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@@ -53,4 +53,24 @@
implementing policies that belong to userspace.</para>
<para>The media controller API aims at solving those problems.</para>
</section>
+
+ <section id="media-controller-model">
+ <title>Media device model</title>
+ <para>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 are modelled as an oriented graph of building blocks called entities
+ connected through pads.</para>
+ <para>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.</para>
+ <para>A pad is a 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.</para>
+ <para>A 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.</para>
+ </section>
</chapter>

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