Hi Ricardo, On Mon, Nov 06, 2023 at 10:52:27AM +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. > --- > 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_decode_start() is called when the reception of the entire frame has been completed. However, the documentation for V4L2_EVENT_FRAME_SYNC says that the event is "Triggered immediately when the reception of a frame has begun.". The functionality here doesn't seem to fit to this patch. Wouldn't V4L2_EVENT_VSYNC be a better fit, even if we don't really have a concept of vertical sync in the case of USB? That event doesn't have the sequence though but I guess it's not an issue at least if your case. Another technically correct option could be to create a new event for this but I'm not sure it's worth it. > } > > uvc_video_clock_decode(stream, buf, data, len); > -- Regards, Sakari Ailus
