V4L/DVB: V4L: Events: Add documentation
Add documentation on how to use V4L2 events, both for V4L2 drivers and for
V4L2 applications.
Signed-off-by: Sakari Ailus <sakari.ailus@maxwell.research.nokia.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/Documentation/DocBook/v4l/dev-event.xml b/Documentation/DocBook/v4l/dev-event.xml
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+ <title>Event Interface</title>
+
+ <para>The V4L2 event interface provides means for user to get
+ immediately notified on certain conditions taking place on a device.
+ This might include start of frame or loss of signal events, for
+ example.
+ </para>
+
+ <para>To receive events, the events the user is interested in first must
+ be subscribed using the &VIDIOC-SUBSCRIBE-EVENT; ioctl. Once an event is
+ subscribed, the events of subscribed types are dequeueable using the
+ &VIDIOC-DQEVENT; ioctl. Events may be unsubscribed using
+ VIDIOC_UNSUBSCRIBE_EVENT ioctl. The special event type V4L2_EVENT_ALL may
+ be used to unsubscribe all the events the driver supports.</para>
+
+ <para>The event subscriptions and event queues are specific to file
+ handles. Subscribing an event on one file handle does not affect
+ other file handles.
+ </para>
+
+ <para>The information on dequeueable events is obtained by using select or
+ poll system calls on video devices. The V4L2 events use POLLPRI events on
+ poll system call and exceptions on select system call. </para>
+
+ <!--
+Local Variables:
+mode: sgml
+sgml-parent-document: "v4l2.sgml"
+indent-tabs-mode: nil
+End:
+ -->