media: uvcvideo: Add more logging to uvc_query_ctrl()

If we fail to query the control error code there is no information on
dmesg or in uvc_dbg. This makes difficult to debug the issue.

Print a proper error message when we cannot retrieve the error code from
the device.

Reviewed-by: Hans de Goede <[email protected]>
Signed-off-by: Ricardo Ribalda <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Hans de Goede <[email protected]>
Reviewed-by: Laurent Pinchart <[email protected]>
Signed-off-by: Laurent Pinchart <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>

Author: ribalda

drivers/media/usb/uvc/uvc_video.c

@@ -117,8 +117,12 @@ int uvc_query_ctrl(struct uvc_device *dev, u8 query, u8 unit,
 	error = *(u8 *)data;
 	*(u8 *)data = tmp;
 
-	if (ret != 1)
+	if (ret != 1) {
+		dev_err_ratelimited(&dev->udev->dev,
+				    "Failed to query (%s) UVC error code control %u on unit %u: %d (exp. 1).\n",
+				    uvc_query_name(query), cs, unit, ret);
 		return ret < 0 ? ret : -EPIPE;
+	}
 
 	uvc_dbg(dev, CONTROL, "Control error %u\n", error);