Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 669 insertions, 0 deletions

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+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+
+.. _subdev:
+
+********************
+Sub-device Interface
+********************
+
+The complex nature of V4L2 devices, where hardware is often made of
+several integrated circuits that need to interact with each other in a
+controlled way, leads to complex V4L2 drivers. The drivers usually
+reflect the hardware model in software, and model the different hardware
+components as software blocks called sub-devices.
+
+V4L2 sub-devices are usually kernel-only objects. If the V4L2 driver
+implements the media device API, they will automatically inherit from
+media entities. Applications will be able to enumerate the sub-devices
+and discover the hardware topology using the media entities, pads and
+links enumeration API.
+
+In addition to make sub-devices discoverable, drivers can also choose to
+make them directly configurable by applications. When both the
+sub-device driver and the V4L2 device driver support this, sub-devices
+will feature a character device node on which ioctls can be called to
+
+-  query, read and write sub-devices controls
+
+-  subscribe and unsubscribe to events and retrieve them
+
+-  negotiate image formats on individual pads
+
+-  inspect and modify internal data routing between pads of the same entity
+
+Sub-device character device nodes, conventionally named
+``/dev/v4l-subdev*``, use major number 81.
+
+Drivers may opt to limit the sub-device character devices to only expose
+operations that do not modify the device state. In such a case the sub-devices
+are referred to as ``read-only`` in the rest of this documentation, and the
+related restrictions are documented in individual ioctls.
+
+
+Controls
+========
+
+Most V4L2 controls are implemented by sub-device hardware. Drivers
+usually merge all controls and expose them through video device nodes.
+Applications can control all sub-devices through a single interface.
+
+Complex devices sometimes implement the same control in different pieces
+of hardware. This situation is common in embedded platforms, where both
+sensors and image processing hardware implement identical functions,
+such as contrast adjustment, white balance or faulty pixels correction.
+As the V4L2 controls API doesn't support several identical controls in a
+single device, all but one of the identical controls are hidden.
+
+Applications can access those hidden controls through the sub-device
+node with the V4L2 control API described in :ref:`control`. The ioctls
+behave identically as when issued on V4L2 device nodes, with the
+exception that they deal only with controls implemented in the
+sub-device.
+
+Depending on the driver, those controls might also be exposed through
+one (or several) V4L2 device nodes.
+
+
+Events
+======
+
+V4L2 sub-devices can notify applications of events as described in
+:ref:`event`. The API behaves identically as when used on V4L2 device
+nodes, with the exception that it only deals with events generated by
+the sub-device. Depending on the driver, those events might also be
+reported on one (or several) V4L2 device nodes.
+
+
+.. _pad-level-formats:
+
+Pad-level Formats
+=================
+
+.. warning::
+
+    Pad-level formats are only applicable to very complex devices that
+    need to expose low-level format configuration to user space. Generic
+    V4L2 applications do *not* need to use the API described in this
+    section.
+
+.. note::
+
+    For the purpose of this section, the term *format* means the
+    combination of media bus data format, frame width and frame height.
+
+Image formats are typically negotiated on video capture and output
+devices using the format and
+:ref:`selection <VIDIOC_SUBDEV_G_SELECTION>` ioctls. The driver is
+responsible for configuring every block in the video pipeline according
+to the requested format at the pipeline input and/or output.
+
+For complex devices, such as often found in embedded systems, identical
+image sizes at the output of a pipeline can be achieved using different
+hardware configurations. One such example is shown on
+:ref:`pipeline-scaling`, where image scaling can be performed on both
+the video sensor and the host image processing hardware.
+
+
+.. _pipeline-scaling:
+
+.. kernel-figure:: pipeline.dot
+    :alt:   pipeline.dot
+    :align: center
+
+    Image Format Negotiation on Pipelines
+
+    High quality and high speed pipeline configuration
+
+
+
+The sensor scaler is usually of less quality than the host scaler, but
+scaling on the sensor is required to achieve higher frame rates.
+Depending on the use case (quality vs. speed), the pipeline must be
+configured differently. Applications need to configure the formats at
+every point in the pipeline explicitly.
+
+Drivers that implement the :ref:`media API <media-controller-intro>`
+can expose pad-level image format configuration to applications. When
+they do, applications can use the
+:ref:`VIDIOC_SUBDEV_G_FMT <VIDIOC_SUBDEV_G_FMT>` and
+:ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>` ioctls. to
+negotiate formats on a per-pad basis.
