media: uvcvideo: Return the number of processed controls

If we let know our callers that we have not done anything, they will be
able to optimize their decisions.

Cc: stable@kernel.org
Fixes: b401200 ("[media] uvcvideo: Add support for control events")
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Message-ID: <20250224-uvc-data-backup-v2-1-de993ed9823b@chromium.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>

Author: ribalda

drivers/media/usb/uvc/uvc_ctrl.c

@@ -2101,12 +2101,17 @@ int uvc_ctrl_begin(struct uvc_video_chain *chain)
 	return mutex_lock_interruptible(&chain->ctrl_mutex) ? -ERESTARTSYS : 0;
 }
 
+/*
+ * Returns the number of uvc controls that have been correctly set, or a
+ * negative number if there has been an error.
+ */
 static int uvc_ctrl_commit_entity(struct uvc_device *dev,
 				  struct uvc_fh *handle,
 				  struct uvc_entity *entity,
 				  int rollback,
 				  struct uvc_control **err_ctrl)
 {
+	unsigned int processed_ctrls = 0;
 	struct uvc_control *ctrl;
 	unsigned int i;
 	int ret;
@@ -2141,6 +2146,9 @@ static int uvc_ctrl_commit_entity(struct uvc_device *dev,
 		else
 			ret = 0;
 
+		if (!ret)
+			processed_ctrls++;
+
 		if (rollback || ret < 0)
 			memcpy(uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT),
 			       uvc_ctrl_data(ctrl, UVC_CTRL_DATA_BACKUP),
@@ -2159,7 +2167,7 @@ static int uvc_ctrl_commit_entity(struct uvc_device *dev,
 		}
 	}
 
-	return 0;
+	return processed_ctrls;
 }
 
 static int uvc_ctrl_find_ctrl_idx(struct uvc_entity *entity,
@@ -2206,6 +2214,7 @@ int __uvc_ctrl_commit(struct uvc_fh *handle, int rollback,
 
 	if (!rollback)
 		uvc_ctrl_send_events(handle, ctrls->controls, ctrls->count);
+	ret = 0;
 done:
 	mutex_unlock(&chain->ctrl_mutex);
 	return ret;