Hi Laurent
On Fri, 30 Dec 2022 at 15:51, Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
>
> Hi Ricardo,
>
> Thank you for the patch.
>
> On Fri, Dec 02, 2022 at 06:02:48PM +0100, Ricardo Ribalda wrote:
> > In UVC 1.5, when working with FPS under 32, there is a chance that the
> > circular buffer contains two dev_sof overflows,
>
> An explanation of why this is the case would be good in the commit
> message. Also, by overflow, are you talking about the SOF counter
> rolling over ?
>
> > but the clock interpolator
> > is only capable of handle a single overflow.
> >
> > Remove all the samples from the circular buffer that are two overflows
> > old.
>
> I would rather support multiple roll-over in the clock interpolator.
> Dropping older sampls will lead to less predictable behaviour and harder
> to debug issues.
>
Multiple roll-over would not necessarily mean better data here. We are
deleting data that is more than 1 second away, and our resolution is
1kHz, which means that we have enough data to provide good results, we
have measured that 250msec already provides good data.
>From a logical point of view, this patch is fixing a bug, not adding a
new feature, and it has been validated. I would rather add multi
roll-over as a follow-up patch, or maybe suggest implementing it in
userspace ;).
> > Tested-by: HungNien Chen <hn.chen@xxxxxxxxxxxxx>
> > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> > ---
> > drivers/media/usb/uvc/uvc_video.c | 15 +++++++++++++++
> > drivers/media/usb/uvc/uvcvideo.h | 1 +
> > 2 files changed, 16 insertions(+)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> > index c81a8362d582..6b6bd521d6c2 100644
> > --- a/drivers/media/usb/uvc/uvc_video.c
> > +++ b/drivers/media/usb/uvc/uvc_video.c
> > @@ -471,6 +471,20 @@ static void uvc_video_clock_add_sample(struct uvc_clock *clock,
> >
> > spin_lock_irqsave(&clock->lock, flags);
> >
> > + /* Delete last overflows */
> > + if (clock->head == clock->last_sof_overflow)
> > + clock->last_sof_overflow = -1;
> > +
> > + /* Handle overflows */
> > + if (clock->count > 0 && clock->last_sof > sample->dev_sof) {
> > + /* Remove data from the last^2 overflows */
> > + if (clock->last_sof_overflow != -1)
> > + clock->count = (clock->head - clock->last_sof_overflow)
> > + % clock->count;
> > + clock->last_sof_overflow = clock->head;
> > + }
> > +
> > + /* Add sample */
> > memcpy(&clock->samples[clock->head], sample, sizeof(*sample));
> > clock->last_sof = sample->dev_sof;
> > clock->head = (clock->head + 1) % clock->size;
> > @@ -594,6 +608,7 @@ static void uvc_video_clock_reset(struct uvc_clock *clock)
> > clock->head = 0;
> > clock->count = 0;
> > clock->last_sof = -1;
> > + clock->last_sof_overflow = -1;
> > clock->sof_offset = -1;
> > }
> >
> > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > index 14daa7111953..d8c520ce5a86 100644
> > --- a/drivers/media/usb/uvc/uvcvideo.h
> > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > @@ -647,6 +647,7 @@ struct uvc_streaming {
> > unsigned int head;
> > unsigned int count;
> > unsigned int size;
> > + unsigned int last_sof_overflow;
> >
> > u16 last_sof;
> > u16 sof_offset;
>
> --
> Regards,
>
> Laurent Pinchart
--
Ricardo Ribalda
