diff options
author | Mauro Carvalho Chehab <mchehab@osg.samsung.com> | 2015-12-11 13:06:08 (GMT) |
---|---|---|
committer | Mauro Carvalho Chehab <mchehab@osg.samsung.com> | 2016-01-11 14:19:04 (GMT) |
commit | db7ee32aa1859c155e634a4d5c44b9cff4c9a6e5 (patch) | |
tree | e2e241841877ec3e5fb9fa72048e6bf12d5ba4e5 /include/media/media-device.h | |
parent | f1fd3289e8c2b99cdf5c1c4426a7d28a809159c2 (diff) | |
download | linux-db7ee32aa1859c155e634a4d5c44b9cff4c9a6e5.tar.xz |
[media] media-device.h: Improve documentation and update it
Now that we moved the content of the media-framework.txt into
the kerneldoc documentation, move the per-function specific
documentation to the corresponding functions and clean it up.
It would be good if we had already the markdown kernel-doc
patches merged upstream, but, while we doesn't have it,
let's make it less ugly at device-drivers.xml.
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Diffstat (limited to 'include/media/media-device.h')
-rw-r--r-- | include/media/media-device.h | 429 |
1 files changed, 191 insertions, 238 deletions
diff --git a/include/media/media-device.h b/include/media/media-device.h index 6728528..65fdd44 100644 --- a/include/media/media-device.h +++ b/include/media/media-device.h @@ -33,23 +33,11 @@ /** * DOC: Media Controller * - * Linux kernel media framework - * ============================ - * - * This document describes the Linux kernel media framework, its data structures, - * functions and their usage. - * - * - * Introduction - * ------------ - * - * The media controller API is documented in DocBook format in - * Documentation/DocBook/media/v4l/media-controller.xml. This document will focus + * The media controller userspace API is documented in DocBook format in + * Documentation/DocBook/media/v4l/media-controller.xml. This document focus * on the kernel-side implementation of the media framework. * - * - * Abstract media device model - * --------------------------- + * * 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 @@ -72,195 +60,104 @@ * pad to a sink pad. * * - * Media device - * ------------ + * * Media device: * - * A media device is represented by a struct media_device instance, defined in + * 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 + * 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(). * - * media_device_register(struct media_device *mdev); - * - * The caller is responsible for initializing the media_device structure before - * registration. The following fields must be set: - * - * - dev must point to the parent device (usually a pci_dev, usb_interface or - * platform_device instance). - * - * - 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: - * - * - 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. - * - * - bus_info represents the location of the device in the system as a - * NUL-terminated ASCII string. For PCI/PCIe devices 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. - * - * - hw_revision is the hardware device revision in a driver-specific format. - * When possible the revision should be formatted with the KERNEL_VERSION - * macro. - * - * - driver_version is formatted with the KERNEL_VERSION macro. The version - * minor must be incremented when new features are added to the userspace API - * without breaking binary compatibility. The version major must be - * incremented when binary compatibility is broken. - * - * 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. - * - * Drivers unregister media device instances by calling - * - * media_device_unregister(struct media_device *mdev); - * - * Unregistering a media device that hasn't been registered is *NOT* safe. - * - * - * Entities, pads and links - * ------------------------ + * * Entities, pads and links: * * - Entities * - * Entities are represented by a struct media_entity instance, defined in + * Entities are represented by a struct &media_entity instance, defined in * include/media/media-entity.h. The structure is usually embedded into a * higher-level structure, such as a v4l2_subdev or video_device instance, * although drivers can allocate entities directly. * * Drivers initialize entity pads by calling - * - * media_entity_pads_init(struct media_entity *entity, u16 num_pads, - * struct media_pad *pads); - * - * If no pads are needed, drivers could directly fill entity->num_pads - * with 0 and entity->pads with NULL or to call the above function that - * will do the same. - * - * 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. - * - * 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. - * - * Unlike the number of pads, the total number of links isn't always known in - * advance by the entity driver. As an initial estimate, media_entity_pads_init - * pre-allocates a number of links equal to the number of pads. The links array - * will be reallocated if it grows beyond the initial estimate. + * media_entity_pads_init(). * * Drivers register entities with a media device by calling + * media_device_register_entity() + * and unregistred by calling + * media_device_unregister_entity(). * - * media_device_register_entity(struct media_device *mdev, - * struct media_entity *entity); + * - Interfaces * - * Entities are identified by a unique positive integer ID. Drivers can provide an - * ID by filling the media_entity id field prior to registration, or request the - * media controller framework to assign an ID automatically. Drivers that provide - * IDs manually must ensure that