V4L/DVB (13827): uvcvideo: Switch to a monotonic clock for V4L2 buffers timestamps

The realtime clock provided by do_gettimeofday() is affected by time
jumps caused by NTP or DST. Furthermore, preliminary investigation
showed that SMP systems the realtime clock is based on the CPU TSC,
and those could get slightly out of sync, resulting in jitter in the
timestamps depending on which processor handles the USB interrupts.

Instead of the realtime clock, use a monotonic high resolution clock to
timestamp the buffer. As this could in theory introduce a regression
with some userspace applications expecting a realtime clock timestamp,
add a module parameter to switch back to the realtime clock.

Thanks to Paulo Assis for pointing out and investigating the issue.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/media/video/uvc/uvcvideo.h b/drivers/media/video/uvc/uvcvideo.h
index 2337585001ea..adcba31008be 100644
--- a/drivers/media/video/uvc/uvcvideo.h
+++ b/drivers/media/video/uvc/uvcvideo.h
@@ -533,6 +533,7 @@ struct uvc_driver {
 #define UVC_WARN_MINMAX		0
 #define UVC_WARN_PROBE_DEF	1
 
+extern unsigned int uvc_clock_param;
 extern unsigned int uvc_no_drop_param;
 extern unsigned int uvc_trace_param;
 extern unsigned int uvc_timeout_param;