diff options
Diffstat (limited to 'drivers/media/usb/uvc/uvc_video.c')
| -rw-r--r-- | drivers/media/usb/uvc/uvc_video.c | 31 |
1 files changed, 30 insertions, 1 deletions
diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c index 659c9e9880a9..b2e70fcf4eb4 100644 --- a/drivers/media/usb/uvc/uvc_video.c +++ b/drivers/media/usb/uvc/uvc_video.c @@ -478,6 +478,7 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf, ktime_t time; u16 host_sof; u16 dev_sof; + u32 dev_stc; switch (data[1] & (UVC_STREAM_PTS | UVC_STREAM_SCR)) { case UVC_STREAM_PTS | UVC_STREAM_SCR: @@ -526,6 +527,34 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf, if (dev_sof == stream->clock.last_sof) return; + dev_stc = get_unaligned_le32(&data[header_size - 6]); + + /* + * STC (Source Time Clock) is the clock used by the camera. The UVC 1.5 + * standard states that it "must be captured when the first video data + * of a video frame is put on the USB bus". This is generally understood + * as requiring devices to clear the payload header's SCR bit before + * the first packet containing video data. + * + * Most vendors follow that interpretation, but some (namely SunplusIT + * on some devices) always set the `UVC_STREAM_SCR` bit, fill the SCR + * field with 0's,and expect that the driver only processes the SCR if + * there is data in the packet. + * + * Ignore all the hardware timestamp information if we haven't received + * any data for this frame yet, the packet contains no data, and both + * STC and SOF are zero. This heuristics should be safe on compliant + * devices. This should be safe with compliant devices, as in the very + * unlikely case where a UVC 1.1 device would send timing information + * only before the first packet containing data, and both STC and SOF + * happen to be zero for a particular frame, we would only miss one + * clock sample from many and the clock recovery algorithm wouldn't + * suffer from this condition. + */ + if (buf && buf->bytesused == 0 && len == header_size && + dev_stc == 0 && dev_sof == 0) + return; + stream->clock.last_sof = dev_sof; host_sof = usb_get_current_frame_number(stream->dev->udev); @@ -564,7 +593,7 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf, spin_lock_irqsave(&stream->clock.lock, flags); sample = &stream->clock.samples[stream->clock.head]; - sample->dev_stc = get_unaligned_le32(&data[header_size - 6]); + sample->dev_stc = dev_stc; sample->dev_sof = dev_sof; sample->host_sof = host_sof; sample->host_time = time; |