To describe in the kernel the connection between devices and their supporting peripherals (for example, a camera sensor and the vcm driving the focusing lens for it), add a new type of media link to introduce the concept of these ancillary links. Add some elements to the uAPI documentation to explain the new link type, their purpose and some aspects of their current implementation. Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Daniel Scally <djrscally@gmail.com> Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
41 lines
1.8 KiB
ReStructuredText
41 lines
1.8 KiB
ReStructuredText
.. 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. |