+
+Applications are responsible for configuring coherent parameters on the
+whole pipeline and making sure that connected pads have compatible
+formats. The pipeline is checked for formats mismatch at
+:ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` time, and an ``EPIPE`` error
+code is then returned if the configuration is invalid.
+
+Pad-level image format configuration support can be tested by calling
+the :ref:`VIDIOC_SUBDEV_G_FMT` ioctl on pad
+0. If the driver returns an ``EINVAL`` error code pad-level format
+configuration is not supported by the sub-device.
+
+
+Format Negotiation
+------------------
+
+Acceptable formats on pads can (and usually do) depend on a number of
+external parameters, such as formats on other pads, active links, or
+even controls. Finding a combination of formats on all pads in a video
+pipeline, acceptable to both application and driver, can't rely on
+formats enumeration only. A format negotiation mechanism is required.
+
+Central to the format negotiation mechanism are the get/set format
+operations. When called with the ``which`` argument set to
+:ref:`V4L2_SUBDEV_FORMAT_TRY <VIDIOC_SUBDEV_G_FMT>`, the
+:ref:`VIDIOC_SUBDEV_G_FMT <VIDIOC_SUBDEV_G_FMT>` and
+:ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>` ioctls operate on
+a set of formats parameters that are not connected to the hardware
+configuration. Modifying those 'try' formats leaves the device state
+untouched (this applies to both the software state stored in the driver
+and the hardware state stored in the device itself).
+
+While not kept as part of the device state, try formats are stored in
+the sub-device file handles. A
+:ref:`VIDIOC_SUBDEV_G_FMT <VIDIOC_SUBDEV_G_FMT>` call will return
+the last try format set *on the same sub-device file handle*. Several
+applications querying the same sub-device at the same time will thus not
+interact with each other.
+
+To find out whether a particular format is supported by the device,
+applications use the
+:ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>` ioctl. Drivers
+verify and, if needed, change the requested ``format`` based on device
+requirements and return the possibly modified value. Applications can
+then choose to try a different format or accept the returned value and
+continue.
+
+Formats returned by the driver during a negotiation iteration are
+guaranteed to be supported by the device. In particular, drivers
+guarantee that a returned format will not be further changed if passed
+to an :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>` call as-is
+(as long as external parameters, such as formats on other pads or links'
+configuration are not changed).
+
+Drivers automatically propagate formats inside sub-devices. When a try
+or active format is set on a pad, corresponding formats on other pads of
+the same sub-device can be modified by the driver. Drivers are free to
+modify formats as required by the device. However, they should comply
+with the following rules when possible:
+
+-  Formats should be propagated from sink pads to source pads. Modifying
+   a format on a source pad should not modify the format on any sink
+   pad.
+
+-  Sub-devices that scale frames using variable scaling factors should
+   reset the scale factors to default values when sink pads formats are
+   modified. If the 1:1 scaling ratio is supported, this means that
+   source pads formats should be reset to the sink pads formats.
+
+Formats are not propagated across links, as that would involve
+propagating them from one sub-device file handle to another.
+Applications must then take care to configure both ends of every link
+explicitly with compatible formats. Identical formats on the two ends of
+a link are guaranteed to be compatible. Drivers are free to accept
+different formats matching device requirements as being compatible.
+
+:ref:`sample-pipeline-config` shows a sample configuration sequence
+for the pipeline described in :ref:`pipeline-scaling` (table columns
+list entity names and pad numbers).
