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+.. -*- coding: utf-8; mode: rst -*-
+
+.. _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.