Em 20-08-2010 12:29, Laurent Pinchart escreveu:
> From: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxxxxxxxxxxxxx>
>
> Basically these are the interface functions:
>
> media_entity_get() - acquire entity
> media_entity_put() - release entity
>
> If the entity is of node type, the power change is distributed to
> all connected entities. For non-nodes it only affects that very
> node. A mutex is used to serialise access to the entity graph.
>
> In the background there's a depth-first search algorithm that traverses the
> active links in the graph. All these functions parse the graph to implement
> whatever they're to do.
>
> The module counters are increased/decreased in media_entity_get/put to
> prevent module unloading when an entity is referenced.
>
> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> Signed-off-by: Stanimir Varbanov <svarbanov@xxxxxxxxxx>
> ---
> Documentation/media-framework.txt | 37 +++++++++
> drivers/media/media-device.c | 1 +
> drivers/media/media-entity.c | 146 +++++++++++++++++++++++++++++++++++++
> include/media/media-device.h | 4 +
> include/media/media-entity.h | 15 ++++
> 5 files changed, 203 insertions(+), 0 deletions(-)
>
> diff --git a/Documentation/media-framework.txt b/Documentation/media-framework.txt
> index a599824..59649e9 100644
> --- a/Documentation/media-framework.txt
> +++ b/Documentation/media-framework.txt
> @@ -278,3 +278,40 @@ 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.
>
> +
> +Reference counting and power handling
> +-------------------------------------
> +
> +Before accessing type-specific entities operations (such as the V4L2
> +sub-device operations), drivers must acquire a reference to the entity. This
> +ensures that the entity will be powered on and ready to accept requests.
> +Similarly, after being done with an entity, drivers must release the
> +reference.
> +
> + media_entity_get(struct media_entity *entity)
> +
> +The function will increase the entity reference count. If the entity is a node
> +(MEDIA_ENTITY_TYPE_NODE type), the reference count of all entities it is
> +connected to, both directly or indirectly, through active links is increased.
> +This ensures that the whole media pipeline will be ready to process
> +
> +Acquiring a reference to an entity increases the media device module reference
> +count to prevent module unloading when an entity is being used.
> +
> +media_entity_get will return a pointer to the entity if successful, or NULL
> +otherwise.
> +
> + media_entity_put(struct media_entity *entity)
> +
> +The function will decrease the entity reference count and, for node entities,
> +like media_entity_get, the reference count of all connected entities. Calling
> +media_entity_put with a NULL argument is valid and will return immediately.
> +
> +When the first reference to an entity is acquired, or the last reference
> +released, the entity's set_power operation is called. Entity drivers must
> +implement the operation if they need to perform any power management task,
> +such as turning powers or clocks on or off. If no power management is
> +required, drivers don't need to provide a set_power operation. The operation
> +is allowed to fail when turning power on, in which case the media_entity_get
> +function will return NULL.
The idea of doing power management via media entity get/put doesn't seem right.
The mediabus interface and its usage should be optional, and only specialized
applications will likely implement it. If a refcount 0 means power off, it ends
that a device implementing the media bus will not work with V4L2 applications.
> +
> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> index eeb002e..c309d3c 100644
> --- a/drivers/media/media-device.c
> +++ b/drivers/media/media-device.c
> @@ -71,6 +71,7 @@ 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 c277c18..da4fef6 100644
> --- a/drivers/media/media-entity.c
> +++ b/drivers/media/media-entity.c
> @@ -21,6 +21,7 @@
> #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
> @@ -194,6 +195,151 @@ media_entity_graph_walk_next(struct media_entity_graph *graph)
> EXPORT_SYMBOL_GPL(media_entity_graph_walk_next);
>
> /* -----------------------------------------------------------------------------
> + * Power state handling
> + */
> +
> +/* Apply use count to an entity. */
> +static void media_entity_use_apply_one(struct media_entity *entity, int change)
> +{
> + entity->use_count += change;
> + WARN_ON(entity->use_count < 0);
Instead of producing a warning, just deny it to have usage bellow zero. As this will
be called from userspace, the entire interface should be reliable enough to avoid
dumb applications to miss-use it.
Also: what happens if an userspace application dies or suffer any troubles? You
need to reset all use_count's at release() callback.
> +}
> +
> +/*
> + * Apply use count change to an entity and change power state based on
> + * new use count.
> + */
> +static int media_entity_power_apply_one(struct media_entity *entity, int change)
> +{
> + int ret;
> +
> + if (entity->use_count == 0 && change > 0 &&
> + entity->ops && entity->ops->set_power) {
> + ret = entity->ops->set_power(entity, 1);
> + if (ret)
> + return ret;
> + }
> +
> + media_entity_use_apply_one(entity, change);
> +
> + if (entity->use_count == 0 && change < 0 &&
> + entity->ops && entity->ops->set_power)
> + entity->ops->set_power(entity, 0);
> +
> + return 0;
> +}
> +
> +/*
> + * Apply power change to all connected entities. This ignores the
> + * nodes.
