media: Improvements to link validation in media graph

-----BEGIN PGP SIGNATURE-----
 
 iJgEABYKAEAWIQTAnvhxs4J7QT+XHKnMPy2AAyfeZAUCZsyE6yIcbGF1cmVudC5w
 aW5jaGFydEBpZGVhc29uYm9hcmQuY29tAAoJEMw/LYADJ95k7BQBAPr1eeaeSOtm
 263AFY9iCU0nSOziFfF1GdUeffxflPk/AP9pj9rQbHRds0U4pPJaz9RgfTi7OQ6I
 WXk1BFD3FJM9Cw==
 =WENl
 -----END PGP SIGNATURE-----

Merge tag 'next-media-20240826' of git://git.kernel.org/pub/scm/linux/kernel/git/pinchartl/linux.git

Improvements to link validation in media graph.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://patchwork.linuxtv.org/project/linux-media/patch/20240826141040.GC11033@pendragon.ideasonboard.com/

drivers/media/platform/microchip/microchip-isc-base.c

@@ -902,8 +902,11 @@ static int isc_set_fmt(struct isc_device *isc, struct v4l2_format *f)
 	return 0;
 }
 
-static int isc_validate(struct isc_device *isc)
+static int isc_link_validate(struct media_link *link)
 {
+	struct video_device *vdev =
+		media_entity_to_video_device(link->sink->entity);
+	struct isc_device *isc = video_get_drvdata(vdev);
 	int ret;
 	int i;
 	struct isc_format *sd_fmt = NULL;
@@ -1906,20 +1909,6 @@ int microchip_isc_pipeline_init(struct isc_device *isc)
 }
 EXPORT_SYMBOL_GPL(microchip_isc_pipeline_init);
 
-static int isc_link_validate(struct media_link *link)
-{
-	struct video_device *vdev =
-		media_entity_to_video_device(link->sink->entity);
-	struct isc_device *isc = video_get_drvdata(vdev);
-	int ret;
-
-	ret = v4l2_subdev_link_validate(link);
-	if (ret)
-		return ret;
-
-	return isc_validate(isc);
-}
-
 static const struct media_entity_operations isc_entity_operations = {
 	.link_validate = isc_link_validate,
 };

drivers/media/platform/renesas/vsp1/vsp1_video.c

@@ -1081,6 +1081,27 @@ static const struct v4l2_file_operations vsp1_video_fops = {
 	.mmap = vb2_fop_mmap,
 };
 
+/* -----------------------------------------------------------------------------
+ * Media entity operations
+ */
+
+static int vsp1_video_link_validate(struct media_link *link)
+{
+	/*
+	 * Ideally, link validation should be implemented here instead of
+	 * calling vsp1_video_verify_format() in vsp1_video_streamon()
+	 * manually. That would however break userspace that start one video
+	 * device before configures formats on other video devices in the
+	 * pipeline. This operation is just a no-op to silence the warnings
+	 * from v4l2_subdev_link_validate().
+	 */
+	return 0;
+}
+
+static const struct media_entity_operations vsp1_video_media_ops = {
+	.link_validate = vsp1_video_link_validate,
+};
+
 /* -----------------------------------------------------------------------------
  * Suspend and Resume
  */
@@ -1215,6 +1236,7 @@ struct vsp1_video *vsp1_video_create(struct vsp1_device *vsp1,
 
 	/* ... and the video node... */
 	video->video.v4l2_dev = &video->vsp1->v4l2_dev;
+	video->video.entity.ops = &vsp1_video_media_ops;
 	video->video.fops = &vsp1_video_fops;
 	snprintf(video->video.name, sizeof(video->video.name), "%s %s",
 		 rwpf->entity.subdev.name, direction);

drivers/media/platform/sunxi/sun4i-csi/sun4i_csi.c

@@ -35,7 +35,18 @@ struct sun4i_csi_traits {
 	bool has_isp;
 };
 
+static int sun4i_csi_video_link_validate(struct media_link *link)
+{
+	dev_warn_once(link->graph_obj.mdev->dev,
+		      "Driver bug: link validation not implemented\n");
+	return 0;
+}
+
 static const struct media_entity_operations sun4i_csi_video_entity_ops = {
+	.link_validate = sun4i_csi_video_link_validate,
+};
+
+static const struct media_entity_operations sun4i_csi_subdev_entity_ops = {
 	.link_validate = v4l2_subdev_link_validate,
 };
 
