5. Media Controller devices

5.1. Media Controller

The media controller userspace API is documented in the Media Controller uAPI book. This document focus on the kernel-side implementation of the media framework.

5.1.1. 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 modelled 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.

5.1.2. Media device

A media device is represented by a struct media_device instance, defined in include/media/media-device.h. Allocation of the structure is handled by the media device driver, usually by embedding the media_device instance in a larger driver-specific structure.

Drivers register media device instances by calling __media_device_register() via the macro media_device_register() and unregistered by calling media_device_unregister().

5.1.3. 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 v4l2_subdev or video_device instances, although drivers can allocate entities directly.

Drivers initialize entity pads by calling media_entity_pads_init().

Drivers register entities with a media device by calling media_device_register_entity() and unregistered by calling media_device_unregister_entity().

5.1.4. Interfaces

Interfaces are represented by a struct media_interface instance, defined in include/media/media-entity.h. Currently, only one type of interface is defined: a device node. Such interfaces are represented by a struct media_intf_devnode.

Drivers initialize and create device node interfaces by calling media_devnode_create() and remove them by calling: media_devnode_remove().

5.1.5. 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 struct media_pad, making the struct 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.

Note

One and only one of MEDIA_PAD_FL_SINK or MEDIA_PAD_FL_SOURCE must be set for each pad.

5.1.7. Graph traversal

The media framework provides APIs to iterate over entities in a graph.

To iterate over all entities belonging to a media device, drivers can use the media_device_for_each_entity macro, defined in include/media/media-device.h.

struct media_entity *entity;

media_device_for_each_entity(entity, mdev) {
// entity will point to each entity in turn
...
}

Drivers might also need to iterate over all entities in a graph that can be reached only through enabled links starting at a given entity. The media framework provides a depth-first graph traversal API for that purpose.

Note

Graphs with cycles (whether directed or undirected) are NOT supported by the graph traversal API. To prevent infinite loops, the graph traversal code limits the maximum depth to MEDIA_ENTITY_ENUM_MAX_DEPTH, currently defined as 16.

Drivers initiate a graph traversal by calling media_graph_walk_start()

The graph structure, provided by the caller, is initialized to start graph traversal at the given entity.

Drivers can then retrieve the next entity by calling media_graph_walk_next()

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.

Helper functions can be used to find a link between two given pads, or a pad connected to another pad through an enabled link media_entity_find_link() and media_entity_remote_pad().

5.1.8. 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 struct media_entity includes a use_count field that media drivers can use to track the number of users of every entity for power management needs.

The media_entity.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.

5.1.10. Pipelines and media streams

When starting streaming, drivers must notify all entities in the pipeline to prevent link states from being modified during streaming by calling media_pipeline_start().

The function will mark all entities connected to the given entity through enabled links, either directly or indirectly, as streaming.

The struct media_pipeline instance pointed to by the pipe argument will be stored in every entity in the pipeline. Drivers should embed the struct media_pipeline in higher-level pipeline structures and can then access the pipeline through the struct media_entity pipe field.

Calls to media_pipeline_start() can be nested. The pipeline pointer must be identical for all nested calls to the function.

media_pipeline_start() may return an error. In that case, it will clean up any of the changes it did by itself.

When stopping the stream, drivers must notify the entities with media_pipeline_stop().

If multiple calls to media_pipeline_start() have been made the same number of media_pipeline_stop() calls are required to stop streaming. The media_entity.pipe field is reset to NULL on the last nested stop call.

Link configuration will fail with -EBUSY by default if either end of the link is a streaming entity. Links that can be modified while streaming must be marked with the MEDIA_LNK_FL_DYNAMIC flag.

If other operations need to be disallowed on streaming entities (such as changing entities configuration parameters) drivers can explicitly check the media_entity stream_count field to find out if an entity is streaming. This operation must be done with the media_device graph_mutex held.

