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

[Adam Goode]

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+.

Signed-off-by: Adam Goode <agoode@xxxxxxxxxx>
---
 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;
+	}
 	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)
-- 
2.28.0.297.g1956fa8f8d-goog