.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. _media-controller-model:
Media device model
==================
Discovering a device internal topology, and configuring it at runtime,
is one of the goals of the media controller API. To achieve this,
hardware devices and Linux Kernel interfaces are modelled as graph
objects on an oriented graph. The object types that constitute the graph
are:
- An **entity** is a basic media hardware or software 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.
- An **interface** is a graph representation of a Linux Kernel
userspace API interface, like a device node or a sysfs file that
controls one or more entities in the graph.
- A **pad** is a data 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 **data 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.
- An **interface link** is a point-to-point bidirectional control
connection between a Linux Kernel interface and an entity.
- An **ancillary link** is a point-to-point connection denoting that two
entities form a single logical unit. For example this could represent the
fact that a particular camera sensor and lens controller form a single
physical module, meaning this lens controller drives the lens for this
camera sensor.
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