4. Media Controller devices¶

4.1. 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.

4.1.1. 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.

4.1.2. 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().

4.1.3. 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().

4.1.4. 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().

4.1.5. 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.

4.1.6. Links¶

Links are represented by a struct media_link instance, defined in include/media/media-entity.h. There are two types of links:

1. pad to pad links:

Associate two entities via their PADs. Each entity has a list that points to all links originating at or targeting any of its pads. A given link is thus stored twice, once in the source entity and once in the target entity.

Drivers create pad to pad links by calling: media_create_pad_link() and remove with media_entity_remove_links().

2. interface to entity links:

Associate one interface to a Link.

Drivers create interface to entity links by calling: media_create_intf_link() and remove with media_remove_intf_links().

Note

Links can only be created after having both ends already created.

Links have flags that describe the link capabilities and state. The valid values are described at media_create_pad_link() and media_create_intf_link().

4.1.7. 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().

4.1.8. 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.

4.1.9. Links setup¶

Link properties can be modified at runtime by calling media_entity_setup_link().

4.1.10. 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.

4.1.11. Link validation¶

Link validation is performed by media_pipeline_start() for any entity which has sink pads in the pipeline. The media_entity.link_validate() callback is used for that purpose. In link_validate() callback, entity driver should check that the properties of the source pad of the connected entity and its own sink pad match. It is up to the type of the entity (and in the end, the properties of the hardware) what matching actually means.

Subsystems should facilitate link validation by providing subsystem specific helper functions to provide easy access for commonly needed information, and in the end provide a way to use driver-specific callbacks.

4.1.12. 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.

4.1.13. 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 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

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.
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 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.

enum media_gobj_type¶: type of a graph object

Constants

MEDIA_GRAPH_ENTITY: Identify a media entity
MEDIA_GRAPH_PAD: Identify a media pad
MEDIA_GRAPH_LINK: Identify a media link
MEDIA_GRAPH_INTF_DEVNODE: Identify a media Kernel API interface via a device node

struct media_gobj¶: Define a graph object.

Definition

struct media_gobj {
  struct media_device     *mdev;
  u32 id;
  struct list_head        list;
};

Members

mdev: Pointer to the struct media_device that owns the object
id: Non-zero object ID identifier. The ID should be unique inside a media_device, as it is composed by MEDIA_BITS_PER_TYPE to store the type plus MEDIA_BITS_PER_ID to store the ID
list: List entry stored in one of the per-type mdev object lists

Description

All objects on the media graph should have this struct embedded

struct media_entity_enum¶: An enumeration of media entities.

Definition

struct media_entity_enum {
  unsigned long *bmap;
  int idx_max;
};

Members

bmap: Bit map in which each bit represents one entity at struct media_entity->internal_idx.
idx_max: Number of bits in bmap

struct media_graph¶: Media graph traversal state

Definition

struct media_graph {
  struct {
    struct media_entity *entity;
    struct list_head *link;
  } stack[MEDIA_ENTITY_ENUM_MAX_DEPTH];
  struct media_entity_enum ent_enum;
  int top;
};

Members

stack: Graph traversal stack; the stack contains information on the path the media entities to be walked and the links through which they were reached.
stack.entity: pointer to struct media_entity at the graph.
stack.link: pointer to struct list_head.
ent_enum: Visited entities
top: The top of the stack

struct media_pipeline¶: Media pipeline related information

Definition

struct media_pipeline {
  int streaming_count;
  struct media_graph graph;
};

Members

streaming_count: Streaming start count - streaming stop count
graph: Media graph walk during pipeline start / stop

struct media_link¶: A link object part of a media graph.

