• Laurent Pinchart's avatar
    [media] media: Entities, pads and links · 53e269c1
    Laurent Pinchart authored
    As video hardware pipelines become increasingly complex and
    configurable, the current hardware description through v4l2 subdevices
    reaches its limits. In addition to enumerating and configuring
    subdevices, video camera drivers need a way to discover and modify at
    runtime how those subdevices are connected. This is done through new
    elements called entities, pads and links.
    
    An entity is a basic media hardware building block. It can correspond to
    a large variety of logical blocks such as physical hardware devices
    (CMOS sensor for instance), logical hardware devices (a building block
    in a System-on-Chip image processing pipeline), DMA channels or physical
    connectors.
    
    A pad is a connection endpoint through which an entity can interact with
    other entities. Data (not restricted to video) produced by an entity
    flows from the entity's output to one or more entity inputs. Pads should
    not be confused with physical pins at chip boundaries.
    
    A link is a point-to-point oriented connection between two pads, either
    on the same entity or on different entities. Data flows from a source
    pad to a sink pad.
    
    Links are stored in the source entity. To make backwards graph walk
    faster, a copy of all links is also stored in the sink entity. The copy
    is known as a backlink and is only used to help graph traversal.
    
    The entity API is made of three functions:
    
    - media_entity_init() initializes an entity. The caller must provide an
    array of pads as well as an estimated number of links. The links array
    is allocated dynamically and will be reallocated if it grows beyond the
    initial estimate.
    
    - media_entity_cleanup() frees resources allocated for an entity. It
    must be called during the cleanup phase after unregistering the entity
    and before freeing it.
    
    - media_entity_create_link() creates a link between two entities. An
    entry in the link array of each entity is allocated and stores pointers
    to source and sink pads.
    
    When a media device is unregistered, all its entities are unregistered
    automatically.
    
    The code is based on Hans Verkuil <hverkuil@xs4all.nl> initial work.
    Signed-off-by: default avatarLaurent Pinchart <laurent.pinchart@ideasonboard.com>
    Signed-off-by: default avatarSakari Ailus <sakari.ailus@iki.fi>
    Acked-by: default avatarHans Verkuil <hverkuil@xs4all.nl>
    Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@redhat.com>
    53e269c1
Makefile 298 Bytes