[media] media: Entities, pads and links

    implementing policies that belong to userspace.</para>

    <para>The media controller API aims at solving those problems.</para>

  </section>

  <section id="media-controller-model">

    <title>Media device model</title>

    <para>Discovering a device internal topology, and configuring it at runtime,

    is one of the goals of the media controller API. To achieve this, hardware

    devices are modelled as an oriented graph of building blocks called entities

    connected through pads.</para>

    <para>An entity is a basic media hardware or software building block. It can

    correspond to a large variety of logical blocks such as physical hardware

    devices (CMOS sensor for instance), logical hardware devices (a building

    block in a System-on-Chip image processing pipeline), DMA channels or

    physical connectors.</para>

    <para>A pad is a connection endpoint through which an entity can interact

    with other entities. Data (not restricted to video) produced by an entity

    flows from the entity's output to one or more entity inputs. Pads should not

    be confused with physical pins at chip boundaries.</para>

    <para>A link is a point-to-point oriented connection between two pads,

    either on the same entity or on different entities. Data flows from a source

    pad to a sink pad.</para>

  </section>

</chapter>

the kernel-side implementation of the media framework.

Abstract media device model

---------------------------

Discovering a device internal topology, and configuring it at runtime, is one

of the goals of the media framework. To achieve this, hardware devices are

modeled as an oriented graph of building blocks called entities connected

through pads.

An entity is a basic media hardware building block. It can correspond to

a large variety of logical blocks such as physical hardware devices

(CMOS sensor for instance), logical hardware devices (a building block

in a System-on-Chip image processing pipeline), DMA channels or physical

connectors.

A pad is a connection endpoint through which an entity can interact with

other entities. Data (not restricted to video) produced by an entity

flows from the entity's output to one or more entity inputs. Pads should

not be confused with physical pins at chip boundaries.

A link is a point-to-point oriented connection between two pads, either

on the same entity or on different entities. Data flows from a source

pad to a sink pad.

Media device

------------

	media_device_unregister(struct media_device *mdev);

Unregistering a media device that hasn't been registered is *NOT* safe.

Entities, pads and links

------------------------

- Entities

Entities are represented by a struct media_entity instance, defined in

include/media/media-entity.h. The structure is usually embedded into a

higher-level structure, such as a v4l2_subdev or video_device instance,

although drivers can allocate entities directly.

Drivers initialize entities by calling

	media_entity_init(struct media_entity *entity, u16 num_pads,

			  struct media_pad *pads, u16 extra_links);

The media_entity name, type, flags, revision and group_id fields can be

initialized before or after calling media_entity_init. Entities embedded in

higher-level standard structures can have some of those fields set by the

higher-level framework.

As the number of pads is known in advance, the pads array is not allocated

dynamically but is managed by the entity driver. Most drivers will embed the

pads array in a driver-specific structure, avoiding dynamic allocation.

Drivers must set the direction of every pad in the pads array before calling

media_entity_init. The function will initialize the other pads fields.

Unlike the number of pads, the total number of links isn't always known in

advance by the entity driver. As an initial estimate, media_entity_init

pre-allocates a number of links equal to the number of pads plus an optional

number of extra links. The links array will be reallocated if it grows beyond

the initial estimate.

Drivers register entities with a media device by calling

	media_device_register_entity(struct media_device *mdev,

				     struct media_entity *entity);

Entities are identified by a unique positive integer ID. Drivers can provide an

ID by filling the media_entity id field prior to registration, or request the

media controller framework to assign an ID automatically. Drivers that provide

IDs manually must ensure that all IDs are unique. IDs are not guaranteed to be

contiguous even when they are all assigned automatically by the framework.

Drivers unregister entities by calling

	media_device_unregister_entity(struct media_entity *entity);

Unregistering an entity will not change the IDs of the other entities, and the

ID will never be reused for a newly registered entity.

When a media device is unregistered, all its entities are unregistered

automatically. No manual entities unregistration is then required.

Drivers free resources associated with an entity by calling

	media_entity_cleanup(struct media_entity *entity);

This function must be called during the cleanup phase after unregistering the

entity. Note that the media_entity instance itself must be freed explicitly by

the driver if required.

Entities have flags that describe the entity capabilities and state.

	MEDIA_ENT_FL_DEFAULT indicates the default entity for a given type.

	This can be used to report the default audio and video devices or the

	default camera sensor.