+
+
+.. raw:: latex
+
+    \begingroup
+    \scriptsize
+    \setlength{\tabcolsep}{2pt}
+
+.. tabularcolumns:: |p{2.0cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|
+
+.. _sample-pipeline-config:
+
+.. flat-table:: Sample Pipeline Configuration
+    :header-rows:  1
+    :stub-columns: 0
+    :widths: 5 5 5 5 5 5 5
+
+    * -
+      - Sensor/0
+
+        format
+      - Frontend/0
+
+        format
+      - Frontend/1
+
+        format
+      - Scaler/0
+
+        format
+      - Scaler/0
+
+        compose selection rectangle
+      - Scaler/1
+
+        format
+    * - Initial state
+      - 2048x1536
+
+        SGRBG8_1X8
+      - (default)
+      - (default)
+      - (default)
+      - (default)
+      - (default)
+    * - Configure frontend sink format
+      - 2048x1536
+
+        SGRBG8_1X8
+      - *2048x1536*
+
+        *SGRBG8_1X8*
+      - *2046x1534*
+
+        *SGRBG8_1X8*
+      - (default)
+      - (default)
+      - (default)
+    * - Configure scaler sink format
+      - 2048x1536
+
+        SGRBG8_1X8
+      - 2048x1536
+
+        SGRBG8_1X8
+      - 2046x1534
+
+        SGRBG8_1X8
+      - *2046x1534*
+
+        *SGRBG8_1X8*
+      - *0,0/2046x1534*
+      - *2046x1534*
+
+        *SGRBG8_1X8*
+    * - Configure scaler sink compose selection
+      - 2048x1536
+
+        SGRBG8_1X8
+      - 2048x1536
+
+        SGRBG8_1X8
+      - 2046x1534
+
+        SGRBG8_1X8
+      - 2046x1534
+
+        SGRBG8_1X8
+      - *0,0/1280x960*
+      - *1280x960*
+
+        *SGRBG8_1X8*
+
+.. raw:: latex
+
+    \endgroup
+
+1. Initial state. The sensor source pad format is set to its native 3MP
+   size and V4L2_MBUS_FMT_SGRBG8_1X8 media bus code. Formats on the
+   host frontend and scaler sink and source pads have the default
+   values, as well as the compose rectangle on the scaler's sink pad.
+
+2. The application configures the frontend sink pad format's size to
+   2048x1536 and its media bus code to V4L2_MBUS_FMT_SGRBG_1X8. The
+   driver propagates the format to the frontend source pad.
+
+3. The application configures the scaler sink pad format's size to
+   2046x1534 and the media bus code to V4L2_MBUS_FMT_SGRBG_1X8 to
+   match the frontend source size and media bus code. The media bus code
+   on the sink pad is set to V4L2_MBUS_FMT_SGRBG_1X8. The driver
+   propagates the size to the compose selection rectangle on the
+   scaler's sink pad, and the format to the scaler source pad.
+
+4. The application configures the size of the compose selection
+   rectangle of the scaler's sink pad 1280x960. The driver propagates
+   the size to the scaler's source pad format.
+
+When satisfied with the try results, applications can set the active
+formats by setting the ``which`` argument to
+``V4L2_SUBDEV_FORMAT_ACTIVE``. Active formats are changed exactly as try
+formats by drivers. To avoid modifying the hardware state during format
+negotiation, applications should negotiate try formats first and then
+modify the active settings using the try formats returned during the
+last negotiation iteration. This guarantees that the active format will
+be applied as-is by the driver without being modified.
+
+
+.. _v4l2-subdev-selections:
+
+Selections: cropping, scaling and composition
+---------------------------------------------
+
+Many sub-devices support cropping frames on their input or output pads
+(or possible even on both). Cropping is used to select the area of
+interest in an image, typically on an image sensor or a video decoder.
+It can also be used as part of digital zoom implementations to select
+the area of the image that will be scaled up.
+
+Crop settings are defined by a crop rectangle and represented in a
+struct :c:type:`v4l2_rect` by the coordinates of the top
+left corner and the rectangle size. Both the coordinates and sizes are
+expressed in pixels.
+
+As for pad formats, drivers store try and active rectangles for the
+selection targets :ref:`v4l2-selections-common`.
+
+On sink pads, cropping is applied relative to the current pad format.
+The pad format represents the image size as received by the sub-device
+from the previous block in the pipeline, and the crop rectangle
+represents the sub-image that will be transmitted further inside the
+sub-device for processing.
+
+The scaling operation changes the size of the image by scaling it to new
+dimensions. The scaling ratio isn't specified explicitly, but is implied
+from the original and scaled image sizes. Both sizes are represented by
+struct :c:type:`v4l2_rect`.
+
+Scaling support is optional. When supported by a subdev, the crop
+rectangle on the subdev's sink pad is scaled to the size configured
+using the
+:ref:`VIDIOC_SUBDEV_S_SELECTION <VIDIOC_SUBDEV_G_SELECTION>` IOCTL
+using ``V4L2_SEL_TGT_COMPOSE`` selection target on the same pad. If the
+subdev supports scaling but not composing, the top and left values are
+not used and must always be set to zero.
+
+On source pads, cropping is similar to sink pads, with the exception
+that the source size from which the cropping is performed, is the
+COMPOSE rectangle on the sink pad. In both sink and source pads, the
+crop rectangle must be entirely contained inside the source image size
+for the crop operation.
