[PATCH v2] media: uvcvideo: Implement V4L2_EVENT_FRAME_SYNC

[Ricardo Ribalda]

Add support for the frame_sync event, so user-space can become aware
earlier of new frames.

Suggested-by: Esker Wong <esker@xxxxxxxxxxxx>
Tested-by: Esker Wong <esker@xxxxxxxxxxxx>
Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
---
We have measured a latency of around 30msecs between frame sync
and dqbuf.
---
Changes in v2:
- Suggested by Laurent. Split sequence++ and event init.
- Link to v1: https://lore.kernel.org/r/20231020-uvc-event-v1-1-3baa0e9f6952@xxxxxxxxxxxx
---
 drivers/media/usb/uvc/uvc_v4l2.c  | 2 ++
 drivers/media/usb/uvc/uvc_video.c | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
index f4988f03640a..9f3fb5fd2375 100644
--- a/drivers/media/usb/uvc/uvc_v4l2.c
+++ b/drivers/media/usb/uvc/uvc_v4l2.c
@@ -1352,6 +1352,8 @@ static int uvc_ioctl_subscribe_event(struct v4l2_fh *fh,
 	switch (sub->type) {
 	case V4L2_EVENT_CTRL:
 		return v4l2_event_subscribe(fh, sub, 0, &uvc_ctrl_sub_ev_ops);
+	case V4L2_EVENT_FRAME_SYNC:
+		return v4l2_event_subscribe(fh, sub, 0, NULL);
 	default:
 		return -EINVAL;
 	}
diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 28dde08ec6c5..4f3a510ca4fe 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -1073,9 +1073,16 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
 	 * that discontinuous sequence numbers always indicate lost frames.
 	 */
 	if (stream->last_fid != fid) {
+		struct v4l2_event event = {
+			.type = V4L2_EVENT_FRAME_SYNC,
+		};
+
 		stream->sequence++;
 		if (stream->sequence)
 			uvc_video_stats_update(stream);
+
+		event.u.frame_sync.frame_sequence = stream->sequence,
+		v4l2_event_queue(&stream->vdev, &event);
 	}
 
 	uvc_video_clock_decode(stream, buf, data, len);

---
base-commit: ce55c22ec8b223a90ff3e084d842f73cfba35588
change-id: 20231020-uvc-event-d3d1bbbdcb2f

Best regards,
-- 
Ricardo Ribalda <ribalda@xxxxxxxxxxxx>