5.1.12. Media Controller Device Allocator API

When the media device belongs to more than one driver, the shared media device is allocated with the shared struct device as the key for look ups.

The shared media device should stay in registered state until the last driver unregisters it. In addition, the media device should be released when all the references are released. Each driver gets a reference to the media device during probe, when it allocates the media device. If media device is already allocated, the allocate API bumps up the refcount and returns the existing media device. The driver puts the reference back in its disconnect routine when it calls media_device_delete().

The media device is unregistered and cleaned up from the kref put handler to ensure that the media device stays in registered state until the last driver unregisters the media device.

Driver Usage

Drivers should use the appropriate media-core routines to manage the shared media device life-time handling the two states: 1. allocate -> register -> delete 2. get reference to already registered device -> delete

call media_device_delete() routine to make sure the shared media device delete is handled correctly.

driver probe: Call media_device_usb_allocate() to allocate or get a reference Call media_device_register(), if media devnode isn’t registered

driver disconnect: Call media_device_delete() to free the media_device. Freeing is handled by the kref put handler.

5.1.13. API Definitions

struct media_entity_notify

Media Entity Notify

Definition

struct media_entity_notify {
  struct list_head list;
  void *notify_data;
  void (*notify)(struct media_entity *entity, void *notify_data);
};

Members

list

List head

notify_data

Input data to invoke the callback

notify

Callback function pointer

Description

Drivers may register a callback to take action when new entities get registered with the media device. This handler is intended for creating links between existing entities and should not create entities and register them.

struct media_device_ops

Media device operations

Definition

struct media_device_ops {
  int (*link_notify)(struct media_link *link, u32 flags, unsigned int notification);
  struct media_request *(*req_alloc)(struct media_device *mdev);
  void (*req_free)(struct media_request *req);
  int (*req_validate)(struct media_request *req);
  void (*req_queue)(struct media_request *req);
};

Members

link_notify

Link state change notification callback. This callback is called with the graph_mutex held.

req_alloc

Allocate a request. Set this if you need to allocate a struct larger then struct media_request. req_alloc and req_free must either both be set or both be NULL.

req_free

Free a request. Set this if req_alloc was set as well, leave to NULL otherwise.

req_validate

Validate a request, but do not queue yet. The req_queue_mutex lock is held when this op is called.

req_queue

Queue a validated request, cannot fail. If something goes wrong when queueing this request then it should be marked as such internally in the driver and any related buffers must eventually return to vb2 with state VB2_BUF_STATE_ERROR. The req_queue_mutex lock is held when this op is called. It is important that vb2 buffer objects are queued last after all other object types are queued: queueing a buffer kickstarts the request processing, so all other objects related to the request (and thus the buffer) must be available to the driver. And once a buffer is queued, then the driver can complete or delete objects from the request before req_queue exits.

struct media_device

Media device

Definition

struct media_device {
  struct device *dev;
  struct media_devnode *devnode;
  char model[32];
  char driver_name[32];
  char serial[40];
  char bus_info[32];
  u32 hw_revision;
  u64 topology_version;
  u32 id;
  struct ida entity_internal_idx;
  int entity_internal_idx_max;
  struct list_head entities;
  struct list_head interfaces;
  struct list_head pads;
  struct list_head links;
  struct list_head entity_notify;
  struct mutex graph_mutex;
  struct media_graph pm_count_walk;
  void *source_priv;
  int (*enable_source)(struct media_entity *entity, struct media_pipeline *pipe);
  void (*disable_source)(struct media_entity *entity);
  const struct media_device_ops *ops;
  struct mutex req_queue_mutex;
  atomic_t request_id;
};

Members

dev

Parent device

devnode

Media device node

model

Device model name

driver_name

Optional device driver name. If not set, calls to MEDIA_IOC_DEVICE_INFO will return dev->driver->name. This is needed for USB drivers for example, as otherwise they’ll all appear as if the driver name was “usb”.

