mirror of
https://github.com/Fishwaldo/Star64_linux.git
synced 2025-03-17 12:44:10 +00:00
media: Documentation: Update documentation for streams
Document how streams interacts with formats and selections. Update documentation in respect to what is allowed, in particular streams are only supported via full routes, source-only routes are not supported right now. The centerpiece of the API additions are streams. Albeit routes are configured via S_ROUTING IOCTL that also declares streams, it is streams that are accessed through other APIs. Thus refer to streams instead of routes in documentation. Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
This commit is contained in:
parent
9037d1308b
commit
58388bd700
1 changed files with 55 additions and 29 deletions
|
@ -406,6 +406,8 @@ pixel array is not rectangular but cross-shaped or round. The maximum
|
|||
size may also be smaller than the BOUNDS rectangle.
|
||||
|
||||
|
||||
.. _format-propagation:
|
||||
|
||||
Order of configuration and format propagation
|
||||
---------------------------------------------
|
||||
|
||||
|
@ -507,12 +509,12 @@ source pads.
|
|||
Streams, multiplexed media pads and internal routing
|
||||
----------------------------------------------------
|
||||
|
||||
Commonly V4L2 subdevices support only separate video streams, that is, only a
|
||||
single stream can pass through a media link and a media pad. Thus each pad
|
||||
contains a format configuration for that single stream. In some cases a subdev
|
||||
can do stream processing and split a stream into two or compose two streams
|
||||
into one, but the inputs and outputs for the subdev are still a single stream
|
||||
per pad.
|
||||
Simple V4L2 sub-devices do not support multiple, unrelated video streams,
|
||||
and only a single stream can pass through a media link and a media pad.
|
||||
Thus each pad contains a format and selection configuration for that
|
||||
single stream. A subdev can do stream processing and split a stream into
|
||||
two or compose two streams into one, but the inputs and outputs for the
|
||||
subdev are still a single stream per pad.
|
||||
|
||||
Some hardware, e.g. MIPI CSI-2, support multiplexed streams, that is, multiple
|
||||
data streams are transmitted on the same bus, which is represented by a media
|
||||
|
@ -535,38 +537,62 @@ Understanding streams
|
|||
A stream is a stream of content (e.g. pixel data or metadata) flowing through
|
||||
the media pipeline from a source (e.g. a sensor) towards the final sink (e.g. a
|
||||
receiver and demultiplexer in a SoC). Each media link carries all the enabled
|
||||
streams from one end of the link to the other, and subdevices have routing
|
||||
streams from one end of the link to the other, and sub-devices have routing
|
||||
tables which describe how the incoming streams from sink pads are routed to the
|
||||
source pads.
|
||||
|
||||
A stream ID (often just "stream") is a media link-local identifier for a stream.
|
||||
In other words, a particular stream ID must exist on both sides of a media
|
||||
A stream ID is a media pad-local identifier for a stream. Streams IDs of
|
||||
the same stream must be equal on both ends of a link. In other words,
|
||||
a particular stream ID must exist on both sides of a media
|
||||
link, but another stream ID can be used for the same stream at the other side
|
||||
of the subdevice.
|
||||
of the sub-device.
|
||||
|
||||
A stream at a specific point in the media pipeline is identified with the
|
||||
subdev and a (pad, stream) pair. For subdevices that do not support
|
||||
multiplexed streams the 'stream' is always 0.
|
||||
A stream at a specific point in the media pipeline is identified by the
|
||||
sub-device and a (pad, stream) pair. For sub-devices that do not support
|
||||
multiplexed streams the 'stream' field is always 0.
|
||||
|
||||
Interaction between routes, streams, formats and selections
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
The addition of streams to the V4L2 sub-device interface moves the sub-device
|
||||
formats and selections from pads to (pad, stream) pairs. Besides the
|
||||
usual pad, also the stream ID needs to be provided for setting formats and
|
||||
selections. The order of configuring formats and selections along a stream is
|
||||
the same as without streams (see :ref:`format-propagation`).
|
||||
|
||||
Instead of the sub-device wide merging of streams from all sink pads
|
||||
towards all source pads, data flows for each route are separate from each
|
||||
other. Any number of routes from streams on sink pads towards streams on
|
||||
source pads is allowed, to the extent supported by drivers. For every
|
||||
stream on a source pad, however, only a single route is allowed.
