media: uvcvideo: Support partial control reads

Some cameras, like the ELMO MX-P3, do not return all the bytes
requested from a control if it can fit in less bytes.
Eg: Returning 0xab instead of 0x00ab.
usb 3-9: Failed to query (GET_DEF) UVC control 3 on unit 2: 1 (exp. 2).

Extend the returned value from the camera and return it.

Cc: stable@vger.kernel.org
Fixes: a763b9fb58be ("media: uvcvideo: Do not return positive errors in uvc_query_ctrl()")
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Link: https://lore.kernel.org/r/20241128-uvc-readless-v5-1-cf16ed282af8@chromium.org
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index e00f38dd07d93554f1e98eab43991ded05c09d9d..d2fe01bcd209e535b9cb47f41b6ed6aed7a100d6 100644 (file)
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -79,6 +79,27 @@ int uvc_query_ctrl(struct uvc_device *dev, u8 query, u8 unit,
        if (likely(ret == size))
                return 0;
 
+       /*
+        * Some devices return shorter USB control packets than expected if the
+        * returned value can fit in less bytes. Zero all the bytes that the
+        * device has not written.
+        *
+        * This quirk is applied to all controls, regardless of their data type.
+        * Most controls are little-endian integers, in which case the missing
+        * bytes become 0 MSBs. For other data types, a different heuristic
+        * could be implemented if a device is found needing it.
+        *
+        * We exclude UVC_GET_INFO from the quirk. UVC_GET_LEN does not need
+        * to be excluded because its size is always 1.
+        */
+       if (ret > 0 && query != UVC_GET_INFO) {
+               memset(data + ret, 0, size - ret);
+               dev_warn_once(&dev->udev->dev,
+                             "UVC non compliance: %s control %u on unit %u returned %d bytes when we expected %u.\n",
+                             uvc_query_name(query), cs, unit, ret, size);
+               return 0;
+       }
+
        if (ret != -EPIPE) {
                dev_err(&dev->udev->dev,
                        "Failed to query (%s) UVC control %u on unit %u: %d (exp. %u).\n",