serial

Device serial number (optional)

bus_info

Unique and stable device location identifier

hw_revision

Hardware device revision

topology_version

Monotonic counter for storing the version of the graph topology. Should be incremented each time the topology changes.

id

Unique ID used on the last registered graph object

entity_internal_idx

Unique internal entity ID used by the graph traversal algorithms

entity_internal_idx_max

Allocated internal entity indices

entities

List of registered entities

interfaces

List of registered interfaces

pads

List of registered pads

links

List of registered links

entity_notify

List of registered entity_notify callbacks

graph_mutex

Protects access to struct media_device data

pm_count_walk

Graph walk for power state walk. Access serialised using graph_mutex.

source_priv

Driver Private data for enable/disable source handlers

enable_source

Enable Source Handler function pointer

disable_source

Disable Source Handler function pointer

ops

Operation handler callbacks

req_queue_mutex

Serialise the MEDIA_REQUEST_IOC_QUEUE ioctl w.r.t. other operations that stop or start streaming.

request_id

Used to generate unique request IDs

Description

This structure represents an abstract high-level media device. It allows easy access to entities and provides basic media device-level support. The structure can be allocated directly or embedded in a larger structure.

The parent dev is a physical device. It must be set before registering the media device.

model is a descriptive model name exported through sysfs. It doesn’t have to be unique.

enable_source is a handler to find source entity for the sink entity and activate the link between them if source entity is free. Drivers should call this handler before accessing the source.

disable_source is a handler to find source entity for the sink entity and deactivate the link between them. Drivers should call this handler to release the source.

Use-case: find tuner entity connected to the decoder entity and check if it is available, and activate the link between them from enable_source and deactivate from disable_source.

Note

Bridge driver is expected to implement and set the handler when media_device is registered or when bridge driver finds the media_device during probe. Bridge driver sets source_priv with information necessary to run enable_source and disable_source handlers. Callers should hold graph_mutex to access and call enable_source and disable_source handlers.

int media_entity_enum_init(struct media_entity_enum *ent_enum, struct media_device *mdev)

Initialise an entity enumeration

Parameters

struct media_entity_enum *ent_enum

Entity enumeration to be initialised

struct media_device *mdev

The related media device

Return

zero on success or a negative error code.

void media_device_init(struct media_device *mdev)

Initializes a media device element

Parameters

struct media_device *mdev

pointer to struct media_device

Description

This function initializes the media device prior to its registration. The media device initialization and registration is split in two functions to avoid race conditions and make the media device available to user-space before the media graph has been completed.

So drivers need to first initialize the media device, register any entity within the media device, create pad to pad links and then finally register the media device by calling media_device_register() as a final step.

void media_device_cleanup(struct media_device *mdev)

Cleanups a media device element

Parameters

struct media_device *mdev

pointer to struct media_device

Description

This function that will destroy the graph_mutex that is initialized in media_device_init().

int __media_device_register(struct media_device *mdev, struct module *owner)

Registers a media device element

Parameters

struct media_device *mdev

pointer to struct media_device

struct module *owner

should be filled with THIS_MODULE

Description

Users, should, instead, call the media_device_register() macro.

The caller is responsible for initializing the media_device structure before registration. The following fields of media_device must be set:

  • media_entity.dev must point to the parent device (usually a pci_dev, usb_interface or platform_device instance).

  • media_entity.model must be filled with the device model name as a NUL-terminated UTF-8 string. The device/model revision must not be stored in this field.

The following fields are optional:

  • media_entity.serial is a unique serial number stored as a NUL-terminated ASCII string. The field is big enough to store a GUID in text form. If the hardware doesn’t provide a unique serial number this field must be left empty.

  • media_entity.bus_info represents the location of the device in the system as a NUL-terminated ASCII string. For PCI/PCIe devices media_entity.bus_info must be set to “PCI:” (or “PCIe:”) followed by the value of pci_name(). For USB devices,the usb_make_path() function must be used. This field is used by applications to distinguish between otherwise identical devices that don’t provide a serial number.