> + */
> +static int media_entity_power_apply(struct media_entity *entity, int change)
> +{
> + struct media_entity_graph graph;
> + struct media_entity *first = entity;
> + int ret = 0;
> +
> + if (!change)
> + return 0;
> +
> + media_entity_graph_walk_start(&graph, entity);
> +
> + while (!ret && (entity = media_entity_graph_walk_next(&graph)))
> + if (media_entity_type(entity) != MEDIA_ENTITY_TYPE_NODE)
> + ret = media_entity_power_apply_one(entity, change);
> +
> + if (!ret)
> + return 0;
> +
> + media_entity_graph_walk_start(&graph, first);
> +
> + while ((first = media_entity_graph_walk_next(&graph))
> + && first != entity)
> + if (media_entity_type(first) != MEDIA_ENTITY_TYPE_NODE)
> + media_entity_power_apply_one(first, -change);
> +
> + return ret;
> +}
> +
> +/*
> + * Apply use count change to graph and change power state of entities
> + * accordingly.
> + */
> +static int media_entity_node_power_change(struct media_entity *entity,
> + int change)
> +{
> + /* Apply use count to node. */
> + media_entity_use_apply_one(entity, change);
> +
> + /* Apply power change to connected non-nodes. */
> + return media_entity_power_apply(entity, change);
> +}
> +
> +/*
> + * Node entity use changes are reflected on power state of all
> + * connected (directly or indirectly) entities whereas non-node entity
> + * use count changes are limited to that very entity.
> + */
> +static int media_entity_use_change(struct media_entity *entity, int change)
> +{
> + if (media_entity_type(entity) == MEDIA_ENTITY_TYPE_NODE)
> + return media_entity_node_power_change(entity, change);
> + else
> + return media_entity_power_apply_one(entity, change);
> +}
> +
> +static struct media_entity *__media_entity_get(struct media_entity *entity)
> +{
> + if (media_entity_use_change(entity, 1))
> + return NULL;
> +
> + return entity;
> +}
> +
> +static void __media_entity_put(struct media_entity *entity)
> +{
> + media_entity_use_change(entity, -1);
> +}
> +
> +/* user open()s media entity */
> +struct media_entity *media_entity_get(struct media_entity *entity)
> +{
> + struct media_entity *e;
> +
> + if (entity == NULL)
> + return NULL;
> +
> + if (entity->parent->dev &&
> + !try_module_get(entity->parent->dev->driver->owner))
> + return NULL;
> +
> + mutex_lock(&entity->parent->graph_mutex);
> + e = __media_entity_get(entity);
> + mutex_unlock(&entity->parent->graph_mutex);
> +
> + if (e == NULL && entity->parent->dev)
> + module_put(entity->parent->dev->driver->owner);
> +
> + return e;
> +}
> +EXPORT_SYMBOL_GPL(media_entity_get);
> +
> +/* user release()s media entity */
> +void media_entity_put(struct media_entity *entity)
> +{
> + if (entity == NULL)
> + return;
> +
> + mutex_lock(&entity->parent->graph_mutex);
> + __media_entity_put(entity);
> + mutex_unlock(&entity->parent->graph_mutex);
> +
> + 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 7e2dac2..3c9a5e0 100644
> --- a/include/media/media-device.h
> +++ b/include/media/media-device.h
> @@ -23,6 +23,7 @@
>
> #include <linux/device.h>
> #include <linux/list.h>
> +#include <linux/mutex.h>
> #include <linux/spinlock.h>
>
> #include <media/media-devnode.h>
> @@ -40,6 +41,7 @@
> * @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
> @@ -67,6 +69,8 @@ struct media_device {
>
> /* Protects the entities list */
> spinlock_t lock;
> + /* Serializes graph operations. */
> + struct mutex graph_mutex;
> };
>
> int __must_check media_device_register(struct media_device *mdev);
> diff --git a/include/media/media-entity.h b/include/media/media-entity.h
> index 3a7c74d..edcafeb 100644
> --- a/include/media/media-entity.h
> +++ b/include/media/media-entity.h
> @@ -39,6 +39,10 @@ struct media_pad {
> unsigned long flags; /* Pad flags (MEDIA_PAD_FLAG_*) */
> };
>
> +struct media_entity_operations {
> + int (*set_power)(struct media_entity *entity, int power);
> +};
> +
> struct media_entity {
> struct list_head list;
> struct media_device *parent; /* Media device this entity belongs to*/
> @@ -59,6 +63,10 @@ struct media_entity {
> struct media_pad *pads; /* Pads array (num_pads elements) */
> struct media_link *links; /* Links array (max_links elements)*/
>
> + const struct media_entity_operations *ops; /* Entity operations */
> +
> + int use_count; /* Use count for the entity. */
> +
> union {
> /* Node specifications */
> struct {
> @@ -103,9 +111,16 @@ 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 *
> media_entity_graph_walk_next(struct media_entity_graph *graph);
>
> +#define media_entity_call(entity, operation, args...) \
> + (((entity)->ops && (entity)->ops->operation) ? \
> + (entity)->ops->operation((entity) , ##args) : -ENOIOCTLCMD)
> +
> #endif
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