Definition

struct media_link {
  struct media_gobj graph_obj;
  struct list_head list;
  union {
    struct media_gobj *gobj0;
    struct media_pad *source;
    struct media_interface *intf;
  };
  union {
    struct media_gobj *gobj1;
    struct media_pad *sink;
    struct media_entity *entity;
  };
  struct media_link *reverse;
  unsigned long flags;
  bool is_backlink;
};

Members

graph_obj: Embedded structure containing the media object common data
list: Linked list associated with an entity or an interface that owns the link.
{unnamed_union}: anonymous
gobj0: Part of a union. Used to get the pointer for the first graph_object of the link.
source: Part of a union. Used only if the first object (gobj0) is a pad. In that case, it represents the source pad.
intf: Part of a union. Used only if the first object (gobj0) is an interface.
{unnamed_union}: anonymous
gobj1: Part of a union. Used to get the pointer for the second graph_object of the link.
sink: Part of a union. Used only if the second object (gobj1) is a pad. In that case, it represents the sink pad.
entity: Part of a union. Used only if the second object (gobj1) is an entity.
reverse: Pointer to the link for the reverse direction of a pad to pad link.
flags: Link flags, as defined in uapi/media.h (MEDIA_LNK_FL_*)
is_backlink: Indicate if the link is a backlink.

enum media_pad_signal_type¶: type of the signal inside a media pad

Constants

PAD_SIGNAL_DEFAULT: Default signal. Use this when all inputs or all outputs are uniquely identified by the pad number.
PAD_SIGNAL_ANALOG: The pad contains an analog signal. It can be Radio Frequency, Intermediate Frequency, a baseband signal or sub-cariers. Tuner inputs, IF-PLL demodulators, composite and s-video signals should use it.
PAD_SIGNAL_DV: Contains a digital video signal, with can be a bitstream of samples taken from an analog TV video source. On such case, it usually contains the VBI data on it.
PAD_SIGNAL_AUDIO: Contains an Intermediate Frequency analog signal from an audio sub-carrier or an audio bitstream. IF signals are provided by tuners and consumed by audio AM/FM decoders. Bitstream audio is provided by an audio decoder.

struct media_pad¶: A media pad graph object.

Definition

struct media_pad {
  struct media_gobj graph_obj;
  struct media_entity *entity;
  u16 index;
  enum media_pad_signal_type sig_type;
  unsigned long flags;
};

Members

graph_obj: Embedded structure containing the media object common data
entity: Entity this pad belongs to
index: Pad index in the entity pads array, numbered from 0 to n
sig_type: Type of the signal inside a media pad
flags: Pad flags, as defined in include/uapi/linux/media.h (seek for MEDIA_PAD_FL_*)

struct media_entity_operations¶: Media entity operations

Definition

struct media_entity_operations {
  int (*get_fwnode_pad)(struct fwnode_endpoint *endpoint);
  int (*link_setup)(struct media_entity *entity,const struct media_pad *local, const struct media_pad *remote, u32 flags);
  int (*link_validate)(struct media_link *link);
};

Members

get_fwnode_pad: Return the pad number based on a fwnode endpoint or a negative value on error. This operation can be used to map a fwnode to a media pad number. Optional.
link_setup: Notify the entity of link changes. The operation can return an error, in which case link setup will be cancelled. Optional.
link_validate: Return whether a link is valid from the entity point of view. The media_pipeline_start() function validates all links by calling this operation. Optional.

Description

Note

Those these callbacks are called with struct media_device.graph_mutex mutex held.

enum media_entity_type¶: Media entity type

Constants

MEDIA_ENTITY_TYPE_BASE: The entity isn’t embedded in another subsystem structure.
MEDIA_ENTITY_TYPE_VIDEO_DEVICE: The entity is embedded in a struct video_device instance.
MEDIA_ENTITY_TYPE_V4L2_SUBDEV: The entity is embedded in a struct v4l2_subdev instance.

Description

Media entity objects are often not instantiated directly, but the media entity structure is inherited by (through embedding) other subsystem-specific structures. The media entity type identifies the type of the subclass structure that implements a media entity instance.

This allows runtime type identification of media entities and safe casting to the correct object type. For instance, a media entity structure instance embedded in a v4l2_subdev structure instance will have the type MEDIA_ENTITY_TYPE_V4L2_SUBDEV and can safely be cast to a v4l2_subdev structure using the container_of() macro.

struct media_entity¶: A media entity graph object.

