firmware: arm_scmi: Check for notification support

When registering protocol events, use the optional .is_notify_supported
callback provided by the protocol to check if that specific notification
type is available for that particular resource on the running system,
marking it as unsupported otherwise.

Then, when a notification enable request is received, return an error if
it was previously marked as unsuppported, so avoiding to send a needless
notification enable command and check the returned value for failure.

Signed-off-by: Cristian Marussi <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Sudeep Holla <[e-mail]>

drivers/firmware/arm_scmi/notify.c

···
 #define PROTO_ID_MASK		GENMASK(31, 24)
 #define EVT_ID_MASK		GENMASK(23, 16)
 #define SRC_ID_MASK		GENMASK(15, 0)
+#define NOTIF_UNSUPP		-1
 
 /*
  * Builds an unsigned 32bit key from the given input tuple to be used
···
 
 	pd->ph = ph;
 	for (i = 0; i < ee->num_events; i++, evt++) {
+		int id;
 		struct scmi_registered_event *r_evt;
 
 		r_evt = devm_kzalloc(ni->handle->dev, sizeof(*r_evt),
···
 					     evt->max_report_sz, GFP_KERNEL);
 		if (!r_evt->report)
 			return -ENOMEM;
+
+		for (id = 0; id < r_evt->num_sources; id++)
+			if (ee->ops->is_notify_supported &&
+			    !ee->ops->is_notify_supported(ph, r_evt->evt->id, id))
+				refcount_set(&r_evt->sources[id], NOTIF_UNSUPP);
 
 		pd->registered_events[i] = r_evt;
 		/* Ensure events are updated */
···
 			int ret = 0;
 
 			sid = &r_evt->sources[src_id];
-			if (refcount_read(sid) == 0) {
+			if (refcount_read(sid) == NOTIF_UNSUPP) {
+				dev_dbg(r_evt->proto->ph->dev,
+					"Notification NOT supported - proto_id:%d  evt_id:%d  src_id:%d",
+					r_evt->proto->id, r_evt->evt->id,
+					src_id);
+				ret = -EOPNOTSUPP;
+			} else if (refcount_read(sid) == 0) {
 				ret = REVT_NOTIFY_ENABLE(r_evt, r_evt->evt->id,
 							 src_id);
 				if (!ret)
···
 	} else {
 		for (; num_sources; src_id++, num_sources--) {
 			sid = &r_evt->sources[src_id];
+			if (refcount_read(sid) == NOTIF_UNSUPP)
+				continue;
 			if (refcount_dec_and_test(sid))
 				REVT_NOTIFY_DISABLE(r_evt,
 						    r_evt->evt->id, src_id);

drivers/firmware/arm_scmi/notify.h

···
 
 /**
  * struct scmi_event_ops  - Protocol helpers called by the notification core.
+ * @is_notify_supported: Return 0 if the specified notification for the
+ *			 specified resource (src_id) is supported.
  * @get_num_sources: Returns the number of possible events' sources for this
  *		     protocol
  * @set_notify_enabled: Enable/disable the required evt_id/src_id notifications
···
  *	    process context.
  */
 struct scmi_event_ops {
+	bool (*is_notify_supported)(const struct scmi_protocol_handle *ph,
+				    u8 evt_id, u32 src_id);
 	int (*get_num_sources)(const struct scmi_protocol_handle *ph);
 	int (*set_notify_enabled)(const struct scmi_protocol_handle *ph,
 				  u8 evt_id, u32 src_id, bool enabled);