Hi Ricardo,
Thank you for the patch.
On Sat, Mar 23, 2024 at 10:48:07AM +0000, Ricardo Ribalda wrote:
> In UVC 1.5 we get a single clock value per frame. With the current
> buffer size of 32, FPS slowers than 32 might roll-over twice.
>
> The current code cannot handle two roll-over and provide invalid
> timestamps.
>
> Remove all the samples from the circular buffer that are more than two
> rollovers old, so the algorithm always provides good timestamps.
>
> Note that we are removing values that are more than one second old,
> which means that there is enough distance between the two points that
> we use for the interpolation to provide good values.
>
> Tested-by: HungNien Chen <hn.chen@xxxxxxxxxxxxx>
> Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> ---
> drivers/media/usb/uvc/uvc_video.c | 24 ++++++++++++++++++++++++
> drivers/media/usb/uvc/uvcvideo.h | 1 +
> 2 files changed, 25 insertions(+)
>
> diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> index 5df8f61d39cd1..900b57afac93a 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -471,8 +471,31 @@ static void uvc_video_clock_add_sample(struct uvc_clock *clock,
> {
> unsigned long flags;
>
> + /*
> + * If we write new data on the position where we had the last
> + * overflow, remove the overflow pointer. There is no overflow
s/overflow/SOF overflow/
otherwise it sounds like a circular buffer overflow. Same in the other
comments below.
> + * on the whole circular buffer.
> + */
> + if (clock->head == clock->last_sof_overflow)
> + clock->last_sof_overflow = -1;
> +
> spin_lock_irqsave(&clock->lock, flags);
>
> + /* Handle overflows */
s/overflows/overflows./
> + if (clock->count > 0 && clock->last_sof > sample->dev_sof) {
> + /*
> + * Remove data from the circular buffer that is older than the
> + * last overflow. We only support one overflow per circular
> + * buffer.
> + */
> + if (clock->last_sof_overflow != -1) {
> + clock->count = (clock->head - clock->last_sof_overflow
> + + clock->count) % clock->count;
If I'm following you correctly here, you want to set count to the
distance between last_sof_overflow and head. Shouldn't it be
clock->count = (clock->head - clock->last_sof_overflow
+ clock->size) % clock->size;
> + }
No need for curly braces.
> + clock->last_sof_overflow = clock->head;
> + }
> +
> + /* Add sample */
s/sample/sample./
I still think it would be nicer to handle multiple rollovers correctly,
but that probably better handled by moving all the clock handling to
userspace. With the above issues addressed, I think this patch can go
in.
I could address all these issues when applying, but I'd like the count
-> size change to be tested first. You can submit a new version of this
patch only, I've applied the rest of the series to my tree already.
> clock->samples[clock->head] = *sample;
> clock->head = (clock->head + 1) % clock->size;
> clock->count = min(clock->count + 1, clock->size);
> @@ -616,6 +639,7 @@ 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 cb9dd50bba8ac..fb9f9771131ac 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -499,6 +499,7 @@ 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
