media: v4l2-async: Create links during v4l2_async_match_notify()

Upon an async fwnode match, there's some typical behaviour that the
notifier and matching subdev will want to do. For example, a notifier
representing a sensor matching to an async subdev representing its
VCM will want to create an ancillary link to expose that relationship
to userspace.

To avoid lots of code in individual drivers, try to build these links
within v4l2 core.
Signed-off-by: Daniel Scally <djrscally@gmail.com>
Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/v4l2-core/v4l2-async.c

@@ -275,6 +275,24 @@ v4l2_async_nf_try_complete(struct v4l2_async_notifier *notifier)
 static int
 v4l2_async_nf_try_all_subdevs(struct v4l2_async_notifier *notifier);
 
+static int v4l2_async_create_ancillary_links(struct v4l2_async_notifier *n,
+					     struct v4l2_subdev *sd)
+{
+	struct media_link *link = NULL;
+
+#if IS_ENABLED(CONFIG_MEDIA_CONTROLLER)
+
+	if (sd->entity.function != MEDIA_ENT_F_LENS &&
+	    sd->entity.function != MEDIA_ENT_F_FLASH)
+		return 0;
+
+	link = media_create_ancillary_link(&n->sd->entity, &sd->entity);
+
+#endif
+
+	return IS_ERR(link) ? PTR_ERR(link) : 0;
+}
+
 static int v4l2_async_match_notify(struct v4l2_async_notifier *notifier,
 				   struct v4l2_device *v4l2_dev,
 				   struct v4l2_subdev *sd,
@@ -293,6 +311,19 @@ static int v4l2_async_match_notify(struct v4l2_async_notifier *notifier,
 		return ret;
 	}
 
+	/*
+	 * Depending of the function of the entities involved, we may want to
+	 * create links between them (for example between a sensor and its lens
+	 * or between a sensor's source pad and the connected device's sink
+	 * pad).
+	 */
+	ret = v4l2_async_create_ancillary_links(notifier, sd);
+	if (ret) {
+		v4l2_async_nf_call_unbind(notifier, sd, asd);
+		v4l2_device_unregister_subdev(sd);
+		return ret;
+	}
+
 	/* Remove from the waiting list */
 	list_del(&asd->list);
 	sd->asd = asd;