all IDs are unique. IDs are not guaranteed to be - * contiguous even when they are all assigned automatically by the framework. + * 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 unregister entities by calling - * - * media_device_unregister_entity(struct media_entity *entity); - * - * Unregistering an entity will not change the IDs of the other entities, and the - * ID will never be reused for a newly registered entity. - * - * When a media device is unregistered, all its entities are unregistered - * automatically. No manual entities unregistration is then required. - * - * Drivers free resources associated with an entity by calling - * - * media_entity_cleanup(struct media_entity *entity); - * - * This function must be called during the cleanup phase after unregistering the - * entity. Note that the media_entity instance itself must be freed explicitly by - * the driver if required. - * - * Entities have flags that describe the entity capabilities and state. - * - * MEDIA_ENT_FL_DEFAULT indicates the default entity for a given type. - * This can be used to report the default audio and video devices or the - * default camera sensor. - * - * Logical entity groups can be defined by setting the group ID of all member - * entities to the same non-zero value. An entity group serves no purpose in the - * kernel, but is reported to userspace during entities enumeration. - * - * Media device drivers should define groups if several entities are logically - * bound together. Example usages include reporting - * - * - ALSA, VBI and video nodes that carry the same media stream - * - lens and flash controllers associated with a sensor + * Drivers initialize and create device node interfaces by calling + * media_devnode_create() + * and remove them by calling: + * media_devnode_remove(). * * - Pads * - * Pads are represented by a struct media_pad instance, defined in + * Pads are represented by a struct &media_pad instance, defined in * include/media/media-entity.h. Each entity stores its pads in a pads array * managed by the entity driver. Drivers usually embed the array in a * driver-specific structure. * - * Pads are identified by their entity and their 0-based index in the pads array. - * Both information are stored in the media_pad structure, making the media_pad - * pointer the canonical way to store and pass link references. + * Pads are identified by their entity and their 0-based index in the pads + * array. + * Both information are stored in the &media_pad structure, making the + * &media_pad pointer the canonical way to store and pass link references. * * Pads have flags that describe the pad capabilities and state. * - * MEDIA_PAD_FL_SINK indicates that the pad supports sinking data. - * MEDIA_PAD_FL_SOURCE indicates that the pad supports sourcing data. + * %MEDIA_PAD_FL_SINK indicates that the pad supports sinking data. + * %MEDIA_PAD_FL_SOURCE indicates that the pad supports sourcing data. * - * One and only one of MEDIA_PAD_FL_SINK and MEDIA_PAD_FL_SOURCE must be set for - * each pad. + * NOTE: One and only one of %MEDIA_PAD_FL_SINK and %MEDIA_PAD_FL_SOURCE must + * be set for each pad. * * - Links * - * Links are represented by a struct media_link instance, defined in - * include/media/media-entity.h. Each entity stores all links originating at or - * targeting any of its pads in a links array. A given link is thus stored - * twice, once in the source entity and once in the target entity. The array is - * pre-allocated and grows dynamically as needed. + * 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: * - * Drivers create links by calling + * 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. * - * media_create_pad_link(struct media_entity *source, u16 source_pad, - * struct media_entity *sink, u16 sink_pad, - * u32 flags); + * Drivers create pad to pad links by calling: + * media_create_pad_link() and remove with media_entity_remove_links(). * - * An entry in the link array of each entity is allocated and stores pointers - * to source and sink pads. + * 2. interface to entity links: * - * Links have flags that describe the link capabilities and state. + * Associate one interface to a Link. * - * 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. + * Drivers create interface to entity links by calling: + * media_create_intf_link() and remove with media_remove_intf_links(). * + * NOTE: * - * Graph traversal - * --------------- + * 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(). + * + * 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. + * 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; * @@ -279,126 +176,82 @@ * currently defined as 16. * * Drivers initiate a graph traversal by calling - * - * media_entity_graph_walk_start(struct media_entity_graph *graph, - * struct media_entity *entity); + * media_entity_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_entity_graph_walk_next(struct media_entity_graph *graph); + * media_entity_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. + * 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() * - * media_entity_find_link(struct media_pad *source, - * struct media_pad *sink); - * - * media_entity_remote_pad(struct media_pad *pad); - * - * Refer to the kerneldoc documentation for more information. - * - * - * 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 - * media_entity structure includes a use_count field that media drivers can use to - * track the number of users of