  • media_entity.hw_revision is the hardware device revision in a driver-specific format. When possible the revision should be formatted with the KERNEL_VERSION() macro.

Note

  1. Upon successful registration a character device named media[0-9]+ is created. The device major and minor numbers are dynamic. The model name is exported as a sysfs attribute.

  2. Unregistering a media device that hasn’t been registered is NOT safe.

Return

returns zero on success or a negative error code.

media_device_register(mdev)

Registers a media device element

Parameters

mdev

pointer to struct media_device

Description

This macro calls __media_device_register() passing THIS_MODULE as the __media_device_register() second argument (owner).

void media_device_unregister(struct media_device *mdev)

Unregisters a media device element

Parameters

struct media_device *mdev

pointer to struct media_device

Description

It is safe to call this function on an unregistered (but initialised) media device.

int media_device_register_entity(struct media_device *mdev, struct media_entity *entity)

registers a media entity inside a previously registered media device.

Parameters

struct media_device *mdev

pointer to struct media_device

struct media_entity *entity

pointer to struct media_entity to be registered

Description

Entities are identified by a unique positive integer ID. The media controller framework will such ID automatically. IDs are not guaranteed to be contiguous, and the ID number can change on newer Kernel versions. So, neither the driver nor userspace should hardcode ID numbers to refer to the entities, but, instead, use the framework to find the ID, when needed.

The media_entity name, type and flags fields should be initialized before calling media_device_register_entity(). Entities embedded in higher-level standard structures can have some of those fields set by the higher-level framework.

If the device has pads, media_entity_pads_init() should be called before this function. Otherwise, the media_entity.pad and media_entity.num_pads should be zeroed before calling this function.

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.

Note

Drivers should set the entity function before calling this function. Please notice that the values MEDIA_ENT_F_V4L2_SUBDEV_UNKNOWN and MEDIA_ENT_F_UNKNOWN should not be used by the drivers.

void media_device_unregister_entity(struct media_entity *entity)

unregisters a media entity.

Parameters

struct media_entity *entity

pointer to struct media_entity to be unregistered

Description

All links associated with the entity and all PADs are automatically unregistered from the media_device when this function is called.

Unregistering an entity will not change the IDs of the other entities and the previoully used ID will never be reused for a newly registered entities.

When a media device is unregistered, all its entities are unregistered automatically. No manual entities unregistration is then required.

Note

The media_entity instance itself must be freed explicitly by the driver if required.

int media_device_register_entity_notify(struct media_device *mdev, struct media_entity_notify *nptr)

Registers a media entity_notify callback

Parameters

struct media_device *mdev

The media device

struct media_entity_notify *nptr

The media_entity_notify

Description

Note

When a new entity is registered, all the registered media_entity_notify callbacks are invoked.

void media_device_unregister_entity_notify(struct media_device *mdev, struct media_entity_notify *nptr)

Unregister a media entity notify callback

Parameters

struct media_device *mdev

The media device

struct media_entity_notify *nptr

The media_entity_notify

void media_device_pci_init(struct media_device *mdev, struct pci_dev *pci_dev, const char *name)

create and initialize a struct media_device from a PCI device.

Parameters

struct media_device *mdev

pointer to struct media_device

struct pci_dev *pci_dev

pointer to struct pci_dev

const char *name

media device name. If NULL, the routine will use the default name for the pci device, given by pci_name() macro.

void __media_device_usb_init(struct media_device *mdev, struct usb_device *udev, const char *board_name, const char *driver_name)

create and initialize a struct media_device from a PCI device.

Parameters

struct media_device *mdev

pointer to struct media_device

struct usb_device *udev

pointer to struct usb_device

const char *board_name

media device name. If NULL, the routine will use the usb product name, if available.

const char *driver_name

name of the driver. if NULL, the routine will use the name given by udev->dev->driver->name, with is usually the wrong thing to do.

