[media] usb/uvc: Support for V4L2_CTRL_WHICH_DEF_VAL

This driver does not use the control infrastructure.
Add support for the new field which on structure
 v4l2_ext_controls

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/usb/uvc/uvc_v4l2.c

@@ -983,6 +983,22 @@ static int uvc_ioctl_g_ext_ctrls(struct file *file, void *fh,
 	unsigned int i;
 	int ret;
 
+	if (ctrls->which == V4L2_CTRL_WHICH_DEF_VAL) {
+		for (i = 0; i < ctrls->count; ++ctrl, ++i) {
+			struct v4l2_queryctrl qc = { .id = ctrl->id };
+
+			ret = uvc_query_v4l2_ctrl(chain, &qc);
+			if (ret < 0) {
+				ctrls->error_idx = i;
+				return ret;
+			}
+
+			ctrl->value = qc.default_value;
+		}
+
+		return 0;
+	}
+
 	ret = uvc_ctrl_begin(chain);
 	if (ret < 0)
 		return ret;
@@ -1010,6 +1026,10 @@ static int uvc_ioctl_s_try_ext_ctrls(struct uvc_fh *handle,
 	unsigned int i;
 	int ret;
 
+	/* Default value cannot be changed */
+	if (ctrls->which == V4L2_CTRL_WHICH_DEF_VAL)
+		return -EINVAL;
+
 	ret = uvc_ctrl_begin(chain);
 	if (ret < 0)
 		return ret;