[media] uvcvideo: Disable hardware timestamps by default

The hardware timestamping implementation has been reported as not
working correctly on at least the Logitech C920. Until this can be
fixed, disable it by default.
Reported-by: Peter Rabbitson <rabbit@rabbit.us>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/usb/uvc/uvc_driver.c

@@ -32,6 +32,7 @@
 #define DRIVER_DESC		"USB Video Class driver"
 
 unsigned int uvc_clock_param = CLOCK_MONOTONIC;
+unsigned int uvc_hw_timestamps_param;
 unsigned int uvc_no_drop_param;
 static unsigned int uvc_quirks_param = -1;
 unsigned int uvc_trace_param;
@@ -2078,6 +2079,8 @@ static int uvc_clock_param_set(const char *val, struct kernel_param *kp)
 module_param_call(clock, uvc_clock_param_set, uvc_clock_param_get,
 		  &uvc_clock_param, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(clock, "Video buffers timestamp clock");
+module_param_named(hwtimestamps, uvc_hw_timestamps_param, uint, S_IRUGO|S_IWUSR);
+MODULE_PARM_DESC(hwtimestamps, "Use hardware timestamps");
 module_param_named(nodrop, uvc_no_drop_param, uint, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(nodrop, "Don't drop incomplete frames");
 module_param_named(quirks, uvc_quirks_param, uint, S_IRUGO|S_IWUSR);

drivers/media/usb/uvc/uvc_video.c

@@ -623,6 +623,9 @@ void uvc_video_clock_update(struct uvc_streaming *stream,
 	u32 rem;
 	u64 y;
 
+	if (!uvc_hw_timestamps_param)
+		return;
+
 	spin_lock_irqsave(&clock->lock, flags);
 
 	if (clock->count < clock->size)

drivers/media/usb/uvc/uvcvideo.h

@@ -593,6 +593,7 @@ 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;
+extern unsigned int uvc_hw_timestamps_param;
 
 #define uvc_trace(flag, msg...) \
 	do { \