Definition

struct media_entity {
  struct media_gobj graph_obj;
  const char *name;
  enum media_entity_type obj_type;
  u32 function;
  unsigned long flags;
  u16 num_pads;
  u16 num_links;
  u16 num_backlinks;
  int internal_idx;
  struct media_pad *pads;
  struct list_head links;
  const struct media_entity_operations *ops;
  int stream_count;
  int use_count;
  struct media_pipeline *pipe;
  union {
    struct {
      u32 major;
      u32 minor;
    } dev;
  } info;
};

Members

graph_obj: Embedded structure containing the media object common data.
name: Entity name.
obj_type: Type of the object that implements the media_entity.
function: Entity main function, as defined in include/uapi/linux/media.h (seek for MEDIA_ENT_F_*)
flags: Entity flags, as defined in include/uapi/linux/media.h (seek for MEDIA_ENT_FL_*)
num_pads: Number of sink and source pads.
num_links: Total number of links, forward and back, enabled and disabled.
num_backlinks: Number of backlinks
internal_idx: An unique internal entity specific number. The numbers are re-used if entities are unregistered or registered again.
pads: Pads array with the size defined by num_pads.
links: List of data links.
ops: Entity operations.
stream_count: Stream count for the entity.
use_count: Use count for the entity.
pipe: Pipeline this entity belongs to.
info: Union with devnode information. Kept just for backward compatibility.
info.dev: Contains device major and minor info.
info.dev.major: device node major, if the device is a devnode.
info.dev.minor: device node minor, if the device is a devnode.

Description

Note

stream_count and use_count reference counts must never be negative, but are signed integers on purpose: a simple WARN_ON(<0) check can be used to detect reference count bugs that would make them negative.

struct media_interface¶: A media interface graph object.

Definition

struct media_interface {
  struct media_gobj               graph_obj;
  struct list_head                links;
  u32 type;
  u32 flags;
};

Members

graph_obj: embedded graph object
links: List of links pointing to graph entities
type: Type of the interface as defined in include/uapi/linux/media.h (seek for MEDIA_INTF_T_*)
flags: Interface flags as defined in include/uapi/linux/media.h (seek for MEDIA_INTF_FL_*)

Description

Note

Currently, no flags for media_interface is defined.

struct media_intf_devnode¶: A media interface via a device node.

Definition

struct media_intf_devnode {
  struct media_interface          intf;
  u32 major;
  u32 minor;
};

Members

intf: embedded interface object
major: Major number of a device node
minor: Minor number of a device node

u32 media_entity_id(struct media_entity * entity)¶: return the media entity graph object id

Parameters

struct media_entity * entity: pointer to media_entity

enum media_gobj_type media_type(struct media_gobj * gobj)¶: return the media object type

Parameters

struct media_gobj * gobj: Pointer to the struct media_gobj graph object

u32 media_id(struct media_gobj * gobj)¶: return the media object ID

Parameters

struct media_gobj * gobj: Pointer to the struct media_gobj graph object

u32 media_gobj_gen_id(enum media_gobj_type type, u64 local_id)¶: encapsulates type and ID on at the object ID

Parameters

enum media_gobj_type type: object type as define at enum media_gobj_type.
u64 local_id: next ID, from struct media_device.id.

bool is_media_entity_v4l2_video_device(struct media_entity * entity)¶: Check if the entity is a video_device

Parameters

struct media_entity * entity: pointer to entity

Return

true if the entity is an instance of a video_device object and can safely be cast to a struct video_device using the container_of() macro, or false otherwise.

bool is_media_entity_v4l2_subdev(struct media_entity * entity)¶: Check if the entity is a v4l2_subdev

Parameters

struct media_entity * entity: pointer to entity

Return

true if the entity is an instance of a v4l2_subdev object and can safely be cast to a struct v4l2_subdev using the container_of() macro, or false otherwise.

int __media_entity_enum_init(struct media_entity_enum * ent_enum, int idx_max)¶: Initialise an entity enumeration

Parameters

struct media_entity_enum * ent_enum: Entity enumeration to be initialised
int idx_max: Maximum number of entities in the enumeration

Return

Returns zero on success or a negative error code.

void media_entity_enum_cleanup(struct media_entity_enum * ent_enum)¶: Release resources of an entity enumeration

Parameters

struct media_entity_enum * ent_enum: Entity enumeration to be released

void media_entity_enum_zero(struct media_entity_enum * ent_enum)¶: Clear the entire enum

