1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2
3.. _media-controller-model:
4
5Media device model
6==================
7
8Discovering a device internal topology, and configuring it at runtime,
9is one of the goals of the media controller API. To achieve this,
10hardware devices and Linux Kernel interfaces are modelled as graph
11objects on an oriented graph. The object types that constitute the graph
12are:
13
14-  An **entity** is a basic media hardware or software building block.
15   It can correspond to a large variety of logical blocks such as
16   physical hardware devices (CMOS sensor for instance), logical
17   hardware devices (a building block in a System-on-Chip image
18   processing pipeline), DMA channels or physical connectors.
19
20-  An **interface** is a graph representation of a Linux Kernel
21   userspace API interface, like a device node or a sysfs file that
22   controls one or more entities in the graph.
23
24-  A **pad** is a data connection endpoint through which an entity can
25   interact with other entities. Data (not restricted to video) produced
26   by an entity flows from the entity's output to one or more entity
27   inputs. Pads should not be confused with physical pins at chip
28   boundaries.
29
30-  A **data link** is a point-to-point oriented connection between two
31   pads, either on the same entity or on different entities. Data flows
32   from a source pad to a sink pad.
33
34-  An **interface link** is a point-to-point bidirectional control
35   connection between a Linux Kernel interface and an entity.
36
37- An **ancillary link** is a point-to-point connection denoting that two
38  entities form a single logical unit. For example this could represent the
39  fact that a particular camera sensor and lens controller form a single
40  physical module, meaning this lens controller drives the lens for this
41  camera sensor.