[media] v4l2-core: add code to check for specific ops

This patch adds a v4l2_subdev_has_op() macro and a v4l2_device_has_op macro to
quickly check if a specific subdev or any subdev supports a particular subdev
operation.
This makes it easy for drivers to disable certain ioctls if none of the subdevs
supports the necessary functionality.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

include/media/v4l2-device.h

@@ -190,4 +190,17 @@ v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev);
 			##args);					\
 })
 
+#define v4l2_device_has_op(v4l2_dev, o, f)				\
+({									\
+	struct v4l2_subdev *__sd;					\
+	bool __result = false;						\
+	list_for_each_entry(__sd, &(v4l2_dev)->subdevs, list) {		\
+		if (v4l2_subdev_has_op(__sd, o, f)) {			\
+			__result = true;				\
+			break;						\
+		}							\
+	}								\
+	__result;							\
+})
+
 #endif

include/media/v4l2-subdev.h

@@ -687,4 +687,7 @@ void v4l2_subdev_init(struct v4l2_subdev *sd,
 	((!(sd) || !(sd)->v4l2_dev || !(sd)->v4l2_dev->notify) ? -ENODEV : \
 	 (sd)->v4l2_dev->notify((sd), (notification), (arg)))
 
+#define v4l2_subdev_has_op(sd, o, f) \
+	((sd)->ops->o && (sd)->ops->o->f)
+
 #endif