Parameters

struct media_entity_enum * ent_enum: Entity enumeration to be cleared

void media_entity_enum_set(struct media_entity_enum * ent_enum, struct media_entity * entity)¶: Mark a single entity in the enum

Parameters

struct media_entity_enum * ent_enum: Entity enumeration
struct media_entity * entity: Entity to be marked

void media_entity_enum_clear(struct media_entity_enum * ent_enum, struct media_entity * entity)¶: Unmark a single entity in the enum

Parameters

struct media_entity_enum * ent_enum: Entity enumeration
struct media_entity * entity: Entity to be unmarked

bool media_entity_enum_test(struct media_entity_enum * ent_enum, struct media_entity * entity)¶: Test whether the entity is marked

Parameters

struct media_entity_enum * ent_enum: Entity enumeration
struct media_entity * entity: Entity to be tested

Description

Returns true if the entity was marked.

bool media_entity_enum_test_and_set(struct media_entity_enum * ent_enum, struct media_entity * entity)¶: Test whether the entity is marked, and mark it

Parameters

struct media_entity_enum * ent_enum: Entity enumeration
struct media_entity * entity: Entity to be tested

Description

Returns true if the entity was marked, and mark it before doing so.

bool media_entity_enum_empty(struct media_entity_enum * ent_enum)¶: Test whether the entire enum is empty

Parameters

struct media_entity_enum * ent_enum: Entity enumeration

Return

true if the entity was empty.

bool media_entity_enum_intersects(struct media_entity_enum * ent_enum1, struct media_entity_enum * ent_enum2)¶: Test whether two enums intersect

Parameters

struct media_entity_enum * ent_enum1: First entity enumeration
struct media_entity_enum * ent_enum2: Second entity enumeration

Return

true if entity enumerations ent_enum1 and ent_enum2 intersect, otherwise false.

gobj_to_entity(gobj)¶: returns the struct media_entity pointer from the gobj contained on it.

Parameters

gobj: Pointer to the struct media_gobj graph object

gobj_to_pad(gobj)¶: returns the struct media_pad pointer from the gobj contained on it.

Parameters

gobj: Pointer to the struct media_gobj graph object

gobj_to_link(gobj)¶: returns the struct media_link pointer from the gobj contained on it.

Parameters

gobj: Pointer to the struct media_gobj graph object

gobj_to_intf(gobj)¶: returns the struct media_interface pointer from the gobj contained on it.

Parameters

gobj: Pointer to the struct media_gobj graph object

intf_to_devnode(intf)¶: returns the struct media_intf_devnode pointer from the intf contained on it.

Parameters

intf: Pointer to struct media_intf_devnode

void media_gobj_create(struct media_device * mdev, enum media_gobj_type type, struct media_gobj * gobj)¶: Initialize a graph object

Parameters

struct media_device * mdev: Pointer to the media_device that contains the object
enum media_gobj_type type: Type of the object
struct media_gobj * gobj: Pointer to the struct media_gobj graph object

Description

This routine initializes the embedded struct media_gobj inside a media graph object. It is called automatically if media_*_create function calls are used. However, if the object (entity, link, pad, interface) is embedded on some other object, this function should be called before registering the object at the media controller.

void media_gobj_destroy(struct media_gobj * gobj)¶: Stop using a graph object on a media device

Parameters

struct media_gobj * gobj: Pointer to the struct media_gobj graph object

Description

This should be called by all routines like media_device_unregister() that remove/destroy media graph objects.

int media_entity_pads_init(struct media_entity * entity, u16 num_pads, struct media_pad * pads)¶: Initialize the entity pads

Parameters

struct media_entity * entity: entity where the pads belong
u16 num_pads: total number of sink and source pads
struct media_pad * pads: Array of num_pads pads.

Description

The pads array is managed by the entity driver and passed to media_entity_pads_init() where its pointer will be stored in the media_entity structure.

If no pads are needed, drivers could either directly fill media_entity->num_pads with 0 and media_entity->pads with NULL or call this function that will do the same.

