[media] media_device: add a topology version field

Every time a graph object is added or removed, the version
of the topology changes. That's a requirement for the new
MEDIA_IOC_G_TOPOLOGY, in order to allow userspace to know
that the topology has changed after a previous call to it.
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/media-entity.c

@@ -173,6 +173,9 @@ void media_gobj_init(struct media_device *mdev,
 		list_add_tail(&gobj->list, &mdev->interfaces);
 		break;
 	}
+
+	mdev->topology_version++;
+
 	dev_dbg_obj(__func__, gobj);
 }
 
@@ -187,6 +190,8 @@ void media_gobj_remove(struct media_gobj *gobj)
 {
 	dev_dbg_obj(__func__, gobj);
 
+	gobj->mdev->topology_version++;
+
 	/* Remove the object from mdev list */
 	list_del(&gobj->list);
 }

include/media/media-device.h

@@ -41,6 +41,8 @@ struct device;
  * @bus_info:	Unique and stable device location identifier
  * @hw_revision: Hardware device revision
  * @driver_version: Device driver version
+ * @topology_version: Monotonic counter for storing the version of the graph
+ *		topology. Should be incremented each time the topology changes.
  * @entity_id:	Unique ID used on the last entity registered
  * @pad_id:	Unique ID used on the last pad registered
  * @link_id:	Unique ID used on the last link registered
@@ -74,6 +76,8 @@ struct media_device {
 	u32 hw_revision;
 	u32 driver_version;
 
+	u32 topology_version;
+
 	u32 entity_id;
 	u32 pad_id;
 	u32 link_id;