/arm_scmi/telemetry.c
index 6409ee727158..4bb2010c89b5 100644
--- a/drivers/firmware/arm_scmi/telemetry.c
+++ b/drivers/firmware/arm_scmi/telemetry.c
@@ -12,6 +12,7 @@
 #include <linux/completion.h>
 #include <linux/err.h>
 #include <linux/delay.h>
+#include <linux/eventfd.h>
 #include <linux/io.h>
 #include <linux/limits.h>
 #include <linux/minmax.h>
@@ -479,6 +480,11 @@ enum de_state {
 	ENA_MAX
 };
 
+struct telemetry_event {
+	struct eventfd_ctx *ctx;
+	struct list_head item;
+};
+
 struct telemetry_info {
 	bool streaming_mode;
 	unsigned int num_shmti;
@@ -505,6 +511,9 @@ struct telemetry_info {
 	struct list_head free_des;
 	struct list_head fcs_des;
 	struct scmi_telemetry_info info;
+	/* Mutex to protect access to @events */
+	struct mutex events_mtx;
+	struct list_head events[SCMI_TLM_EVT_MAX];
 	struct notifier_block telemetry_nb;
 	atomic_t rinfo_initializing;
 	struct completion rinfo_initdone;
@@ -524,6 +533,21 @@ static int scmi_telemetry_shmti_scan(struct telemetry_info *ti,
 static inline void scmi_telemetry_uuid_link(struct telemetry_de *tde,
 					    struct telemetry_uuid *uuid);
 
+static int scmi_telemetry_event_signal(struct telemetry_info *ti,
+				       enum scmi_telemetry_event type)
+{
+	struct telemetry_event *evt;
+
+	if (type >= SCMI_TLM_EVT_MAX)
+		return -EINVAL;
+
+	guard(mutex)(&ti->events_mtx);
+	list_for_each_entry(evt, &ti->events[type], item)
+		eventfd_signal(evt->ctx);
+
+	return 0;
+}
+
 static inline void
 scmi_telemetry_de_state_update(struct telemetry_info *ti, enum de_state state,
 			       bool *current_state, const bool next_state)
@@ -3330,6 +3354,54 @@ static int scmi_telemetry_reset(const struct scmi_protocol_handle *ph)
 	return ret;
 }
 
+static int scmi_telemetry_event_subscribe(const struct scmi_protocol_handle *ph,
+					  enum scmi_telemetry_event type,
+					  struct eventfd_ctx *ctx)
+{
+	struct telemetry_info *ti = ph->get_priv(ph);
+	struct telemetry_event *evt;
+
+	if (type >= SCMI_TLM_EVT_MAX)
+		return -EINVAL;
+
+	evt = kzalloc_obj(*evt);
+	if (!evt)
+		return -ENOMEM;
+
+	evt->ctx = ctx;
+	guard(mutex)(&ti->events_mtx);
+	list_add(&evt->item, &ti->events[type]);
+
+	trace_scmi_tlm_access(0, "TLM_EVT_SUBS", 0, 0);
+
+	return 0;
+}
+
+static int scmi_telemetry_event_unsubscribe(const struct scmi_protocol_handle *ph,
+					    enum scmi_telemetry_event type,
+					    struct eventfd_ctx *ctx)
+{
+	struct telemetry_info *ti = ph->get_priv(ph);
+	struct telemetry_event *evt, *n;
+
+	if (type >= SCMI_TLM_EVT_MAX)
+		return -EINVAL;
+
+	guard(mutex)(&ti->events_mtx);
+	list_for_each_entry_safe(evt, n, &ti->events[type], item) {
+		if (evt->ctx == ctx) {
+			list_del(&evt->item);
+			kfree(evt);
+
+			trace_scmi_tlm_access(0, "TLM_EVT_UNSUBS", 0, 0);
+
+			break;
+		}
+	}
+
+	return 0;
+}
+
 static const struct scmi_telemetry_proto_ops tlm_proto_ops = {
 	.info_get = scmi_telemetry_info_get,
 	.de_lookup = scmi_telemetry_de_lookup,
@@ -3341,6 +3413,8 @@ static const struct scmi_telemetry_proto_ops tlm_proto_ops = {
 	.des_bulk_read = scmi_telemetry_des_bulk_read,
 	.des_sample_get = scmi_telemetry_des_sample_get,
 	.reset = scmi_telemetry_reset,
+	.event_subscribe = scmi_telemetry_event_subscribe,
+	.event_unsubscribe = scmi_telemetry_event_unsubscribe,
 };
 
 static bool
@@ -3555,6 +3629,23 @@ __scmi_telemetry_resources_get(struct telemetry_info *ti)
 	return smp_load_acquire(&ti->rinfo);
 }
 
