Am Sonntag, den 06.06.2021, 00:56 +0300 schrieb Laurent Pinchart:
Hi Benjamin,
Thank you for the patch.
On Sat, Jun 05, 2021 at 08:15:36PM +0000, Benjamin Drung wrote:
The Elgato Cam Link 4K HDMI video capture card reports to support three different pixel formats, where the first format depends on the connected HDMI device.
$ v4l2-ctl -d /dev/video0 --list-formats-ext ioctl: VIDIOC_ENUM_FMT Type: Video Capture [0]: 'NV12' (Y/CbCr 4:2:0) Size: Discrete 3840x2160 Interval: Discrete 0.033s (29.970 fps) [1]: 'NV12' (Y/CbCr 4:2:0) Size: Discrete 3840x2160 Interval: Discrete 0.033s (29.970 fps) [2]: 'YU12' (Planar YUV 4:2:0) Size: Discrete 3840x2160 Interval: Discrete 0.033s (29.970 fps)Changing the pixel format to anything besides the first pixel format does not work:
$ v4l2-ctl -d /dev/video0 --try-fmt-video pixelformat=YU12 Format Video Capture: Width/Height : 3840/2160 Pixel Format : 'NV12' (Y/CbCr 4:2:0) Field : None Bytes per Line : 3840 Size Image : 12441600 Colorspace : sRGB Transfer Function : Rec. 709 YCbCr/HSV Encoding: Rec. 709 Quantization : Default (maps to Limited Range) Flags :User space applications like VLC might show an error message on the terminal in that case:
libv4l2: error set_fmt gave us a different result than try_fmt!Depending on the error handling of the user space applications, they might display a distorted video, because they use the wrong pixel format for decoding the stream.
The Elgato Cam Link 4K responds to the USB video probe VS_PROBE_CONTROL/VS_COMMIT_CONTROL with a malformed data structure: The second byte contains bFormatIndex (instead of being the second byte of bmHint). The first byte is always zero. The third byte is always 1.
The firmware bug was reported to Elgato on 2020-12-01 and it was forwarded by the support team to the developers as feature request. There is no firmware update available since then. The latest firmware for Elgato Cam Link 4K as of 2021-03-23 has MCU 20.02.19 and FPGA 67.
Therefore add a quirk to correct the malformed data structure.
The quirk was successfully tested with VLC, OBS, and Chromium using different pixel formats (YUYV, NV12, YU12), resolutions (3840x2160, 1920x1080), and frame rates (29.970 and 59.940 fps).
Cc: stable@vger.kernel.org Signed-off-by: Benjamin Drung bdrung@posteo.de
drivers/media/usb/uvc/uvc_video.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+)
(now sending this patch with v4 in the subject instead of falsely v3)
v2: enhanced the comment describing the quirk
v3:
- hardcode ctrl->bmHint to 1
- Use UVC_DBG_VIDEO instead of UVC_DBG_CONTROL (to match the rest of the file)
v4:
- Replace quirk bit by specific check for USB VID:PID test
I tried setting different values for bmHint, but the response from the Cam Link was always 1. So this patch hardcodes ctrl->bmHint to 1 as suggested.
Patch version 4 implements the recommendation of Laurent Pinchart. It requires defining the device ID as variable since usb_match_one_id takes an pointer to it. In case more Elgato products like Game Capture HD 60 S+ (0fd9:006a) are affected, this version is harder to extent.
Take patch version 3 or 4 depending on which version you prefer. Both work and are tested.
diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c index a777b389a66e..35c3ce0e0716 100644 --- a/drivers/media/usb/uvc/uvc_video.c +++ b/drivers/media/usb/uvc/uvc_video.c @@ -130,6 +130,31 @@ static void uvc_fixup_video_ctrl(struct uvc_streaming *stream, struct uvc_format *format = NULL; struct uvc_frame *frame = NULL; unsigned int i;
- static const struct usb_device_id elgato_cam_link_4k = { USB_DEVICE(0x0fd9, 0x0066) };
Let's avoid long line
static const struct usb_device_id elgato_cam_link_4k = { USB_DEVICE(0x0fd9, 0x0066) };
Yes. That's better readable.
- /*
* The response of the Elgato Cam Link 4K is incorrect: The second byte* contains bFormatIndex (instead of being the second byte of bmHint).* The first byte is always zero. The third byte is always 1.** The UVC 1.5 class specification defines the first five bits in the* bmHint bitfield. The remaining bits are reserved and should be zero.* Therefore a valid bmHint will be less than 32.** Latest Elgato Cam Link 4K firmware as of 2021-03-23 needs this quirk.* MCU: 20.02.19, FPGA: 67*/- if (usb_match_one_id(stream->dev->intf, &elgato_cam_link_4k) && ctrl->bmHint > 255) {
Similarly, I'd break this as
if (usb_match_one_id(stream->dev->intf, &elgato_cam_link_4k) && ctrl->bmHint > 255) {
Agreed.
__u8 corrected_format_index;You can use u8 within the kernel.
Good to know. I can't remember why I used __u8 instead.
corrected_format_index = ctrl->bmHint >> 8;uvc_dbg(stream->dev, VIDEO,"Correct USB video probe response from {bmHint: 0x%04x, bFormatIndex: 0x%02x} to {bmHint: 0x%04x, bFormatIndex: 0x%02x}.\n",I'd print bFormatIndex with %u as it's an index and thus more readable as a decimal integer.
So print bmHint as hex and bFormatIndex as integer? That would change the log from e.g.
uvcvideo: Correct USB video probe response from {bmHint: 0x0300, bFormatIndex: 0x01} to {bmHint: 0x0001, bFormatIndex: 0x03}.
to
uvcvideo: Correct USB video probe response from {bmHint: 0x0300, bFormatIndex: 1} to {bmHint: 0x0001, bFormatIndex: 3}.
That would be fine for me as well (since bFormatIndex is only one byte).
If you agree with those small changes, there's no need to resubmit, I can fold them in when applying the patch.
I agree. Thanks for reviewing it.
Reviewed-by: Laurent Pinchart laurent.pinchart@ideasonboard.com
ctrl->bmHint, ctrl->bFormatIndex,1, corrected_format_index);ctrl->bmHint = 1;ctrl->bFormatIndex = corrected_format_index;- }
for (i = 0; i < stream->nformats; ++i) { if (stream->format[i].index == ctrl->bFormatIndex) {