|
||||
|
||||
Any configurations of a stream within a pad, such as format or selections,
|
||||
are independent of similar configurations on other streams. This is
|
||||
subject to change in the future.
|
||||
|
||||
Configuring streams
|
||||
^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
The configuration of the streams is done individually for each subdevice and
|
||||
the validity of the streams between subdevices is validated when the pipeline
|
||||
The configuration of the streams is done individually for each sub-device and
|
||||
the validity of the streams between sub-devices is validated when the pipeline
|
||||
is started.
|
||||
|
||||
There are three steps in configuring the streams:
|
||||
|
||||
1) Set up links. Connect the pads between subdevices using the :ref:`Media
|
||||
1) Set up links. Connect the pads between sub-devices using the :ref:`Media
|
||||
Controller API <media_controller>`
|
||||
|
||||
2) Routing. The routing table for the subdevice must be set with
|
||||
2) Streams. Streams are declared and their routing is configured by
|
||||
setting the routing table for the sub-device using
|
||||
:ref:`VIDIOC_SUBDEV_S_ROUTING <VIDIOC_SUBDEV_G_ROUTING>` ioctl. Note that
|
||||
setting the routing table will reset all the stream configurations in a media
|
||||
entity.
|
||||
setting the routing table will reset formats and selections in the
|
||||
sub-device to default values.
|
||||
|
||||
3) Configure streams. Each route endpoint must be configured
|
||||
with :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>`.
|
||||
3) Configure formats and selections. Formats and selections of each stream
|
||||
are configured separately as documented for plain sub-devices in
|
||||
:ref:`format-propagation`. The stream ID is set to the same stream ID
|
||||
associated with either sink or source pads of routes configured using the
|
||||
:ref:`VIDIOC_SUBDEV_S_ROUTING <VIDIOC_SUBDEV_G_ROUTING>` ioctl.
|
||||
|
||||
Multiplexed streams setup example
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
@ -586,7 +612,7 @@ A simple example of a multiplexed stream setup might be as follows:
|
|||
- DMA Engines in the SoC (DMA Engine), one for each stream. Each DMA engine is
|
||||
connected to a single source pad in the receiver.
|
||||
|
||||
The sensors, the bridge and the receiver are modeled as V4L2 subdevices,
|
||||
The sensors, the bridge and the receiver are modeled as V4L2 sub-devices,
|
||||
exposed to userspace via /dev/v4l-subdevX device nodes. The DMA engines are
|
||||
modeled as V4L2 devices, exposed to userspace via /dev/videoX nodes.
|
||||
|
||||
|
@ -596,7 +622,7 @@ To configure this pipeline, the userspace must take the following steps:
|
|||
bridge to the receiver, and the receiver to the DMA engines. This step does
|
||||
not differ from normal non-multiplexed media controller setup.
|
||||
|
||||
2) Configure routing.
|
||||
2) Configure routing
|
||||
|
||||
.. flat-table:: Bridge routing table
|
||||
:header-rows: 1
|
||||
|
@ -630,14 +656,14 @@ not differ from normal non-multiplexed media controller setup.
|
|||
- V4L2_SUBDEV_ROUTE_FL_ACTIVE
|
||||
- Pixel data stream from Sensor B
|
||||
|
||||
3) Configure streams
|
||||
3) Configure formats and selections
|
||||
|
||||
After configuring the routing table, the next step is configuring the streams.
|
||||
This step is similar to configuring the pads in a non-multiplexed streams
|
||||
setup, with the difference that we need to configure each (pad, stream) pair
|
||||
(i.e. route endpoint) instead of just a pad.
|
||||
After configuring routing, the next step is configuring the formats and
|
||||
selections for the streams. This is similar to performing this step without
|
||||
streams, with just one exception: the ``stream`` field needs to be assigned
|
||||
to the value of the stream ID.
|
||||
|
||||
A common way to accomplish this is to start from the sensors and propagate the
|
||||
configurations along the stream towards the receiver,
|
||||
using :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>` ioctls to configure each
|
||||
stream endpoint in each subdev.
|
||||
stream endpoint in each sub-device.
|
||||
|
|
Loading…
Add table
Reference in a new issue