Hi Ricardo,
Thank you for the patch.
On Wed, Mar 15, 2023 at 02:30:17PM +0100, 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.
>
> Revome all the samples from the circular buffer that are more than two
s/Revome/Remove/
> rollovers old, so the algorithm always provides good timestamps.
Wouldn't it be better to support multiple rollovers instead ?
> 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>
> 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 1db0d1bc80e6..c58b51207be6 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
> + * 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 */
> + 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;
> + }
> + clock->last_sof_overflow = clock->head;
> + }
> +
> + /* Add sample */
> memcpy(&clock->samples[clock->head], sample, sizeof(*sample));
> clock->head = (clock->head + 1) % clock->size;
> clock->count = min(clock->count + 1, clock->size);
> @@ -605,6 +628,7 @@ 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 07b2fdb80adf..bf9f5162b833 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