every entity for power management needs. + * Use count and power handling: * - * The 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. + * Due to the wide differences between drivers regarding power management + * needs, the media controller does not implement power management. However, + * the &media_entity structure 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. * - * Links setup - * ----------- + * Links setup: * * Link properties can be modified at runtime by calling + * media_entity_setup_link() * - * media_entity_setup_link(struct media_link *link, u32 flags); - * - * The flags argument contains the requested new link flags. - * - * The only configurable property is the ENABLED link flag to enable/disable a - * link. Links marked with the 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. - * - * - * Pipelines and media streams - * --------------------------- + * 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_entity_pipeline_start(struct media_entity *entity, - * struct media_pipeline *pipe); + * media_entity_pipeline_start(). * * The function will mark all entities connected to the given entity through * enabled links, either directly or indirectly, as streaming. * - * The media_pipeline instance pointed to by the pipe argument will be stored in - * every entity in the pipeline. Drivers should embed the media_pipeline structure - * in higher-level pipeline structures and can then access the pipeline through - * the media_entity pipe field. + * The &media_pipeline instance pointed to by the pipe argument will be stored + * in every entity in the pipeline. Drivers should embed the &media_pipeline + * structure in higher-level pipeline structures and can then access the + * pipeline through the &media_entity pipe field. * - * Calls to media_entity_pipeline_start() can be nested. The pipeline pointer must - * be identical for all nested calls to the function. + * Calls to media_entity_pipeline_start() can be nested. The pipeline pointer + * must be identical for all nested calls to the function. * * media_entity_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_entity_pipeline_stop(struct media_entity *entity); + * media_entity_pipeline_stop(). * * If multiple calls to media_entity_pipeline_start() have been made the same - * number of media_entity_pipeline_stop() calls are required to stop streaming. The - * media_entity pipe field is reset to NULL on the last nested stop call. + * number of media_entity_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. + * 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. * - * - * Link validation - * --------------- + * Link validation: * * Link validation is performed by media_entity_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 + * &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. @@ -484,13 +337,113 @@ struct media_device { /* media_devnode to media_device */ #define to_media_device(node) container_of(node, struct media_device, devnode) +/** + * __media_device_register() - Registers a media device element + * + * @mdev: pointer to struct &media_device + * @owner: should be filled with %THIS_MODULE + * + * Users, should, instead, call the media_device_register() macro. + * + * The caller is responsible for initializing the media_device structure before + * registration. The following fields must be set: + * + * - dev must point to the parent device (usually a &pci_dev, &usb_interface or + * &platform_device instance). + * + * - 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: + * + * - 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. + * + * - bus_info represents the location of the device in the system as a + * NUL-terminated ASCII string. For PCI/PCIe devices 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. + * + * - hw_revision is the hardware device revision in a driver-specific format. + * When possible the revision should be formatted with the KERNEL_VERSION + * macro. + * + * - driver_version is formatted with the KERNEL_VERSION macro. The version + * minor must be incremented when new features are added to the userspace API + * without breaking binary compatibility. The version major must be + * incremented when binary compatibility is broken. + * + * Notes: + * + * 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. + */ int __must_check __media_device_register(struct media_device *mdev, struct module *owner); #define media_device_register(mdev) __media_device_register(mdev, THIS_MODULE) + +/** + * __media_device_unregister() - Unegisters a media device element + * + * @mdev: pointer to struct &media_device + */ void media_device_unregister(struct media_device *mdev); +/** + * media_device_register_entity() - registers a media entity inside a + * previously registered media device. + * + * @mdev: pointer to struct &media_device + * @entity: pointer to struct &media_entity to be registered + * + * 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. + */ int __must_check media_device_register_entity(struct media_device *mdev, struct media_entity *entity); + +/* + * media_device_unregister_entity() - unregisters a media entity. + * + * @entity: pointer to struct &media_entity to be unregistered + * + * 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. + */ void media_device_unregister_entity(struct media_entity *entity); struct media_device *media_device_get_devres(struct device *dev); struct media_device *media_device_find_devres(struct device *dev); |