[PATCH v9 2/6] media: uvcvideo: Ignore empty TS packets

[Ricardo Ribalda <ribalda@chromium.org>]

Some SunplusIT cameras took a borderline interpretation of the UVC 1.5
standard, and fill the PTS and SCR fields with invalid data if the
package does not contain data.

"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

This borderline/buggy interpretation has been implemented in a variety
of devices, from directly SunplusIT and from other OEMs that rebrand
SunplusIT products. So quirking based on VID:PID will be problematic.

All the affected modules have the following extension unit:
VideoControl Interface Descriptor:
  guidExtensionCode         {82066163-7050-ab49-b8cc-b3855e8d221d}

But the vendor plans to use that GUID in the future and fix the bug,
this means that we should use heuristic to figure out the broken
packets.

This patch takes care of this.

lsusb of one of the affected cameras:

Bus 001 Device 003: ID 1bcf:2a01 Sunplus Innovation Technology Inc.
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.01
  bDeviceClass          239 Miscellaneous Device
  bDeviceSubClass         2 ?
  bDeviceProtocol         1 Interface Association
  bMaxPacketSize0        64
  idVendor           0x1bcf Sunplus Innovation Technology Inc.
  idProduct          0x2a01
  bcdDevice            0.02
  iManufacturer           1 SunplusIT Inc
  iProduct                2 HanChen Wise Camera
  iSerial                 3 01.00.00
  bNumConfigurations      1

Tested-by: HungNien Chen <hn.chen@sunplusit.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 drivers/media/usb/uvc/uvc_video.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 4ff4ab4471fe..1f416c494acc 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 +527,23 @@ 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".
+	 * Most of the vendors, clear the `UVC_STREAM_SCR` bit when the data is
+	 * not valid, other vendors always set the `UVC_STREAM_SCR` bit and
+	 * expect that the driver only samples the stc if there is data on the
+	 * packet.
+	 * Ignore all the hardware timestamp information if there is no data
+	 * and stc and sof are zero.
+	 */
+	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 +582,7 @@ 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;

-- 
2.40.0.rc1.284.g88254d51c5-goog-b4-0.11.0-dev-696ae