| Message ID | 20220920-resend-hwtimestamp-v2-6-0d7978a817cc@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | uvcvideo: Fixes for hw timestamping | expand |
Hi Ricardo, Thank you for the patch. On Fri, Dec 02, 2022 at 06:02:46PM +0100, Ricardo Ribalda wrote: > With UVC 1.5 we get as little as one clock sample per frame. Which means > that it takes 32 frames to move from the software timestamp to the > hardware timestamp method. > > This results in abrupt changes in the timestamping after 32 frames (~1 > second), resulting in noticeable artifacts when used for encoding. > > With this patch we modify the update algorithm to work with whatever > amount of values are available. This too makes me thing that we should *really* move this to userspace. It will but much easier to implement clock domain translation there, with a better precision. > Tested-by: HungNien Chen <hn.chen@sunplusit.com> > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org> > --- > drivers/media/usb/uvc/uvc_video.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c > index 75c32e232f5d..7c6448c6d706 100644 > --- a/drivers/media/usb/uvc/uvc_video.c > +++ b/drivers/media/usb/uvc/uvc_video.c > @@ -742,10 +742,10 @@ void uvc_video_clock_update(struct uvc_streaming *stream, > > spin_lock_irqsave(&clock->lock, flags); > > - if (clock->count < clock->size) > + if (clock->count < 2) > goto done; > > - first = &clock->samples[clock->head]; > + first = &clock->samples[(clock->head - clock->count) % clock->size]; > last = &clock->samples[(clock->head - 1) % clock->size]; > > /* First step, PTS to SOF conversion. */ > @@ -760,6 +760,14 @@ void uvc_video_clock_update(struct uvc_streaming *stream, > if (y2 < y1) > y2 += 2048 << 16; > > + /* > + * Have at least 1/4 of a second of timestamps before we > + * try to do any calculation. Otherwise we do not have enough > + * precission. s/precission/precision/ How did you determine 250ms was the right threshold ? > + */ > + if ((y2 - y1) < (256 << 16)) > + goto done; > + > y = (u64)(y2 - y1) * (1ULL << 31) + (u64)y1 * (u64)x2 > - (u64)y2 * (u64)x1; > y = div_u64(y, x2 - x1); >
diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c index 75c32e232f5d..7c6448c6d706 100644 --- a/drivers/media/usb/uvc/uvc_video.c +++ b/drivers/media/usb/uvc/uvc_video.c @@ -742,10 +742,10 @@ void uvc_video_clock_update(struct uvc_streaming *stream, spin_lock_irqsave(&clock->lock, flags); - if (clock->count < clock->size) + if (clock->count < 2) goto done; - first = &clock->samples[clock->head]; + first = &clock->samples[(clock->head - clock->count) % clock->size]; last = &clock->samples[(clock->head - 1) % clock->size]; /* First step, PTS to SOF conversion. */ @@ -760,6 +760,14 @@ void uvc_video_clock_update(struct uvc_streaming *stream, if (y2 < y1) y2 += 2048 << 16; + /* + * Have at least 1/4 of a second of timestamps before we + * try to do any calculation. Otherwise we do not have enough + * precission. + */ + if ((y2 - y1) < (256 << 16)) + goto done; + y = (u64)(y2 - y1) * (1ULL << 31) + (u64)y1 * (u64)x2 - (u64)y2 * (u64)x1; y = div_u64(y, x2 - x1);