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SubjectRe: [PATCH 1/2] media: uvcvideo: Ensure all probed info is returned to v4l2
Hi Adam,

Thank you for the patch.

On Sat, Aug 22, 2020 at 09:21:33PM -0400, Adam Goode wrote:
> bFrameIndex and bFormatIndex can be negotiated by the camera during
> probing, resulting in the camera choosing a different format than
> expected. v4l2 can already accommodate such changes, but the code was
> not updating the proper fields.
>
> Without such a change, v4l2 would potentially interpret the payload
> incorrectly, causing corrupted output. This was happening on the
> Elgato HD60 S+, which currently always renegotiates to format 1.
>
> As an aside, the Elgato firmware is buggy and should not be renegotating,
> but it is still a valid thing for the camera to do. Both macOS and Windows
> will properly probe and read uncorrupted images from this camera.
>
> With this change, both qv4l2 and chromium can now read uncorrupted video
> from the Elgato HD60 S+.

Good catch. I've seen my share of buggy cameras, just not this
particular bug I suppose :-)

> Signed-off-by: Adam Goode <agoode@google.com>
> ---
> drivers/media/usb/uvc/uvc_v4l2.c | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index 0335e69b70ab..7f14096cb44d 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -247,11 +247,37 @@ static int uvc_v4l2_try_format(struct uvc_streaming *stream,
> if (ret < 0)
> goto done;
>
> + /* After the probe, update fmt with the values returned from
> + * negotiation with the device.
> + */
> + for (i = 0; i < stream->nformats; ++i) {
> + if (probe->bFormatIndex == stream->format[i].index) {
> + format = &stream->format[i];
> + break;
> + }
> + }
> + if (i == stream->nformats) {
> + uvc_trace(UVC_TRACE_FORMAT, "Unknown bFormatIndex %u.\n",
> + probe->bFormatIndex);
> + return -EINVAL;
> + }
> + for (i = 0; i < format->nframes; ++i) {
> + if (probe->bFrameIndex == format->frame[i].bFrameIndex) {
> + frame = &format->frame[i];
> + break;
> + }
> + }
> + if (i == format->nframes) {
> + uvc_trace(UVC_TRACE_FORMAT, "Unknown bFrameIndex %u.\n",
> + probe->bFrameIndex);
> + return -EINVAL;
> + }

This looks good to me. Blank lines between the different blocks would be
good to let the code breathe a little bit :-) Apart from that,

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

There's no need to resubmit the patch for such a trivial change, unless
you object, I'll add the blank lines locally.

I may submit an additional patch on top of this to share the above code
with the identical implementation in uvc_fixup_video_ctrl().

> fmt->fmt.pix.width = frame->wWidth;
> fmt->fmt.pix.height = frame->wHeight;
> fmt->fmt.pix.field = V4L2_FIELD_NONE;
> fmt->fmt.pix.bytesperline = uvc_v4l2_get_bytesperline(format, frame);
> fmt->fmt.pix.sizeimage = probe->dwMaxVideoFrameSize;
> + fmt->fmt.pix.pixelformat = format->fcc;
> fmt->fmt.pix.colorspace = format->colorspace;
>
> if (uvc_format != NULL)

--
Regards,

Laurent Pinchart

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