Hi Ricardo,
Thank you for the patch.
On Wed, Mar 15, 2023 at 02:30:12PM +0100, Ricardo Ribalda wrote:
> If head is 0, last will be addressing the index 0 instead of clock->size
> -1. Luckily clock->head is unsiged, otherwise it would be addressing
> 0xffffffff.
I'm not following you. In the expression
(clock->head - 1) % clock->size
clock->head is an unsigned int, and 1 as a signed int, so the result of
the subtraction is promoted to an unsigned int. When clock->head is 0, the expression evaluates to
0xffffffff % clock->size
clock->size is a power of two (hardcoded to 32 at the moment), so the
expression evaluates to 31, as intended.
Am I missing something ?
> Nontheless, this is not the intented behaviour and should be fixed.
>
> Fixes: 66847ef013cc ("[media] uvcvideo: Add UVC timestamps support")
> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> ---
> drivers/media/usb/uvc/uvc_video.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> index d4b023d4de7c..4ff4ab4471fe 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -732,7 +732,7 @@ void uvc_video_clock_update(struct uvc_streaming *stream,
> goto done;
>
> first = &clock->samples[clock->head];
> - last = &clock->samples[(clock->head - 1) % clock->size];
> + last = &clock->samples[(clock->head - 1 + clock->size) % clock->size];
>
> /* First step, PTS to SOF conversion. */
> delta_stc = buf->pts - (1UL << 31);
--
Regards,
Laurent Pinchart
