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

Hans Verkuil
2011-02-04T10:22:43Z

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@ideasonboard.com>
> ---
> 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