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_pads_init(). The function will initialize the other pads fields.

void media_entity_cleanup(struct media_entity * entity)¶: free resources associated with an entity

Parameters

struct media_entity * entity: entity where the pads belong

Description

This function must be called during the cleanup phase after unregistering the entity (currently, it does nothing).

int media_get_pad_index(struct media_entity * entity, bool is_sink, enum media_pad_signal_type sig_type)¶: retrieves a pad index from an entity

Parameters

struct media_entity * entity: entity where the pads belong
bool is_sink: true if the pad is a sink, false if it is a source
enum media_pad_signal_type sig_type: type of signal of the pad to be search

Description

This helper function finds the first pad index inside an entity that satisfies both is_sink and sig_type conditions.

Return

On success, return the pad number. If the pad was not found or the media entity is a NULL pointer, return -EINVAL.

int media_create_pad_link(struct media_entity * source, u16 source_pad, struct media_entity * sink, u16 sink_pad, u32 flags)¶: creates a link between two entities.

Parameters

struct media_entity * source: pointer to media_entity of the source pad.
u16 source_pad: number of the source pad in the pads array
struct media_entity * sink: pointer to media_entity of the sink pad.
u16 sink_pad: number of the sink pad in the pads array.
u32 flags: Link flags, as defined in include/uapi/linux/media.h ( seek for MEDIA_LNK_FL_*)

Description

Valid values for flags:

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.

Note

Before calling this function, media_entity_pads_init() and media_device_register_entity() should be called previously for both ends.

int media_create_pad_links(const struct media_device * mdev, const u32 source_function, struct media_entity * source, const u16 source_pad, const u32 sink_function, struct media_entity * sink, const u16 sink_pad, u32 flags, const bool allow_both_undefined)¶: creates a link between two entities.

Parameters

const struct media_device * mdev: Pointer to the media_device that contains the object
const u32 source_function: Function of the source entities. Used only if source is NULL.
struct media_entity * source: pointer to media_entity of the source pad. If NULL, it will use all entities that matches the sink_function.
const u16 source_pad: number of the source pad in the pads array
const u32 sink_function: Function of the sink entities. Used only if sink is NULL.
struct media_entity * sink: pointer to media_entity of the sink pad. If NULL, it will use all entities that matches the sink_function.
const u16 sink_pad: number of the sink pad in the pads array.
u32 flags: Link flags, as defined in include/uapi/linux/media.h.
const bool allow_both_undefined: if true, then both source and sink can be NULL. In such case, it will create a crossbar between all entities that matches source_function to all entities that matches sink_function. If false, it will return 0 and won’t create any link if both source and sink are NULL.

Description

Valid values for flags:

A MEDIA_LNK_FL_ENABLED flag indicates that the link is enabled and can be: used to transfer media data. If multiple links are created and this flag is passed as an argument, only the first created link will have this flag.
A MEDIA_LNK_FL_IMMUTABLE flag 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.

It is common for some devices to have multiple source and/or sink entities of the same type that should be linked. While media_create_pad_link() creates link by link, this function is meant to allow 1:n, n:1 and even cross-bar (n:n) links.

Note

Before calling this function, media_entity_pads_init() and media_device_register_entity() should be called previously for the entities to be linked.

void media_entity_remove_links(struct media_entity * entity)¶: remove all links associated with an entity

Parameters

struct media_entity * entity: pointer to media_entity

Description

Note

This is called automatically when an entity is unregistered via media_device_register_entity().

int __media_entity_setup_link(struct media_link * link, u32 flags)¶: Configure a media link without locking

Parameters

struct media_link * link: The link being configured
u32 flags: Link configuration flags

Description

The bulk of link setup is handled by the two entities connected through the link. This function notifies both entities of the link configuration change.

If the link is immutable or if the current and new configuration are identical, return immediately.

The user is expected to hold link->source->parent->mutex. If not, media_entity_setup_link() should be used instead.

int media_entity_setup_link(struct media_link * link, u32 flags)¶: changes the link flags properties in runtime

Parameters

struct media_link * link: pointer to media_link
u32 flags: the requested new link flags

Description

The only configurable property is the MEDIA_LNK_FL_ENABLED link flag flag to enable/disable a link. Links marked with the MEDIA_LNK_FL_IMMUTABLE link flag can not be enabled or disabled.

