[media] v4l: events: Define V4L2_EVENT_FRAME_SYNC

Define a frame sync event to tell user space when the reception of a frame
starts.

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml b/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml
index 275be9689d88..5c70b616d818 100644
--- a/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml
@@ -139,6 +139,22 @@
             </entry>
           </row>
           <row>
+            <entry><constant>V4L2_EVENT_FRAME_SYNC</constant></entry>
+            <entry>4</entry>
+            <entry>
+              <para>Triggered immediately when the reception of a
+              frame has begun. This event has a
+              &v4l2-event-frame-sync; associated with it.</para>
+
+              <para>If the hardware needs to be stopped in the case of a
+              buffer underrun it might not be able to generate this event.
+              In such cases the <structfield>frame_sequence</structfield>
+              field in &v4l2-event-frame-sync; will not be incremented. This
+              causes two consecutive frame sequence numbers to have n times
+              frame interval in between them.</para>
+            </entry>
+          </row>
+          <row>
             <entry><constant>V4L2_EVENT_PRIVATE_START</constant></entry>
             <entry>0x08000000</entry>
             <entry>Base event number for driver-private events.</entry>