0001 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
0002
0003 .. _media-controller-model:
0004
0005 Media device model
0006 ==================
0007
0008 Discovering a device internal topology, and configuring it at runtime,
0009 is one of the goals of the media controller API. To achieve this,
0010 hardware devices and Linux Kernel interfaces are modelled as graph
0011 objects on an oriented graph. The object types that constitute the graph
0012 are:
0013
0014 - An **entity** is a basic media hardware or software building block.
0015 It can correspond to a large variety of logical blocks such as
0016 physical hardware devices (CMOS sensor for instance), logical
0017 hardware devices (a building block in a System-on-Chip image
0018 processing pipeline), DMA channels or physical connectors.
0019
0020 - An **interface** is a graph representation of a Linux Kernel
0021 userspace API interface, like a device node or a sysfs file that
0022 controls one or more entities in the graph.
0023
0024 - A **pad** is a data connection endpoint through which an entity can
0025 interact with other entities. Data (not restricted to video) produced
0026 by an entity flows from the entity's output to one or more entity
0027 inputs. Pads should not be confused with physical pins at chip
0028 boundaries.
0029
0030 - A **data link** is a point-to-point oriented connection between two
0031 pads, either on the same entity or on different entities. Data flows
0032 from a source pad to a sink pad.
0033
0034 - An **interface link** is a point-to-point bidirectional control
0035 connection between a Linux Kernel interface and an entity.
0036
0037 - An **ancillary link** is a point-to-point connection denoting that two
0038 entities form a single logical unit. For example this could represent the
0039 fact that a particular camera sensor and lens controller form a single
0040 physical module, meaning this lens controller drives the lens for this
0041 camera sensor.