When a link is enabled or disabled, the media framework calls the link_setup operation for the two entities at the source and sink of the link, in that order. If the second link_setup call fails, another link_setup call is made on the first entity to restore the original link flags.

Media device drivers can be notified of link setup operations by setting the media_device.link_notify pointer to a callback function. If provided, the notification callback will be called before enabling and after disabling links.

Entity drivers must implement the link_setup operation if any of their links is non-immutable. The operation must either configure the hardware or store the configuration information to be applied later.

Link configuration must not have any side effect on other links. If an enabled link at a sink pad prevents another link at the same pad from being enabled, the link_setup operation must return -EBUSY and can’t implicitly disable the first enabled link.

Note

The valid values of the flags for the link is the same as described on media_create_pad_link(), for pad to pad links or the same as described on media_create_intf_link(), for interface to entity links.

struct media_link * media_entity_find_link(struct media_pad * source, struct media_pad * sink)¶: Find a link between two pads

Parameters

struct media_pad * source: Source pad
struct media_pad * sink: Sink pad

Return

returns a pointer to the link between the two entities. If no such link exists, return NULL.

struct media_pad * media_entity_remote_pad(const struct media_pad * pad)¶: Find the pad at the remote end of a link

Parameters

const struct media_pad * pad: Pad at the local end of the link

Description

Search for a remote pad connected to the given pad by iterating over all links originating or terminating at that pad until an enabled link is found.

Return

returns a pointer to the pad at the remote end of the first found enabled link, or NULL if no enabled link has been found.

int media_entity_get_fwnode_pad(struct media_entity * entity, struct fwnode_handle * fwnode, unsigned long direction_flags)¶: Get pad number from fwnode

Parameters

struct media_entity * entity: The entity
struct fwnode_handle * fwnode: Pointer to the fwnode_handle which should be used to find the pad
unsigned long direction_flags: Expected direction of the pad, as defined in include/uapi/linux/media.h (seek for MEDIA_PAD_FL_*)

Description

This function can be used to resolve the media pad number from a fwnode. This is useful for devices which use more complex mappings of media pads.

If the entity does not implement the get_fwnode_pad() operation then this function searches the entity for the first pad that matches the direction_flags.

Return

returns the pad number on success or a negative error code.

int media_graph_walk_init(struct media_graph * graph, struct media_device * mdev)¶: Allocate resources used by graph walk.

Parameters

struct media_graph * graph: Media graph structure that will be used to walk the graph
struct media_device * mdev: Pointer to the media_device that contains the object

void media_graph_walk_cleanup(struct media_graph * graph)¶: Release resources used by graph walk.

Parameters

struct media_graph * graph: Media graph structure that will be used to walk the graph

void media_graph_walk_start(struct media_graph * graph, struct media_entity * entity)¶: Start walking the media graph at a given entity

Parameters

struct media_graph * graph: Media graph structure that will be used to walk the graph
struct media_entity * entity: Starting entity

Description

Before using this function, media_graph_walk_init() must be used to allocate resources used for walking the graph. This function initializes the graph traversal structure to walk the entities graph starting at the given entity. The traversal structure must not be modified by the caller during graph traversal. After the graph walk, the resources must be released using media_graph_walk_cleanup().

struct media_entity * media_graph_walk_next(struct media_graph * graph)¶: Get the next entity in the graph

Parameters

struct media_graph * graph: Media graph structure

Description

Perform a depth-first traversal of the given media entities graph.

The graph structure must have been previously initialized with a call to media_graph_walk_start().

Return

returns the next entity in the graph or NULL if the whole graph have been traversed.

int media_pipeline_start(struct media_entity * entity, struct media_pipeline * pipe)¶: Mark a pipeline as streaming

Parameters

struct media_entity * entity: Starting entity
struct media_pipeline * pipe: Media pipeline to be assigned to all entities in the pipeline.

Description

Mark all entities connected to a given entity through enabled links, either directly or indirectly, as streaming. The given pipeline object is assigned to every entity in the pipeline and stored in the media_entity pipe field.

