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.