[PATCH v3] V4L: dynamically allocate video_device nodes in subdevices

[Guennadi Liakhovetski <g.liakhovetski@xxxxxx>]

Currently only very few drivers actually use video_device nodes, embedded
in struct v4l2_subdev. Allocate these nodes dynamically for those drivers
to save memory for the rest.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@xxxxxx>
---

v3: addressed comments from Laurent Pinchart - thanks

1. switch to using a device-release method, instead of freeing directly in 
v4l2_device_unregister_subdev()

2. switch to using drvdata instead of a wrapper struct

 drivers/media/video/v4l2-device.c |   41 ++++++++++++++++++++++++++++++++----
 include/media/v4l2-subdev.h       |    4 +-
 2 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/drivers/media/video/v4l2-device.c b/drivers/media/video/v4l2-device.c
index c72856c..9bf3d70 100644
--- a/drivers/media/video/v4l2-device.c
+++ b/drivers/media/video/v4l2-device.c
@@ -21,6 +21,7 @@
 #include <linux/types.h>
 #include <linux/ioctl.h>
 #include <linux/i2c.h>
+#include <linux/slab.h>
 #if defined(CONFIG_SPI)
 #include <linux/spi/spi.h>
 #endif
@@ -191,6 +192,13 @@ int v4l2_device_register_subdev(struct v4l2_device *v4l2_dev,
 }
 EXPORT_SYMBOL_GPL(v4l2_device_register_subdev);
 
+void v4l2_device_release_subdev_node(struct video_device *vdev)
+{
+	struct v4l2_subdev *sd = video_get_drvdata(vdev);
+	sd->devnode = NULL;
+	kfree(vdev);
+}
+
 int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
 {
 	struct video_device *vdev;
@@ -204,22 +212,42 @@ int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
 		if (!(sd->flags & V4L2_SUBDEV_FL_HAS_DEVNODE))
 			continue;
 
-		vdev = &sd->devnode;
+		vdev = kzalloc(sizeof(*vdev), GFP_KERNEL);
+		if (!vdev) {
+			err = -ENOMEM;
+			goto clean_up;
+		}
+
+		video_set_drvdata(vdev, sd);
 		strlcpy(vdev->name, sd->name, sizeof(vdev->name));
 		vdev->v4l2_dev = v4l2_dev;
 		vdev->fops = &v4l2_subdev_fops;
-		vdev->release = video_device_release_empty;
+		vdev->release = v4l2_device_release_subdev_node;
 		vdev->ctrl_handler = sd->ctrl_handler;
 		err = __video_register_device(vdev, VFL_TYPE_SUBDEV, -1, 1,
 					      sd->owner);
-		if (err < 0)
-			return err;
+		if (err < 0) {
+			kfree(vdev);
+			goto clean_up;
+		}
+		get_device(&vdev->dev);
 #if defined(CONFIG_MEDIA_CONTROLLER)
 		sd->entity.v4l.major = VIDEO_MAJOR;
 		sd->entity.v4l.minor = vdev->minor;
 #endif
+		sd->devnode = vdev;
 	}
 	return 0;
+
+clean_up:
+	list_for_each_entry(sd, &v4l2_dev->subdevs, list) {
+		if (!sd->devnode)
+			break;
+		video_unregister_device(sd->devnode);
+		put_device(&sd->devnode->dev);
+	}
+
+	return err;
 }
 EXPORT_SYMBOL_GPL(v4l2_device_register_subdev_nodes);
 
@@ -245,7 +273,10 @@ void v4l2_device_unregister_subdev(struct v4l2_subdev *sd)
 	if (v4l2_dev->mdev)
 		media_device_unregister_entity(&sd->entity);
 #endif
-	video_unregister_device(&sd->devnode);
+	if (sd->devnode) {
+		video_unregister_device(sd->devnode);
+		put_device(&sd->devnode->dev);
+	}
 	module_put(sd->owner);
 }
 EXPORT_SYMBOL_GPL(v4l2_device_unregister_subdev);
diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
index 257da1a..5dd049a 100644
--- a/include/media/v4l2-subdev.h
+++ b/include/media/v4l2-subdev.h
@@ -534,13 +534,13 @@ struct v4l2_subdev {
 	void *dev_priv;
 	void *host_priv;
 	/* subdev device node */
-	struct video_device devnode;
+	struct video_device *devnode;
 };
 
 #define media_entity_to_v4l2_subdev(ent) \
 	container_of(ent, struct v4l2_subdev, entity)
 #define vdev_to_v4l2_subdev(vdev) \
-	container_of(vdev, struct v4l2_subdev, devnode)
+	video_get_drvdata(vdev)
 
 /*
  * Used for storing subdev information per file handle
-- 
1.7.2.5

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