Description

Note

It is better to call media_device_usb_init() instead, as such macro fills driver_name with KBUILD_MODNAME.

media_device_usb_init(mdev, udev, name)

create and initialize a struct media_device from a PCI device.

Parameters

mdev

pointer to struct media_device

udev

pointer to struct usb_device

name

media device name. If NULL, the routine will use the usb product name, if available.

Description

This macro calls media_device_usb_init() passing the media_device_usb_init() driver_name parameter filled with KBUILD_MODNAME.

struct media_file_operations

Media device file operations

Definition

struct media_file_operations {
  struct module *owner;
  ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
  ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
  __poll_t (*poll) (struct file *, struct poll_table_struct *);
  long (*ioctl) (struct file *, unsigned int, unsigned long);
  long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
  int (*open) (struct file *);
  int (*release) (struct file *);
};

Members

owner

should be filled with THIS_MODULE

read

pointer to the function that implements read() syscall

write

pointer to the function that implements write() syscall

poll

pointer to the function that implements poll() syscall

ioctl

pointer to the function that implements ioctl() syscall

compat_ioctl

pointer to the function that will handle 32 bits userspace calls to the ioctl() syscall on a Kernel compiled with 64 bits.

open

pointer to the function that implements open() syscall

release

pointer to the function that will release the resources allocated by the open function.

struct media_devnode

Media device node

Definition

struct media_devnode {
  struct media_device *media_dev;
  const struct media_file_operations *fops;
  struct device dev;
  struct cdev cdev;
  struct device *parent;
  int minor;
  unsigned long flags;
  void (*release)(struct media_devnode *devnode);
};

Members

media_dev

pointer to struct media_device

fops

pointer to struct media_file_operations with media device ops

dev

pointer to struct device containing the media controller device

cdev

struct cdev pointer character device

parent

parent device

minor

device node minor number

flags

flags, combination of the MEDIA_FLAG_* constants

release

release callback called at the end of media_devnode_release() routine at media-device.c.

Description

This structure represents a media-related device node.

The parent is a physical device. It must be set by core or device drivers before registering the node.

int media_devnode_register(struct media_device *mdev, struct media_devnode *devnode, struct module *owner)

register a media device node

Parameters

struct media_device *mdev

struct media_device we want to register a device node

struct media_devnode *devnode

media device node structure we want to register

struct module *owner

should be filled with THIS_MODULE

Description

The registration code assigns minor numbers and registers the new device node with the kernel. An error is returned if no free minor number can be found, or if the registration of the device node fails.

Zero is returned on success.

Note that if the media_devnode_register call fails, the release() callback of the media_devnode structure is not called, so the caller is responsible for freeing any data.

void media_devnode_unregister_prepare(struct media_devnode *devnode)

clear the media device node register bit

Parameters

struct media_devnode *devnode

the device node to prepare for unregister

Description

This clears the passed device register bit. Future open calls will be met with errors. Should be called before media_devnode_unregister() to avoid races with unregister and device file open calls.

This function can safely be called if the device node has never been registered or has already been unregistered.

void media_devnode_unregister(struct media_devnode *devnode)

unregister a media device node

Parameters

struct media_devnode *devnode

the device node to unregister

Description

This unregisters the passed device. Future open calls will be met with errors.

Should be called after media_devnode_unregister_prepare()

struct media_devnode * media_devnode_data(struct file *filp)

returns a pointer to the media_devnode

Parameters

struct file *filp

pointer to struct file

int media_devnode_is_registered(struct media_devnode *devnode)

returns true if media_devnode is registered; false otherwise.

Parameters

struct media_devnode *devnode

pointer to struct media_devnode.

Note

If mdev is NULL, it also returns false.

