firmware: arm_scmi: Make notifications aware of protocols users

Account for any active registered notifier against the proper related
protocol, do not consider pending event handlers, only active handlers
will concur to protocol usage accounting.

Link: https://lore.kernel.org/r/20210316124903.35011-5-cristian.marussi@arm.com
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

1 files changed, 44 insertions, 7 deletions

diff --git a/drivers/firmware/arm_scmi/notify.c b/drivers/firmware/arm_scmi/notify.c
index 66196b293b6c..09015f1f9942 100644
--- a/drivers/firmware/arm_scmi/notify.c
+++ b/drivers/firmware/arm_scmi/notify.c
@@ -91,6 +91,7 @@
 #include <linux/types.h>
 #include <linux/workqueue.h>
 
+#include "common.h"
 #include "notify.h"
 
 #define SCMI_MAX_PROTO		256
@@ -368,7 +369,7 @@ static struct scmi_event_handler *
 scmi_get_active_handler(struct scmi_notify_instance *ni, u32 evt_key);
 static void scmi_put_active_handler(struct scmi_notify_instance *ni,
 				    struct scmi_event_handler *hndl);
-static void scmi_put_handler_unlocked(struct scmi_notify_instance *ni,
+static bool scmi_put_handler_unlocked(struct scmi_notify_instance *ni,
 				      struct scmi_event_handler *hndl);
 
 /**
@@ -900,9 +901,21 @@ static inline int scmi_bind_event_handler(struct scmi_notify_instance *ni,
 	if (!r_evt)
 		return -EINVAL;
 
-	/* Remove from pending and insert into registered */
+	/*
+	 * Remove from pending and insert into registered while getting hold
+	 * of protocol instance.
+	 */
 	hash_del(&hndl->hash);
+	/*
+	 * Acquire protocols only for NON pending handlers, so as NOT to trigger
+	 * protocol initialization when a notifier is registered against a still
+	 * not registered protocol, since it would make little sense to force init
+	 * protocols for which still no SCMI driver user exists: they wouldn't
+	 * emit any event anyway till some SCMI driver starts using it.
+	 */
+	scmi_protocol_acquire(ni->handle, KEY_XTRACT_PROTO_ID(hndl->key));
 	hndl->r_evt = r_evt;
+
 	mutex_lock(&r_evt->proto->registered_mtx);
 	hash_add(r_evt->proto->registered_events_handlers,
 		 &hndl->hash, hndl->key);
@@ -1193,41 +1206,65 @@ static int scmi_disable_events(struct scmi_event_handler *hndl)
  * * unregister and free the handler itself
  *
  * Context: Assumes all the proper locking has been managed by the caller.
+ *
+ * Return: True if handler was freed (users dropped to zero)
  */
-static void scmi_put_handler_unlocked(struct scmi_notify_instance *ni,
+static bool scmi_put_handler_unlocked(struct scmi_notify_instance *ni,
 				      struct scmi_event_handler *hndl)
 {
+	bool freed = false;
+
 	if (refcount_dec_and_test(&hndl->users)) {
 		if (!IS_HNDL_PENDING(hndl))
 			scmi_disable_events(hndl);
 		scmi_free_event_handler(hndl);
+		freed = true;
 	}
+
+	return freed;
 }
 
 static void scmi_put_handler(struct scmi_notify_instance *ni,
 			     struct scmi_event_handler *hndl)
 {
+	bool freed;
+	u8 protocol_id;
 	struct scmi_registered_event *r_evt = hndl->r_evt;
 
 	mutex_lock(&ni->pending_mtx);
-	if (r_evt)
+	if (r_evt) {
+		protocol_id = r_evt->proto->id;
 		mutex_lock(&r_evt->proto->registered_mtx);
+	}
 
-	scmi_put_handler_unlocked(ni, hndl);
+	freed = scmi_put_handler_unlocked(ni, hndl);
 
-	if (r_evt)
+	if (r_evt) {
 		mutex_unlock(&r_evt->proto->registered_mtx);
+		/*
+		 * Only registered handler acquired protocol; must be here
+		 * released only AFTER unlocking registered_mtx, since
+		 * releasing a protocol can trigger its de-initialization
+		 * (ie. including r_evt and registered_mtx)
+		 */
+		if (freed)
+			scmi_protocol_release(ni->handle, protocol_id);
+	}
 	mutex_unlock(&ni->pending_mtx);
 }
 
 static void scmi_put_active_handler(struct scmi_notify_instance *ni,
 				    struct scmi_event_handler *hndl)
 {
+	bool freed;
 	struct scmi_registered_event *r_evt = hndl->r_evt;
+	u8 protocol_id = r_evt->proto->id;
 
 	mutex_lock(&r_evt->proto->registered_mtx);
-	scmi_put_handler_unlocked(ni, hndl);
+	freed = scmi_put_handler_unlocked(ni, hndl);
 	mutex_unlock(&r_evt->proto->registered_mtx);
+	if (freed)
+		scmi_protocol_release(ni->handle, protocol_id);
 }
 
 /**