On Wednesday 14 July 2010 15:30:12 Laurent Pinchart wrote:
> As video hardware pipelines become increasingly complex and
> configurable, the current hardware description through v4l2 subdevices
> reaches its limits. In addition to enumerating and configuring
> subdevices, video camera drivers need a way to discover and modify at
> runtime how those subdevices are connected. This is done through new
> elements called entities, pads and links.
>
> 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.
>
> Links are stored in the source entity. To make backwards graph walk
> faster, a copy of all links is also stored in the sink entity. The copy
> is known as a backlink and is only used to help graph traversal.
>
> The entity API is made of three functions:
>
> - media_entity_init() initializes an entity. The caller must provide an
> array of pads as well as an estimated number of links. The links array
> is allocated dynamically and will be reallocated if it grows beyond the
> initial estimate.
>
> - media_entity_cleanup() frees resources allocated for an entity. It
> must be called during the cleanup phase after unregistering the entity
> and before freeing it.
>
> - media_entity_create_link() creates a link between two entities. An
> entry in the link array of each entity is allocated and stores pointers
> to source and sink pads.
>
> When a media device is unregistered, all its entities are unregistered
> automatically.
>
> The code is based on Hans Verkuil <[email protected]> initial work.
>
> Signed-off-by: Laurent Pinchart <[email protected]>
> Signed-off-by: Sakari Ailus <[email protected]>
> ---
> Documentation/media-framework.txt | 125 ++++++++++++++++++++++++++++++++
> drivers/media/Makefile | 2 +-
> drivers/media/media-device.c | 53 ++++++++++++++
> drivers/media/media-entity.c | 145
> +++++++++++++++++++++++++++++++++++++
> include/media/media-device.h | 16 ++++
> include/media/media-entity.h | 79 ++++++++++++++++++++
> 6 files changed, 419 insertions(+), 1 deletions(-)
> create mode 100644 drivers/media/media-entity.c
> create mode 100644 include/media/media-entity.h
>
> diff --git a/Documentation/media-framework.txt
> b/Documentation/media-framework.txt
> index b942c8f..4a8f379 100644
> --- a/Documentation/media-framework.txt
> +++ b/Documentation/media-framework.txt
> @@ -35,6 +35,30 @@ belong to userspace.
> The media kernel API aims at solving those problems.
>
>
> +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
> ------------
>
> @@ -66,3 +90,104 @@ Drivers unregister media device instances by calling
>
> 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, u8 num_pads,
> + struct media_entity_pad *pads, u8 extra_links);
> +
> +The media_entity name, type and subtype fields can be initialized before or
> +after calling media_entity_init. Entities embedded in higher-level standard
> +structures have 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 type 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);
> +
> +When registered the entity is assigned an ID. Entity IDs are positive
> integers
> +and are guaranteed to be unique in the context of the media device. The
> +framework doesn't guarantees that IDs will always be continuous.
guarantees -> guarantee
> +
> +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.
> +
> +- Pads
> +
> +Pads are represented by a struct media_entity_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_entity_pad structure, making the
> +media_entity_pad pointer the canonical way to store and pass link references.
> +
> +Pads have a type, relative to the entity they belong to:
> +
> + pads of type MEDIA_PAD_TYPE_INPUT sink data, while
> + pads of type MEDIA_PAD_TYPE_OUTPUT source data.
> +
> +- Links
> +
> +Links are represented by a struct media_entity_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, u8 source_pad,
> + struct media_entity *sink, u8 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_LINK_FLAG_ACTIVE indicates that the link is active and can be
> + used to transfer media data. When two or more links target a sink pad,
> + only one of them can be active at a time.
> + MEDIA_LINK_FLAG_IMMUTABLE indicates that the link active state can't
> + be modified at runtime. An immutable link is always active.
I would rephrase the last sentence to:
If MEDIA_LINK_FLAG_IMMUTABLE is set, then MEDIA_LINK_FLAG_ACTIVE must also be
set since an immutable link is always active.
