media: uvcvideo: Allow custom control mapping

Some advanced controls might not be completely implemented by vendors.

If the controls are a enumeration, UVC does not gives a way to probe
what is implemented and what is not.

Let's create a new callback function where heuristics can be implemented
to detect what is implemented and what not and update the control
mapping accordingly.
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Ricardo Ribalda <ribalda@chromium.org>

drivers/media/usb/uvc/uvc_ctrl.c

@@ -2659,6 +2659,13 @@ static void uvc_ctrl_init_ctrl(struct uvc_video_chain *chain,
 	for (i = 0; i < ARRAY_SIZE(uvc_ctrl_mappings); ++i) {
 		const struct uvc_control_mapping *mapping = &uvc_ctrl_mappings[i];
 
+		/* Let the device provide a custom mapping. */
+		if (mapping->filter_mapping) {
+			mapping = mapping->filter_mapping(chain, ctrl);
+			if (!mapping)
+				continue;
+		}
+
 		if (uvc_entity_match_guid(ctrl->entity, mapping->entity) &&
 		    ctrl->info.selector == mapping->selector)
 			__uvc_ctrl_add_mapping(chain, ctrl, mapping);

drivers/media/usb/uvc/uvcvideo.h

@@ -87,7 +87,9 @@
 
 struct gpio_desc;
 struct sg_table;
+struct uvc_control;
 struct uvc_device;
+struct uvc_video_chain;
 
 /*
  * TODO: Put the most frequently accessed fields at the beginning of
@@ -126,6 +128,9 @@ struct uvc_control_mapping {
 	s32 master_manual;
 	u32 slave_ids[2];
 
+	const struct uvc_control_mapping *(*filter_mapping)
+				(struct uvc_video_chain *chain,
+				struct uvc_control *ctrl);
 	s32 (*get)(struct uvc_control_mapping *mapping, u8 query,
 		   const u8 *data);
 	void (*set)(struct uvc_control_mapping *mapping, s32 value,