From a0df8d9450dff25652b628a07f9240ea66228eba Mon Sep 17 00:00:00 2001 From: Ricardo Ribalda Date: Sat, 23 Mar 2024 10:48:02 +0000 Subject: media: uvcvideo: Support timestamp lists of any size The tail of the list lives at the position before the head. This is mathematically noted as: ``` (head-1) mod size. ``` Unfortunately C, does not have a modulus operator, but a remainder operator (%). The reminder operation has a different result than the modulus if (head -1) is a negative number and size is not a power of two. Adding size to (head-1) allows the code to run with any value of size. This does not change the current behaviour of the driver, as the size is always a power of two, but avoid tedious debugging if we ever change its size. Reviewed-by: Sergey Senozhatsky Signed-off-by: Ricardo Ribalda Reviewed-by: Tomasz Figa Reviewed-by: Laurent Pinchart Link: https://lore.kernel.org/r/20240323-resend-hwtimestamp-v10-1-b08e590d97c7@chromium.org Signed-off-by: Laurent Pinchart --- 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 7cbf4692bd87..659c9e9880a9 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); -- cgit