Logical entity groups can be defined by setting the group ID of all member

entities to the same non-zero value. An entity group serves no purpose in the

kernel, but is reported to userspace during entities enumeration. The group_id

field belongs to the media device driver and must not by touched by entity

drivers.

Media device drivers should define groups if several entities are logically

bound together. Example usages include reporting

	- ALSA, VBI and video nodes that carry the same media stream

	- lens and flash controllers associated with a sensor

- Pads

Pads are represented by a struct media_pad instance, defined in

include/media/media-entity.h. Each entity stores its pads in a pads array

managed by the entity driver. Drivers usually embed the array in a

driver-specific structure.

Pads are identified by their entity and their 0-based index in the pads array.

Both information are stored in the media_pad structure, making the media_pad

pointer the canonical way to store and pass link references.

Pads have flags that describe the pad capabilities and state.

	MEDIA_PAD_FL_SINK indicates that the pad supports sinking data.

	MEDIA_PAD_FL_SOURCE indicates that the pad supports sourcing data.

One and only one of MEDIA_PAD_FL_SINK and MEDIA_PAD_FL_SOURCE must be set for

each pad.

- Links

Links are represented by a struct media_link instance, defined in

include/media/media-entity.h. Each entity stores all links originating at or

targetting any of its pads in a links array. A given link is thus stored

twice, once in the source entity and once in the target entity. The array is

pre-allocated and grows dynamically as needed.

Drivers create links by calling

	media_entity_create_link(struct media_entity *source, u16 source_pad,

				 struct media_entity *sink,   u16 sink_pad,

				 u32 flags);

An entry in the link array of each entity is allocated and stores pointers

to source and sink pads.

Links have flags that describe the link capabilities and state.

	MEDIA_LNK_FL_ENABLED indicates that the link is enabled and can be used

	to transfer media data. When two or more links target a sink pad, only

	one of them can be enabled at a time.

	MEDIA_LNK_FL_IMMUTABLE indicates that the link enabled state can't be

	modified at runtime. If MEDIA_LNK_FL_IMMUTABLE is set, then

	MEDIA_LNK_FL_ENABLED must also be set since an immutable link is always

	enabled.

# Makefile for the kernel multimedia device drivers.

#

media-objs	:= media-device.o media-devnode.o

media-objs	:= media-device.o media-devnode.o media-entity.o

ifeq ($(CONFIG_MEDIA_CONTROLLER),y)

  obj-$(CONFIG_MEDIA_SUPPORT) += media.o

#include <media/media-device.h>

#include <media/media-devnode.h>

#include <media/media-entity.h>

static const struct media_file_operations media_device_fops = {

	.owner = THIS_MODULE,

	if (WARN_ON(mdev->dev == NULL || mdev->model[0] == 0))

		return -EINVAL;

	mdev->entity_id = 1;

	INIT_LIST_HEAD(&mdev->entities);

	spin_lock_init(&mdev->lock);

	/* Register the device node. */

	mdev->devnode.fops = &media_device_fops;

	mdev->devnode.parent = mdev->dev;

 */

void media_device_unregister(struct media_device *mdev)

{

	struct media_entity *entity;

	struct media_entity *next;

	list_for_each_entry_safe(entity, next, &mdev->entities, list)

		media_device_unregister_entity(entity);

	device_remove_file(&mdev->devnode.dev, &dev_attr_model);

	media_devnode_unregister(&mdev->devnode);

}

EXPORT_SYMBOL_GPL(media_device_unregister);

/**

 * media_device_register_entity - Register an entity with a media device

 * @mdev:	The media device

 * @entity:	The entity

 */

int __must_check media_device_register_entity(struct media_device *mdev,

					      struct media_entity *entity)

{

	/* Warn if we apparently re-register an entity */

	WARN_ON(entity->parent != NULL);

	entity->parent = mdev;

	spin_lock(&mdev->lock);

	if (entity->id == 0)

		entity->id = mdev->entity_id++;

	else

		mdev->entity_id = max(entity->id + 1, mdev->entity_id);

	list_add_tail(&entity->list, &mdev->entities);

	spin_unlock(&mdev->lock);

	return 0;

}

EXPORT_SYMBOL_GPL(media_device_register_entity);

/**

 * media_device_unregister_entity - Unregister an entity

 * @entity:	The entity

 *

 * If the entity has never been registered this function will return

 * immediately.