Calls to this function can be nested, in which case the same number of media_pipeline_stop() calls will be required to stop streaming. The pipeline pointer must be identical for all nested calls to media_pipeline_start().

int __media_pipeline_start(struct media_entity * entity, struct media_pipeline * pipe)¶: Mark a pipeline as streaming

Parameters

struct media_entity * entity: Starting entity
struct media_pipeline * pipe: Media pipeline to be assigned to all entities in the pipeline.

Description

..note:: This is the non-locking version of media_pipeline_start()

void media_pipeline_stop(struct media_entity * entity)¶: Mark a pipeline as not streaming

Parameters

struct media_entity * entity: Starting entity

Description

Mark all entities connected to a given entity through enabled links, either directly or indirectly, as not streaming. The media_entity pipe field is reset to NULL.

If multiple calls to media_pipeline_start() have been made, the same number of calls to this function are required to mark the pipeline as not streaming.

void __media_pipeline_stop(struct media_entity * entity)¶: Mark a pipeline as not streaming

Parameters

struct media_entity * entity: Starting entity

Description

Note

This is the non-locking version of media_pipeline_stop()

struct media_intf_devnode * media_devnode_create(struct media_device * mdev, u32 type, u32 flags, u32 major, u32 minor)¶: creates and initializes a device node interface

Parameters

struct media_device * mdev: pointer to struct media_device
u32 type: type of the interface, as given by include/uapi/linux/media.h ( seek for MEDIA_INTF_T_*) macros.
u32 flags: Interface flags, as defined in include/uapi/linux/media.h ( seek for MEDIA_INTF_FL_*)
u32 major: Device node major number.
u32 minor: Device node minor number.

Return

if succeeded, returns a pointer to the newly allocated: media_intf_devnode pointer.

Note

Currently, no flags for media_interface is defined.

void media_devnode_remove(struct media_intf_devnode * devnode)¶: removes a device node interface

Parameters

struct media_intf_devnode * devnode: pointer to media_intf_devnode to be freed.

Description

When a device node interface is removed, all links to it are automatically removed.

media_create_intf_link(struct media_entity * entity, struct media_interface * intf, u32 flags)¶: creates a link between an entity and an interface

Parameters

struct media_entity * entity: pointer to media_entity
struct media_interface * intf: pointer to media_interface
u32 flags: Link flags, as defined in include/uapi/linux/media.h ( seek for MEDIA_LNK_FL_*)

Description

Valid values for flags:

MEDIA_LNK_FL_ENABLED

Indicates that the interface is connected to the entity hardware. That’s the default value for interfaces. An interface may be disabled if the hardware is busy due to the usage of some other interface that it is currently controlling the hardware.

A typical example is an hybrid TV device that handle only one type of stream on a given time. So, when the digital TV is streaming, the V4L2 interfaces won’t be enabled, as such device is not able to also stream analog TV or radio.

Note

Before calling this function, media_devnode_create() should be called for the interface and media_device_register_entity() should be called for the interface that will be part of the link.

void __media_remove_intf_link(struct media_link * link)¶: remove a single interface link

Parameters

struct media_link * link: pointer to media_link.

Description

Note

This is an unlocked version of media_remove_intf_link()

void media_remove_intf_link(struct media_link * link)¶: remove a single interface link

Parameters

struct media_link * link: pointer to media_link.

Description

Note

Prefer to use this one, instead of __media_remove_intf_link()

void __media_remove_intf_links(struct media_interface * intf)¶: remove all links associated with an interface

Parameters

struct media_interface * intf: pointer to media_interface

Description

Note

This is an unlocked version of media_remove_intf_links().

void media_remove_intf_links(struct media_interface * intf)¶: remove all links associated with an interface

Parameters

struct media_interface * intf: pointer to media_interface

Description

Note

This is called automatically when an entity is unregistered via media_device_register_entity() and by media_devnode_remove().
Prefer to use this one, instead of __media_remove_intf_links().

media_entity_call(entity, operation, args…)¶: Calls a struct media_entity_operations operation on an entity

Parameters

entity: entity where the operation will be called
operation: type of the operation. Should be the name of a member of struct media_entity_operations.
args...: variable arguments

Description

This helper function will check if operation is not NULL. On such case, it will issue a call to operation(entity, args).

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.