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 <hverkuil@xxxxxxxxx> initial work.
Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxxxxxxxxxxxxx>
---
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.
+
+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.
+
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 <laurent.pinchart@xxxxxxxxxxxxxxxx>
+ *
+ * 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
+
+#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 */
+};
+
+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
--
1.7.1
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