[media] uvcvideo: Document the struct uvc_xu_control_query query field

Several developers have reported that the lack of macros for the struct
uvc_xu_control_query query field in uvcvideo.h was confusing and forced
them to look at the driver source code to find out what applications
were supposed to pass in that field.

Add a comment to the header to clarify the expected usage of the query
field.

Reported-by: Paulo Assis <pj.assis@gmail.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/uvcvideo.h b/include/linux/uvcvideo.h
index f46a53f060d7..3b081862b9e8 100644
--- a/include/linux/uvcvideo.h
+++ b/include/linux/uvcvideo.h
@@ -58,7 +58,8 @@ struct uvc_xu_control_mapping {
 struct uvc_xu_control_query {
         __u8 unit;
         __u8 selector;
-        __u8 query;
+        __u8 query;             /* Video Class-Specific Request Code, */
+                                /* defined in linux/usb/video.h A.8.  */
         __u16 size;
         __u8 __user *data;
 };