Error

kernel-doc missing

enum media_request_state

media request state

Constants

MEDIA_REQUEST_STATE_IDLE

Idle

MEDIA_REQUEST_STATE_VALIDATING

Validating the request, no state changes allowed

MEDIA_REQUEST_STATE_QUEUED

Queued

MEDIA_REQUEST_STATE_COMPLETE

Completed, the request is done

MEDIA_REQUEST_STATE_CLEANING

Cleaning, the request is being re-inited

MEDIA_REQUEST_STATE_UPDATING

The request is being updated, i.e. request objects are being added, modified or removed

NR_OF_MEDIA_REQUEST_STATE

The number of media request states, used internally for sanity check purposes

struct media_request

Media device request

Definition

struct media_request {
  struct media_device *mdev;
  struct kref kref;
  char debug_str[TASK_COMM_LEN + 11];
  enum media_request_state state;
  unsigned int updating_count;
  unsigned int access_count;
  struct list_head objects;
  unsigned int num_incomplete_objects;
  wait_queue_head_t poll_wait;
  spinlock_t lock;
};

Members

mdev

Media device this request belongs to

kref

Reference count

debug_str

Prefix for debug messages (process name:fd)

state

The state of the request

updating_count

count the number of request updates that are in progress

access_count

count the number of request accesses that are in progress

objects

List of struct media_request_object request objects

num_incomplete_objects

The number of incomplete objects in the request

poll_wait

Wait queue for poll

lock

Serializes access to this struct

int media_request_lock_for_access(struct media_request *req)

Lock the request to access its objects

Parameters

struct media_request *req

The media request

Description

Use before accessing a completed request. A reference to the request must be held during the access. This usually takes place automatically through a file handle. Use media_request_unlock_for_access when done.

void media_request_unlock_for_access(struct media_request *req)

Unlock a request previously locked for access

Parameters

struct media_request *req

The media request

Description

Unlock a request that has previously been locked using media_request_lock_for_access.

int media_request_lock_for_update(struct media_request *req)

Lock the request for updating its objects

Parameters

struct media_request *req

The media request

Description

Use before updating a request, i.e. adding, modifying or removing a request object in it. A reference to the request must be held during the update. This usually takes place automatically through a file handle. Use media_request_unlock_for_update when done.

void media_request_unlock_for_update(struct media_request *req)

Unlock a request previously locked for update

Parameters

struct media_request *req

The media request

Description

Unlock a request that has previously been locked using media_request_lock_for_update.

void media_request_get(struct media_request *req)

Get the media request

Parameters

struct media_request *req

The media request

Description

Get the media request.

void media_request_put(struct media_request *req)

Put the media request

Parameters

struct media_request *req

The media request

Description

Put the media request. The media request will be released when the refcount reaches 0.

struct media_request * media_request_get_by_fd(struct media_device *mdev, int request_fd)

Get a media request by fd

Parameters

struct media_device *mdev

Media device this request belongs to

int request_fd

The file descriptor of the request

Description

Get the request represented by request_fd that is owned by the media device.

Return a -EBADR error pointer if requests are not supported by this driver. Return -EINVAL if the request was not found. Return the pointer to the request if found: the caller will have to call media_request_put when it finished using the request.

int media_request_alloc(struct media_device *mdev, int *alloc_fd)

Allocate the media request

Parameters

struct media_device *mdev

Media device this request belongs to

int *alloc_fd

Store the request’s file descriptor in this int

Description

Allocated the media request and put the fd in alloc_fd.

struct media_request_object_ops

Media request object operations

Definition

struct media_request_object_ops {
  int (*prepare)(struct media_request_object *object);
  void (*unprepare)(struct media_request_object *object);
  void (*queue)(struct media_request_object *object);
  void (*unbind)(struct media_request_object *object);
  void (*release)(struct media_request_object *object);
};

Members

prepare

Validate and prepare the request object, optional.

unprepare

Unprepare the request object, optional.

queue

Queue the request object, optional.

unbind

Unbind the request object, optional.

release

Release the request object, required.

struct media_request_object

An opaque object that belongs to a media request

Definition

struct media_request_object {
  const struct media_request_object_ops *ops;
  void *priv;
  struct media_request *req;
  struct list_head list;
  struct kref kref;
  bool completed;
};

Members

ops

object’s operations

priv

object’s priv pointer

req

the request this object belongs to (can be NULL)

list

List entry of the object for struct media_request

kref

Reference count of the object, acquire before releasing req->lock

completed

If true, then this object was completed.