> +
> diff --git a/drivers/media/Makefile b/drivers/media/Makefile
> index f8d8dcb..a425581 100644
> --- a/drivers/media/Makefile
> +++ b/drivers/media/Makefile
> @@ -2,7 +2,7 @@
> # 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
>
> obj-$(CONFIG_MEDIA_SUPPORT) += media.o
>
> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> index a4d3db5..6361367 100644
> --- a/drivers/media/media-device.c
> +++ b/drivers/media/media-device.c
> @@ -23,6 +23,7 @@
>
> #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,
> @@ -47,6 +48,10 @@ static void media_device_release(struct media_devnode
> *mdev)
> */
> int __must_check media_device_register(struct media_device *mdev)
> {
> + mdev->entity_id = 1;
> + INIT_LIST_HEAD(&mdev->entities);
> + spin_lock_init(&mdev->lock);
> +
> /* If dev == NULL, then name must be filled in by the caller */
> if (mdev->dev == NULL && WARN_ON(!mdev->name[0]))
> return 0;
> @@ -72,6 +77,54 @@ EXPORT_SYMBOL_GPL(media_device_register);
> */
> 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);
> +
> 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);
> + entity->id = 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);
> diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
> new file mode 100644
> index 0000000..d5a4b4c
> --- /dev/null
> +++ b/drivers/media/media-entity.c
> @@ -0,0 +1,145 @@
> +/*
> + * Media Entity support
> + *
> + * Copyright (C) 2009 Laurent Pinchart <[email protected]>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * 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 input and output 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, u8 num_pads,
> + struct media_entity_pad *pads, u8 extra_links)
> +{
> + struct media_entity_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->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(media_entity_init);
> +
> +void
> +media_entity_cleanup(struct media_entity *entity)
> +{
> + kfree(entity->links);
> +}
> +EXPORT_SYMBOL(media_entity_cleanup);
> +
> +static struct
> +media_entity_link *media_entity_add_link(struct media_entity *entity)
> +{
> + if (entity->num_links >= entity->max_links) {
> + struct media_entity_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].other->other = &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, u8 source_pad,
> + struct media_entity *sink, u8 sink_pad, u32 flags)
> +{
> + struct media_entity_link *link;
> + struct media_entity_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->other = backlink;
> + backlink->other = link;
> +
> + sink->num_backlinks++;
> +
> + return 0;
> +}
> +EXPORT_SYMBOL(media_entity_create_link);
> diff --git a/include/media/media-device.h b/include/media/media-device.h
> index 6c1fc4a..9105dc3 100644
> --- a/include/media/media-device.h
> +++ b/include/media/media-device.h
> @@ -23,8 +23,10 @@
>
> #include <linux/device.h>
> #include <linux/list.h>
> +#include <linux/spinlock.h>
>
> #include <media/media-devnode.h>
> +#include <media/media-entity.h>
>
> /* Each instance of a media device should create the media_device struct,
> * either stand-alone or embedded in a larger struct.