 */

void media_device_unregister_entity(struct media_entity *entity)

{

	struct media_device *mdev = entity->parent;

	if (mdev == NULL)

		return;

	spin_lock(&mdev->lock);

	list_del(&entity->list);

	spin_unlock(&mdev->lock);

	entity->parent = NULL;

}

EXPORT_SYMBOL_GPL(media_device_unregister_entity);

/*

 * Media entity

 *

 * Copyright (C) 2010 Nokia Corporation

 *

 * Contacts: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

 *	     Sakari Ailus <sakari.ailus@iki.fi>

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 */

#include <linux/module.h>

#include <linux/slab.h>

#include <media/media-entity.h>

/**

 * media_entity_init - Initialize a media entity

 *

 * @num_pads: Total number of sink and source pads.

 * @extra_links: Initial estimate of the number of extra links.

 * @pads: Array of 'num_pads' pads.

 *

 * The total number of pads is an intrinsic property of entities known by the

 * entity driver, while the total number of links depends on hardware design

 * and is an extrinsic property unknown to the entity driver. However, in most

 * use cases the entity driver can guess the number of links which can safely

 * be assumed to be equal to or larger than the number of pads.

 *

 * For those reasons the links array can be preallocated based on the entity

 * driver guess and will be reallocated later if extra links need to be

 * created.

 *

 * This function allocates a links array with enough space to hold at least

 * 'num_pads' + 'extra_links' elements. The media_entity::max_links field will

 * be set to the number of allocated elements.

 *

 * The pads array is managed by the entity driver and passed to

 * media_entity_init() where its pointer will be stored in the entity structure.

 */

int

media_entity_init(struct media_entity *entity, u16 num_pads,

		  struct media_pad *pads, u16 extra_links)

{

	struct media_link *links;

	unsigned int max_links = num_pads + extra_links;

	unsigned int i;

	links = kzalloc(max_links * sizeof(links[0]), GFP_KERNEL);

	if (links == NULL)

		return -ENOMEM;

	entity->group_id = 0;

	entity->max_links = max_links;

	entity->num_links = 0;

	entity->num_backlinks = 0;

	entity->num_pads = num_pads;

	entity->pads = pads;

	entity->links = links;

	for (i = 0; i < num_pads; i++) {

		pads[i].entity = entity;

		pads[i].index = i;

	}

	return 0;

}

EXPORT_SYMBOL_GPL(media_entity_init);

void

media_entity_cleanup(struct media_entity *entity)

{

	kfree(entity->links);

}

EXPORT_SYMBOL_GPL(media_entity_cleanup);

static struct media_link *media_entity_add_link(struct media_entity *entity)

{

	if (entity->num_links >= entity->max_links) {

		struct media_link *links = entity->links;

		unsigned int max_links = entity->max_links + 2;

		unsigned int i;

		links = krealloc(links, max_links * sizeof(*links), GFP_KERNEL);

		if (links == NULL)

			return NULL;

		for (i = 0; i < entity->num_links; i++)

			links[i].reverse->reverse = &links[i];

		entity->max_links = max_links;

		entity->links = links;

	}

	return &entity->links[entity->num_links++];

}

int

media_entity_create_link(struct media_entity *source, u16 source_pad,

			 struct media_entity *sink, u16 sink_pad, u32 flags)

{

	struct media_link *link;

	struct media_link *backlink;

	BUG_ON(source == NULL || sink == NULL);

	BUG_ON(source_pad >= source->num_pads);

	BUG_ON(sink_pad >= sink->num_pads);

	link = media_entity_add_link(source);

	if (link == NULL)

		return -ENOMEM;

	link->source = &source->pads[source_pad];

	link->sink = &sink->pads[sink_pad];

	link->flags = flags;

	/* Create the backlink. Backlinks are used to help graph traversal and

	 * are not reported to userspace.

	 */

	backlink = media_entity_add_link(sink);

	if (backlink == NULL) {

		source->num_links--;

		return -ENOMEM;

	}

	backlink->source = &source->pads[source_pad];

	backlink->sink = &sink->pads[sink_pad];

	backlink->flags = flags;

	link->reverse = backlink;

	backlink->reverse = link;

	sink->num_backlinks++;

	return 0;

}

EXPORT_SYMBOL_GPL(media_entity_create_link);