platform/surface: aggregator: Allow registering notifiers without enabling events

Currently, each SSAM event notifier is directly tied to one group of
events. This makes sense as registering a notifier will automatically
take care of enabling the corresponding event group and normally drivers
only need notifications for a very limited number of events, associated
with different callbacks for each group.

However, there are rare cases, especially for debugging, when we want to
get notifications for a whole event target category instead of just a
single group of events in that category. Registering multiple notifiers,
i.e. one per group, may be infeasible due to two issues: a) we might not
know every event enable/disable specification as some events are
auto-enabled by the EC and b) forwarding this to the same callback will
lead to duplicate events as we might not know the full event
specification to perform the appropriate filtering.

This commit introduces observer-notifiers, which are notifiers that are
not tied to a specific event group and do not attempt to manage any
events. In other words, they can be registered without enabling any
event group or incrementing the corresponding reference count and just
act as silent observers, listening to all currently/previously enabled
events based on their match-specification.

Essentially, this allows us to register one single notifier for a full
event target category, meaning that we can process all events of that
target category in a single callback without duplication. Specifically,
this will be used in the cdev debug interface to forward events to
user-space via a device file from which the events can be read.

Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20210604134755.535590-2-luzmaximilian@gmail.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/linux/surface_aggregator/controller.h b/include/linux/surface_aggregator/controller.h
index 0806796eabcb..cf4bb48a850e 100644
--- a/include/linux/surface_aggregator/controller.h
+++ b/include/linux/surface_aggregator/controller.h
@@ -796,6 +796,20 @@ enum ssam_event_mask {
 	SSAM_EVENT_REGISTRY(SSAM_SSH_TC_REG, 0x02, 0x01, 0x02)
 
 /**
+ * enum ssam_event_notifier_flags - Flags for event notifiers.
+ * @SSAM_EVENT_NOTIFIER_OBSERVER:
+ *	The corresponding notifier acts as observer. Registering a notifier
+ *	with this flag set will not attempt to enable any event. Equally,
+ *	unregistering will not attempt to disable any event. Note that a
+ *	notifier with this flag may not even correspond to a certain event at
+ *	all, only to a specific event target category. Event matching will not
+ *	be influenced by this flag.
+ */
+enum ssam_event_notifier_flags {
+	SSAM_EVENT_NOTIFIER_OBSERVER = BIT(0),
+};
+
+/**
  * struct ssam_event_notifier - Notifier block for SSAM events.
  * @base:        The base notifier block with callback function and priority.
  * @event:       The event for which this block will receive notifications.
@@ -803,6 +817,7 @@ enum ssam_event_mask {
  * @event.id:    ID specifying the event.
  * @event.mask:  Flags determining how events are matched to the notifier.
  * @event.flags: Flags used for enabling the event.
+ * @flags:       Notifier flags (see &enum ssam_event_notifier_flags).
  */
 struct ssam_event_notifier {
 	struct ssam_notifier_block base;
@@ -813,6 +828,8 @@ struct ssam_event_notifier {
 		enum ssam_event_mask mask;
 		u8 flags;
 	} event;
+
+	unsigned long flags;
 };
 
 int ssam_notifier_register(struct ssam_controller *ctrl,