@@ -214,6 +225,7 @@ static int sun4i_csi_probe(struct platform_device *pdev)
 	subdev->internal_ops = &sun4i_csi_subdev_internal_ops;
 	subdev->flags = V4L2_SUBDEV_FL_HAS_DEVNODE | V4L2_SUBDEV_FL_HAS_EVENTS;
 	subdev->entity.function = MEDIA_ENT_F_VID_IF_BRIDGE;
+	subdev->entity.ops = &sun4i_csi_subdev_entity_ops;
 	subdev->owner = THIS_MODULE;
 	snprintf(subdev->name, sizeof(subdev->name), "sun4i-csi-0");
 	v4l2_set_subdevdata(subdev, csi);

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

@@ -1443,16 +1443,53 @@ int v4l2_subdev_link_validate(struct media_link *link)
 	bool states_locked;
 	int ret;
 
-	if (!is_media_entity_v4l2_subdev(link->sink->entity) ||
-	    !is_media_entity_v4l2_subdev(link->source->entity)) {
-		pr_warn_once("%s of link '%s':%u->'%s':%u is not a V4L2 sub-device, driver bug!\n",
-			     !is_media_entity_v4l2_subdev(link->sink->entity) ?
-			     "sink" : "source",
-			     link->source->entity->name, link->source->index,
-			     link->sink->entity->name, link->sink->index);
-		return 0;
+	/*
+	 * Links are validated in the context of the sink entity. Usage of this
+	 * helper on a sink that is not a subdev is a clear driver bug.
+	 */
+	if (WARN_ON_ONCE(!is_media_entity_v4l2_subdev(link->sink->entity)))
+		return -EINVAL;
+
+	/*
+	 * If the source is a video device, delegate link validation to it. This
+	 * allows usage of this helper for subdev connected to a video output
+	 * device, provided that the driver implement the video output device's
+	 * .link_validate() operation.
+	 */
+	if (is_media_entity_v4l2_video_device(link->source->entity)) {
+		struct media_entity *source = link->source->entity;
+
+		if (!source->ops || !source->ops->link_validate) {
+			/*
+			 * Many existing drivers do not implement the required
+			 * .link_validate() operation for their video devices.
+			 * Print a warning to get the drivers fixed, and return
+			 * 0 to avoid breaking userspace. This should
+			 * eventually be turned into a WARN_ON() when all
+			 * drivers will have been fixed.
+			 */
+			pr_warn_once("video device '%s' does not implement .link_validate(), driver bug!\n",
+				     source->name);
+			return 0;
+		}
+
+		/*
+		 * Avoid infinite loops in case a video device incorrectly uses
+		 * this helper function as its .link_validate() handler.
+		 */
+		if (WARN_ON(source->ops->link_validate == v4l2_subdev_link_validate))
+			return -EINVAL;
+
+		return source->ops->link_validate(link);
 	}
 
+	/*
+	 * If the source is still not a subdev, usage of this helper is a clear
+	 * driver bug.
+	 */
+	if (WARN_ON(!is_media_entity_v4l2_subdev(link->source->entity)))
+		return -EINVAL;
+
 	sink_sd = media_entity_to_v4l2_subdev(link->sink->entity);
 	source_sd = media_entity_to_v4l2_subdev(link->source->entity);
 

include/media/v4l2-subdev.h

@@ -1250,6 +1250,12 @@ int v4l2_subdev_link_validate_default(struct v4l2_subdev *sd,
  * calls v4l2_subdev_link_validate_default() to ensure that
  * width, height and the media bus pixel code are equal on both
  * source and sink of the link.
+ *
+ * The function can be used as a drop-in &media_entity_ops.link_validate
+ * implementation for v4l2_subdev instances. It supports all links between
+ * subdevs, as well as links between subdevs and video devices, provided that
+ * the video devices also implement their &media_entity_ops.link_validate
+ * operation.
  */
 int v4l2_subdev_link_validate(struct media_link *link);