Hi Ricardo, Thank you for the patch. On Tue, Aug 17, 2021 at 06:12:02PM +0200, Ricardo Ribalda wrote: > Some cameras do not set pts and src if there is no camera data in the > buffer. They do this without clearing the PTS and SCR bits of the > header. This is probably done due to a strict/borderline interpretation > of the standard: > > "STC must be captured when the first video data of a video frame is put > on the USB bus." > > Eg: > buffer: 0xa7755c00 len 000012 header:0x8c stc 00000000 sof 0000 pts 00000000 > buffer: 0xa7755c00 len 000012 header:0x8c stc 00000000 sof 0000 pts 00000000 > buffer: 0xa7755c00 len 000668 header:0x8c stc 73779dba sof 070c pts 7376d37a > > Support those cameras by only decoding the clock if there is camera data > in the buffer. Which cameras do you know to be affected ? > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx> > --- > drivers/media/usb/uvc/uvc_video.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c > index e16464606b14..6d0e474671a2 100644 > --- a/drivers/media/usb/uvc/uvc_video.c > +++ b/drivers/media/usb/uvc/uvc_video.c > @@ -490,6 +490,18 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf, > if (len < header_size) > return; > > + /* > + * Some cameras when there is no camera data in a buffer, do not > + * handle properly the pts and scr. This can be due to an borderline > + * interpretation of the standard: "STC must be captured when the > + * first video data of a video frame is put on the USB bus." > + * Due to their internal design, their firmware cannot clear the > + * UVC_STREAM_PTS and UVC_STREAM_SCR bits. Which forces us to use the > + * length of the buffer to decide if pts and scr are valid or not. > + */ > + if (len == header_size) > + return; > + Won't this prevent using timestamp data provided by cameras that behave properly ? > /* Extract the timestamps: > * > * - store the frame PTS in the buffer structure -- Regards, Laurent Pinchart
