On Mon, Nov 06, 2023 at 12:39:26PM +0200, Laurent Pinchart wrote:
> On Fri, Oct 20, 2023 at 06:41:45AM +0000, Ricardo Ribalda wrote:
> > 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.
>
> Not surprising, especially for large resolutions. I'm curious though,
> what do you use this event for ?
>
> > ---
> > drivers/media/usb/uvc/uvc_v4l2.c | 2 ++
> > drivers/media/usb/uvc/uvc_video.c | 8 +++++++-
> > 2 files changed, 9 insertions(+), 1 deletion(-)
> >
> > 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..1d4b4807b005 100644
> > --- a/drivers/media/usb/uvc/uvc_video.c
> > +++ b/drivers/media/usb/uvc/uvc_video.c
> > @@ -1073,9 +1073,15 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
> > * that discontinuous sequence numbers always indicate lost frames.
> > */
> > if (stream->last_fid != fid) {
> > - stream->sequence++;
> > + struct v4l2_event event = {
> > + .type = V4L2_EVENT_FRAME_SYNC,
> > + .u.frame_sync.frame_sequence = ++stream->sequence,
>
> Extra space before ++.
>
> It's easy to miss the ++ there when reading the code, would the
> following be more readable ?
>
> struct v4l2_event event = {
> .type = V4L2_EVENT_FRAME_SYNC,
> };
>
> stream->sequence++;
> if (stream->sequence)
> uvc_video_stats_update(stream);
>
> .u.frame_sync.frame_sequence = stream->sequence;
Obviously this should read
event.u.frame_sync.frame_sequence = stream->sequence;
> v4l2_event_queue(&stream->vdev, &event);
>
> > + };
> > +
> > if (stream->sequence)
> > uvc_video_stats_update(stream);
> > +
> > + v4l2_event_queue(&stream->vdev, &event);
> > }
> >
> > uvc_video_clock_decode(stream, buf, data, len);
> >
> > ---
> > base-commit: ce55c22ec8b223a90ff3e084d842f73cfba35588
> > change-id: 20231020-uvc-event-d3d1bbbdcb2f
--
Regards,
Laurent Pinchart