+static void scmi_telemetry_event_cleanup(struct telemetry_info *ti)
+{
+	guard(mutex)(&ti->events_mtx);
+	/* Clear any residual events */
+	for (int type = 0; type < SCMI_TLM_EVT_MAX; type++) {
+		struct telemetry_event *evt, *n;
+
+		list_for_each_entry_safe(evt, n, &ti->events[type], item) {
+			dev_warn(ti->ph->dev,
+				 "Found UN-SUBSCRIBED event type %d!\n", type);
+			list_del(&evt->item);
+			eventfd_ctx_put(evt->ctx);
+			kfree(evt);
+		}
+	}
+}
+
 static void scmi_telemetry_resources_free(void *arg)
 {
 	struct scmi_telemetry_res_info *rinfo;
@@ -3595,6 +3686,9 @@ static void scmi_telemetry_resources_free(void *arg)
 		scmi_telemetry_line_put(line);
 	xa_destroy(&ti->xa_lines);
 
+	/* Cleanup any still registered event */
+	scmi_telemetry_event_cleanup(ti);
+
 	kfree(ti->tdes);
 	kfree(rinfo->des);
 	kfree(rinfo->dei_store);
@@ -3750,6 +3844,9 @@ static int scmi_telemetry_instance_init(struct telemetry_info *ti)
 	if (ret)
 		return ret;
 
+	for (int i = 0; i < SCMI_TLM_EVT_MAX; i++)
+		INIT_LIST_HEAD(&ti->events[i]);
+	mutex_init(&ti->events_mtx);
 	atomic_set(&ti->des_enabled[ENA_STATE], 0);
 	atomic_set(&ti->des_enabled[ENA_TSTAMP], 0);
 	mutex_init(&ti->des_enabled_mtx);
diff --git a/include/linux/scmi_protocol.h b/include/linux/scmi_protocol.h
index 2d571c78613b..06591b27f365 100644
--- a/include/linux/scmi_protocol.h
+++ b/include/linux/scmi_protocol.h
@@ -11,6 +11,7 @@
 #include <linux/bitfield.h>
 #include <linux/bitops.h>
 #include <linux/device.h>
+#include <linux/eventfd.h>
 #include <linux/notifier.h>
 #include <linux/types.h>
 #include <linux/uuid.h>
@@ -994,6 +995,11 @@ struct scmi_telemetry_de_sample {
 	unsigned long long val;
 };
 
+enum scmi_telemetry_event {
+	SCMI_TLM_EVT_DUMMY,
+	SCMI_TLM_EVT_MAX,
+};
+
 /**
  * struct scmi_telemetry_proto_ops - represents the various operations provided
  *	by SCMI Telemetry Protocol
@@ -1017,6 +1023,10 @@ struct scmi_telemetry_de_sample {
  *		    This causes an immediate update platform-side of all the
  *		    enabled DEs.
  * @reset: reset configuration and telemetry data.
+ * @event_subscribe: subscribe to the specified event @type using the provided
+ *		     @eventfd_ctx.
+ * @event_unsubscribe: unsubscribe to the specified event @type the previously
+ *		       registered @eventfd_ctx.
  */
 struct scmi_telemetry_proto_ops {
 	const struct scmi_telemetry_info __must_check *(*info_get)
@@ -1044,6 +1054,12 @@ struct scmi_telemetry_proto_ops {
 	int __must_check (*des_sample_get)(const struct scmi_protocol_handle *ph,
 					   int grp_id, int *num_samples,
 					   struct scmi_telemetry_de_sample *samples);
+	int (*event_subscribe)(const struct scmi_protocol_handle *ph,
+			       enum scmi_telemetry_event type,
+			       struct eventfd_ctx *ctx);
+	int (*event_unsubscribe)(const struct scmi_protocol_handle *ph,
+				 enum scmi_telemetry_event type,
+				 struct eventfd_ctx *ctx);
 	int (*reset)(const struct scmi_protocol_handle *ph);
 };
 
-- 
2.54.0