Re: [PATCH v4] V4L: dynamically allocate video_device nodes in subdevices

[Sylwester Nawrocki <s.nawrocki@samsung.com>]

Hi Guennadi,

On 09/13/2011 04:48 PM, Guennadi Liakhovetski wrote:
> 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@gmx.de>

I have tested this patch with Samsung FIMC driver and with MC enabled
sensor driver.
After some hundreds of module load/unload I didn't observe anything unusual.
The patch seem to be safe for device node enabled subdevs. You can stick my:

Tested-by: Sylwester Nawrocki <s.nawrocki@samsung.com>

if you feel so.


Thanks,
Sylwester Nawrocki
Samsung Poland R&D Center

> ---
> 
> v4:
> 
> 1. added "static" in v4l2_device_release_subdev_node() definition
> 2. removed superfluous get_device() and put_device() (thanks to Laurent 
> for pointing out)
> 
>  drivers/media/video/v4l2-device.c |   36 +++++++++++++++++++++++++++++++-----
>  include/media/v4l2-subdev.h       |    4 ++--
>  2 files changed, 33 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/media/video/v4l2-device.c b/drivers/media/video/v4l2-device.c
> index c72856c..8abf830 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);
>  
> +static 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 +212,40 @@ 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;
> +		}
>  #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);
> +	}
> +
> +	return err;
>  }
>  EXPORT_SYMBOL_GPL(v4l2_device_register_subdev_nodes);
>  
> @@ -245,7 +271,7 @@ 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);
> +	video_unregister_device(sd->devnode);
>  	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


-- 
Sylwester Nawrocki
Samsung Poland R&D Center