Re: [PATCH v8 05/12] media: Entity use count

[Hans Verkuil]

On Thursday, January 27, 2011 13:30:30 Laurent Pinchart wrote:
> Due to the wide differences between drivers regarding power management
> needs, the media controller does not implement power management.
> However, the media_entity structure includes a use_count field that
> media drivers can use to track the number of users of every entity for
> power management needs.
> 
> The use_count field is owned by media drivers and must not be touched by
> entity drivers. Access to the field must be protected by the media
> device graph_mutex lock.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> ---
>  Documentation/media-framework.txt |   13 ++++++++++
>  drivers/media/media-device.c      |    1 +
>  drivers/media/media-entity.c      |   46 +++++++++++++++++++++++++++++++++++++
>  include/media/media-device.h      |    4 +++
>  include/media/media-entity.h      |    5 ++++
>  5 files changed, 69 insertions(+), 0 deletions(-)
> 
> diff --git a/Documentation/media-framework.txt b/Documentation/media-framework.txt
> index 88fe379..9017a41 100644
> --- a/Documentation/media-framework.txt
> +++ b/Documentation/media-framework.txt
> @@ -258,3 +258,16 @@ When the graph traversal is complete the function will return NULL.
>  
>  Graph traversal can be interrupted at any moment. No cleanup function call is
>  required and the graph structure can be freed normally.
> +
> +
> +Use count and power handling
> +----------------------------
> +
> +Due to the wide differences between drivers regarding power management needs,
> +the media controller does not implement power management. However, the
> +media_entity structure includes a use_count field that media drivers can use to
> +track the number of users of every entity for power management needs.
> +
> +The use_count field is owned by media drivers and must not be touched by entity
> +drivers. Access to the field must be protected by the media device graph_mutex
> +lock.
> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> index b8a3ace..e4c2157 100644
> --- a/drivers/media/media-device.c
> +++ b/drivers/media/media-device.c
> @@ -73,6 +73,7 @@ int __must_check media_device_register(struct media_device *mdev)
>  	mdev->entity_id = 1;
>  	INIT_LIST_HEAD(&mdev->entities);
>  	spin_lock_init(&mdev->lock);
> +	mutex_init(&mdev->graph_mutex);
>  
>  	/* Register the device node. */
>  	mdev->devnode.fops = &media_device_fops;
> diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
> index a805f20..fe6bfd2 100644
> --- a/drivers/media/media-entity.c
> +++ b/drivers/media/media-entity.c
> @@ -23,6 +23,7 @@
>  #include <linux/module.h>
>  #include <linux/slab.h>
>  #include <media/media-entity.h>
> +#include <media/media-device.h>
>  
>  /**
>   * media_entity_init - Initialize a media entity
> @@ -196,6 +197,51 @@ media_entity_graph_walk_next(struct media_entity_graph *graph)
>  EXPORT_SYMBOL_GPL(media_entity_graph_walk_next);
>  
>  /* -----------------------------------------------------------------------------
> + * Module use count
> + */
> +
> +/*
> + * media_entity_get - Get a reference to the parent module
> + * @entity: The entity
> + *
> + * Get a reference to the parent media device module.
> + *
> + * The function will return immediately if @entity is NULL.
> + *
> + * Return a pointer to the entity on success or NULL on failure.
> + */
> +struct media_entity *media_entity_get(struct media_entity *entity)
> +{
> +	if (entity == NULL)
> +		return NULL;
> +
> +	if (entity->parent->dev &&
> +	    !try_module_get(entity->parent->dev->driver->owner))
> +		return NULL;
> +
> +	return entity;
> +}
> +EXPORT_SYMBOL_GPL(media_entity_get);
> +
> +/*
> + * media_entity_put - Release the reference to the parent module
> + * @entity: The entity
> + *
> + * Release the reference count acquired by media_entity_get().
> + *
> + * The function will return immediately if @entity is NULL.
> + */
> +void media_entity_put(struct media_entity *entity)
> +{
> +	if (entity == NULL)
> +		return;
> +
> +	if (entity->parent->dev)
> +		module_put(entity->parent->dev->driver->owner);
> +}
> +EXPORT_SYMBOL_GPL(media_entity_put);
> +
> +/* -----------------------------------------------------------------------------
>   * Links management
>   */
>  
> diff --git a/include/media/media-device.h b/include/media/media-device.h
> index 0b1ecf5..260d59c 100644
> --- a/include/media/media-device.h
> +++ b/include/media/media-device.h
> @@ -25,6 +25,7 @@
>  
>  #include <linux/device.h>
>  #include <linux/list.h>
> +#include <linux/mutex.h>
>  #include <linux/spinlock.h>
>  
>  #include <media/media-devnode.h>
> @@ -42,6 +43,7 @@
>   * @entity_id:	ID of the next entity to be registered
>   * @entities:	List of registered entities
>   * @lock:	Entities list lock
> + * @graph_mutex: Entities graph operation lock
>   *
>   * This structure represents an abstract high-level media device. It allows easy
>   * access to entities and provides basic media device-level support. The
> @@ -69,6 +71,8 @@ struct media_device {
>  
>  	/* Protects the entities list */
>  	spinlock_t lock;
> +	/* Serializes graph operations. */
> +	struct mutex graph_mutex;
>  };
>  
>  /* media_devnode to media_device */
> diff --git a/include/media/media-entity.h b/include/media/media-entity.h
> index b82f824..114541a 100644
> --- a/include/media/media-entity.h
> +++ b/include/media/media-entity.h
> @@ -81,6 +81,8 @@ struct media_entity {
>  	struct media_pad *pads;		/* Pads array (num_pads elements) */
>  	struct media_link *links;	/* Links array (max_links elements)*/
>  
> +	int use_count;			/* Use count for the entity. */

Isn't unsigned better?

> +
>  	union {
>  		/* Node specifications */
>  		struct {
> @@ -129,6 +131,9 @@ void media_entity_cleanup(struct media_entity *entity);
>  int media_entity_create_link(struct media_entity *source, u16 source_pad,
>  		struct media_entity *sink, u16 sink_pad, u32 flags);
>  
> +struct media_entity *media_entity_get(struct media_entity *entity);
> +void media_entity_put(struct media_entity *entity);
> +
>  void media_entity_graph_walk_start(struct media_entity_graph *graph,
>  		struct media_entity *entity);
>  struct media_entity *
> 

Regards,

	Hans

-- 
Hans Verkuil - video4linux developer - sponsored by Cisco
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