[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>

Documentation/DocBook/media/v4l/vidioc-dqevent.xml

@@ -86,6 +86,12 @@
 	    <entry>Event data for event V4L2_EVENT_CTRL.
             </entry>
 	  </row>
+	  <row>
+	    <entry></entry>
+	    <entry>&v4l2-event-frame-sync;</entry>
+            <entry><structfield>frame</structfield></entry>
+	    <entry>Event data for event V4L2_EVENT_FRAME_SYNC.</entry>
+	  </row>
 	  <row>
 	    <entry></entry>
 	    <entry>__u8</entry>
@@ -220,6 +226,22 @@
       </tgroup>
     </table>
 
+    <table frame="none" pgwide="1" id="v4l2-event-frame-sync">
+      <title>struct <structname>v4l2_event_frame_sync</structname></title>
+      <tgroup cols="3">
+	&cs-str;
+	<tbody valign="top">
+	  <row>
+	    <entry>__u32</entry>
+	    <entry><structfield>frame_sequence</structfield></entry>
+	    <entry>
+	      The sequence number of the frame being received.
+	    </entry>
+	  </row>
+	</tbody>
+      </tgroup>
+    </table>
+
     <table pgwide="1" frame="none" id="changes-flags">
       <title>Changes</title>
       <tgroup cols="3">

Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml

@@ -138,6 +138,22 @@
 		field of the oldest event.</para>
 	    </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>

include/linux/videodev2.h

@@ -2006,6 +2006,7 @@ struct v4l2_streamparm {
 #define V4L2_EVENT_VSYNC			1
 #define V4L2_EVENT_EOS				2
 #define V4L2_EVENT_CTRL				3
+#define V4L2_EVENT_FRAME_SYNC			4
 #define V4L2_EVENT_PRIVATE_START		0x08000000
 
 /* Payload for V4L2_EVENT_VSYNC */
@@ -2032,12 +2033,17 @@ struct v4l2_event_ctrl {
 	__s32 default_value;
 };
 
+struct v4l2_event_frame_sync {
+	__u32 frame_sequence;
+};
+
 struct v4l2_event {
 	__u32				type;
 	union {
-		struct v4l2_event_vsync vsync;
-		struct v4l2_event_ctrl	ctrl;
-		__u8			data[64];
+		struct v4l2_event_vsync		vsync;
+		struct v4l2_event_ctrl		ctrl;
+		struct v4l2_event_frame_sync	frame_sync;
+		__u8				data[64];
 	} u;
 	__u32				pending;
 	__u32				sequence;