Description

An object related to the request. This struct is always embedded in another struct that contains the actual data for this request object.

void media_request_object_get(struct media_request_object *obj)

Get a media request object

Parameters

struct media_request_object *obj

The object

Description

Get a media request object.

void media_request_object_put(struct media_request_object *obj)

Put a media request object

Parameters

struct media_request_object *obj

The object

Description

Put a media request object. Once all references are gone, the object’s memory is released.

struct media_request_object * media_request_object_find(struct media_request *req, const struct media_request_object_ops *ops, void *priv)

Find an object in a request

Parameters

struct media_request *req

The media request

const struct media_request_object_ops *ops

Find an object with this ops value

void *priv

Find an object with this priv value

Description

Both ops and priv must be non-NULL.

Returns the object pointer or NULL if not found. The caller must call media_request_object_put() once it finished using the object.

Since this function needs to walk the list of objects it takes the req->lock spin lock to make this safe.

void media_request_object_init(struct media_request_object *obj)

Initialise a media request object

Parameters

struct media_request_object *obj

The object

Description

Initialise a media request object. The object will be released using the release callback of the ops once it has no references (this function initialises references to one).

int media_request_object_bind(struct media_request *req, const struct media_request_object_ops *ops, void *priv, bool is_buffer, struct media_request_object *obj)

Bind a media request object to a request

Parameters

struct media_request *req

The media request

const struct media_request_object_ops *ops

The object ops for this object

void *priv

A driver-specific priv pointer associated with this object

bool is_buffer

Set to true if the object a buffer object.

struct media_request_object *obj

The object

Description

Bind this object to the request and set the ops and priv values of the object so it can be found later with media_request_object_find().

Every bound object must be unbound or completed by the kernel at some point in time, otherwise the request will never complete. When the request is released all completed objects will be unbound by the request core code.

Buffer objects will be added to the end of the request’s object list, non-buffer objects will be added to the front of the list. This ensures that all buffer objects are at the end of the list and that all non-buffer objects that they depend on are processed first.

void media_request_object_unbind(struct media_request_object *obj)

Unbind a media request object

Parameters

struct media_request_object *obj

The object

Description

Unbind the media request object from the request.

void media_request_object_complete(struct media_request_object *obj)

Mark the media request object as complete

Parameters

struct media_request_object *obj

The object

Description

Mark the media request object as complete. Only bound objects can be completed.

struct media_device * media_device_usb_allocate(struct usb_device *udev, const char *module_name, struct module *owner)

Allocate and return struct media device

Parameters

struct usb_device *udev

struct usb_device pointer

const char *module_name

should be filled with KBUILD_MODNAME

struct module *owner

struct module pointer THIS_MODULE for the driver. THIS_MODULE is null for a built-in driver. It is safe even when THIS_MODULE is null.

Description

This interface should be called to allocate a Media Device when multiple drivers share usb_device and the media device. This interface allocates media_device structure and calls media_device_usb_init() to initialize it.

void media_device_delete(struct media_device *mdev, const char *module_name, struct module *owner)

Release media device. Calls kref_put().

Parameters

struct media_device *mdev

struct media_device pointer

const char *module_name

should be filled with KBUILD_MODNAME

struct module *owner

struct module pointer THIS_MODULE for the driver. THIS_MODULE is null for a built-in driver. It is safe even when THIS_MODULE is null.

Description

This interface should be called to put Media Device Instance kref.