driver-api/media/v4l2-event.rst

9 Events are subscribed per-filehandle. An event specification consists of a
11 ``id`` field. If unused, then the ``id`` is 0. So an event is uniquely
17 When the user subscribes to an event, a :c:type:`v4l2_subscribed_event`
19 subscribed event.
26 So every ``(type, ID)`` event tuple will have its own
32 :c:type:`v4l2_kevent` ringbuffer, then the oldest event will be dropped
37 know which event to dequeue first.
39 Finally, if the event subscription is associated with a particular object
41 so that an event can be raised by that object. So the ``node`` field can
56   event to that object.
60 callbacks are called when a new event is raised and there is no more room.
62 The ``replace()`` callback allows you to replace the payload of the old event
63 with that of the new event, merging any relevant data from the old payload
64 into the new payload that replaces it. It is called when this event type has
65 a ringbuffer with size is one, i.e. only one event can be stored in the
68 The ``merge()`` callback allows you to merge the oldest event payload into
69 that of the second-oldest event payload. It is called when
75 A good example of these ``replace``/``merge`` callbacks is in v4l2-event.c:
76 ``ctrls_replace()`` and ``ctrls_merge()`` callbacks for the control event.
93 Subscribing to an event is via:
103 with specified event id, and then should call
104 :c:func:`v4l2_event_subscribe` to subscribe the event.
106 The elems argument is the size of the event queue for this event. If it is 0,
107 then the framework will fill in a default value (this depends on the event
118 	 event twice will only cause this callback to get called once)
120 replace  replace event 'old' with event 'new'.
121 merge    merge event 'old' into event 'new'.
127 Unsubscribing an event
130 Unsubscribing to an event is via:
143 Check if there's a pending event
146 Checking if there's a pending event is via:
163 smallest available event type. The drivers must allocate their events from
166 The first event type in the class is reserved for future use, so the first
167 available event type is 'class base + 1'.
172 A subdev can directly send an event to the :c:type:`v4l2_device` notify
174 the subdev that sends the event to the video node(s) associated with the
175 subdev that need to be informed about such an event.
177 V4L2 event functions and data structures
180 .. kernel-doc:: include/media/v4l2-event.h