media: uvcvideo: Implement V4L2_EVENT_FRAME_SYNC

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

Suggested-by: Esker Wong <esker@chromium.org>
Tested-by: Esker Wong <esker@chromium.org>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
We have measured a latency of around 30msecs between frame sync
and dqbuf.
---
 drivers/media/usb/uvc/uvc_v4l2.c  | 2 ++
 drivers/media/usb/uvc/uvc_video.c | 8 +++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)


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

Best regards,
  

Friendly ping (in text mode :P)
  

Hi Ricardo,

Thank you for the patch.

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@chromium.org>
> Tested-by: Esker Wong <esker@chromium.org>
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
> 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;
		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
  

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@chromium.org>
> > Tested-by: Esker Wong <esker@chromium.org>
> > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> > ---
> > 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
  

Hi Laurent

On Mon, 6 Nov 2023 at 11:42, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> 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@chromium.org>
> > > Tested-by: Esker Wong <esker@chromium.org>
> > > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> > > ---
> > > 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 ?

I think Esker is using it to get more accurate power measurements of
the camera stack.

> > It's easy to miss the ++ there when reading the code, would the
> > following be more readable ?

Actually that was my original code, but I thought you would like this better :)

Thanks for the review, a v2 is on its way.

> --
> Regards,
>
> Laurent Pinchart
  

On Mon, Nov 06, 2023 at 11:51:06AM +0100, Ricardo Ribalda wrote:
> On Mon, 6 Nov 2023 at 11:42, Laurent Pinchart wrote:
> > 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@chromium.org>
> > > > Tested-by: Esker Wong <esker@chromium.org>
> > > > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> > > > ---
> > > > 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 ?
> 
> I think Esker is using it to get more accurate power measurements of
> the camera stack.

Esker, would you be able to provide more information ?

> > > It's easy to miss the ++ there when reading the code, would the
> > > following be more readable ?
> 
> Actually that was my original code, but I thought you would like this better :)
> 
> Thanks for the review, a v2 is on its way.

Thank you.