> @@ -43,6 +45,12 @@ struct media_device {
> struct device *dev;
> struct media_devnode devnode;
>
> + u32 entity_id;
> + struct list_head entities;
> +
> + /* Protects the entities list */
> + spinlock_t lock;
> +
> /* unique device name, by default the driver name + bus ID */
> char name[MEDIA_DEVICE_NAME_SIZE];
> };
> @@ -50,4 +58,12 @@ struct media_device {
> int __must_check media_device_register(struct media_device *mdev);
> void media_device_unregister(struct media_device *mdev);
>
> +int __must_check media_device_register_entity(struct media_device *mdev,
> + struct media_entity *entity);
> +void media_device_unregister_entity(struct media_entity *entity);
> +
> +/* Iterate over all entities. */
> +#define media_device_for_each_entity(entity, mdev) \
> + list_for_each_entry(entity, &(mdev)->entities, list)
> +
> #endif
> diff --git a/include/media/media-entity.h b/include/media/media-entity.h
> new file mode 100644
> index 0000000..0929a90
> --- /dev/null
> +++ b/include/media/media-entity.h
> @@ -0,0 +1,79 @@
> +#ifndef _MEDIA_ENTITY_H
> +#define _MEDIA_ENTITY_H
> +
> +#include <linux/list.h>
> +
> +#define MEDIA_ENTITY_TYPE_NODE 1
> +#define MEDIA_ENTITY_TYPE_SUBDEV 2
> +
> +#define MEDIA_NODE_TYPE_V4L 1
> +#define MEDIA_NODE_TYPE_FB 2
> +#define MEDIA_NODE_TYPE_ALSA 3
> +#define MEDIA_NODE_TYPE_DVB 4
> +
> +#define MEDIA_SUBDEV_TYPE_VID_DECODER 1
> +#define MEDIA_SUBDEV_TYPE_VID_ENCODER 2
> +#define MEDIA_SUBDEV_TYPE_MISC 3
Are these the subtypes? If so, I would rename this to
MEDIA_ENTITY_SUBTYPE_VID_DECODER, etc.
> +
> +#define MEDIA_LINK_FLAG_ACTIVE (1 << 0)
> +#define MEDIA_LINK_FLAG_IMMUTABLE (1 << 1)
> +
> +#define MEDIA_PAD_TYPE_INPUT 1
> +#define MEDIA_PAD_TYPE_OUTPUT 2
> +
> +struct media_entity_link {
> + struct media_entity_pad *source;/* Source pad */
> + struct media_entity_pad *sink; /* Sink pad */
> + struct media_entity_link *other;/* Link in the reverse direction */
> + u32 flags; /* Link flags (MEDIA_LINK_FLAG_*) */
> +};
> +
> +struct media_entity_pad {
> + struct media_entity *entity; /* Entity this pad belongs to */
> + u32 type; /* Pad type (MEDIA_PAD_TYPE_*) */
> + u32 index; /* Pad index in the entity pads array */
u32 seems unnecessarily wasteful. u8 should be sufficient.
I don't really like the name 'type'. Why not 'dir' for direction?
Another reason for not using the name 'type' for this is that I think we
need an actual 'type' field that describes the type of data being streamed
to/from the pad. While for now we mainly have video pads, we may also get
audio pads and perhaps vbi pads as well.
> +};
> +
> +struct media_entity {
> + struct list_head list;
> + struct media_device *parent; /* Media device this entity belongs to*/
> + u32 id; /* Entity ID, unique in the parent media
> + * device context */
> + const char *name; /* Entity name */
> + u32 type; /* Entity type (MEDIA_ENTITY_TYPE_*) */
> + u32 subtype; /* Entity subtype (type-specific) */
> +
> + u8 num_pads; /* Number of input and output pads */
> + u8 num_links; /* Number of existing links, both active
> + * and inactive */
> + u8 num_backlinks; /* Number of backlinks */
> + u8 max_links; /* Maximum number of links */
> +
> + struct media_entity_pad *pads; /* Array of pads (num_pads elements) */
> + struct media_entity_link *links;/* Array of links (max_links elements)*/
> +
> + union {
> + /* Node specifications */
> + struct {
> + u32 major;
> + u32 minor;
> + } v4l;
> + struct {
> + u32 major;
> + u32 minor;
> + } fb;
> + int alsa;
> + int dvb;
> +
> + /* Sub-device specifications */
> + /* Nothing needed yet */
> + };
> +};
> +
> +int media_entity_init(struct media_entity *entity, u8 num_pads,
> + struct media_entity_pad *pads, u8 extra_links);
> +void media_entity_cleanup(struct media_entity *entity);
> +int media_entity_create_link(struct media_entity *source, u8 source_pad,
> + struct media_entity *sink, u8 sink_pad, u32 flags);
> +
> +#endif
>
Regards,
Hans
--
Hans Verkuil - video4linux developer - sponsored by TANDBERG, part of Cisco
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