Hi Laurent On Mon, 12 Feb 2024 at 23:59, Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > 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 ? Take a look to: https://godbolt.org/z/xYeqTx6ba The expression only works because the size is a power of two. In this set I am allowing sizes that are not powers of two. Regards! > > > 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 -- Ricardo Ribalda