+
+The drivers should always use the closest possible rectangle the user
+requests on all selection targets, unless specifically told otherwise.
+``V4L2_SEL_FLAG_GE`` and ``V4L2_SEL_FLAG_LE`` flags may be used to round
+the image size either up or down. :ref:`v4l2-selection-flags`
+
+
+Types of selection targets
+--------------------------
+
+
+Actual targets
+^^^^^^^^^^^^^^
+
+Actual targets (without a postfix) reflect the actual hardware
+configuration at any point of time. There is a BOUNDS target
+corresponding to every actual target.
+
+
+BOUNDS targets
+^^^^^^^^^^^^^^
+
+BOUNDS targets is the smallest rectangle that contains all valid actual
+rectangles. It may not be possible to set the actual rectangle as large
+as the BOUNDS rectangle, however. This may be because e.g. a sensor's
+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
+---------------------------------------------
+
+Inside subdevs, the order of image processing steps will always be from
+the sink pad towards the source pad. This is also reflected in the order
+in which the configuration must be performed by the user: the changes
+made will be propagated to any subsequent stages. If this behaviour is
+not desired, the user must set ``V4L2_SEL_FLAG_KEEP_CONFIG`` flag. This
+flag causes no propagation of the changes are allowed in any
+circumstances. This may also cause the accessed rectangle to be adjusted
+by the driver, depending on the properties of the underlying hardware.
+
+The coordinates to a step always refer to the actual size of the
+previous step. The exception to this rule is the sink compose
+rectangle, which refers to the sink compose bounds rectangle --- if it
+is supported by the hardware.
+
+1. Sink pad format. The user configures the sink pad format. This format
+   defines the parameters of the image the entity receives through the
+   pad for further processing.
+
+2. Sink pad actual crop selection. The sink pad crop defines the crop
+   performed to the sink pad format.
+
+3. Sink pad actual compose selection. The size of the sink pad compose
+   rectangle defines the scaling ratio compared to the size of the sink
+   pad crop rectangle. The location of the compose rectangle specifies
+   the location of the actual sink compose rectangle in the sink compose
+   bounds rectangle.
+
+4. Source pad actual crop selection. Crop on the source pad defines crop
+   performed to the image in the sink compose bounds rectangle.
+
+5. Source pad format. The source pad format defines the output pixel
+   format of the subdev, as well as the other parameters with the
+   exception of the image width and height. Width and height are defined
+   by the size of the source pad actual crop selection.
+
+Accessing any of the above rectangles not supported by the subdev will
+return ``EINVAL``. Any rectangle referring to a previous unsupported
+rectangle coordinates will instead refer to the previous supported
+rectangle. For example, if sink crop is not supported, the compose
+selection will refer to the sink pad format dimensions instead.
+
+
+.. _subdev-image-processing-crop:
+
+.. kernel-figure:: subdev-image-processing-crop.svg
+    :alt:   subdev-image-processing-crop.svg
+    :align: center
+
+    **Figure 4.5. Image processing in subdevs: simple crop example**
+
+In the above example, the subdev supports cropping on its sink pad. To
+configure it, the user sets the media bus format on the subdev's sink
+pad. Now the actual crop rectangle can be set on the sink pad --- the
+location and size of this rectangle reflect the location and size of a
+rectangle to be cropped from the sink format. The size of the sink crop
+rectangle will also be the size of the format of the subdev's source
+pad.
+
+
+.. _subdev-image-processing-scaling-multi-source:
+
+.. kernel-figure:: subdev-image-processing-scaling-multi-source.svg
+    :alt:   subdev-image-processing-scaling-multi-source.svg
+    :align: center
+
+    **Figure 4.6. Image processing in subdevs: scaling with multiple sources**
+
+In this example, the subdev is capable of first cropping, then scaling
+and finally cropping for two source pads individually from the resulting
+scaled image. The location of the scaled image in the cropped image is
+ignored in sink compose target. Both of the locations of the source crop
+rectangles refer to the sink scaling rectangle, independently cropping
+an area at location specified by the source crop rectangle from it.
+
+
+.. _subdev-image-processing-full:
+
+.. kernel-figure:: subdev-image-processing-full.svg
+    :alt:    subdev-image-processing-full.svg
+    :align:  center
+
+    **Figure 4.7. Image processing in subdevs: scaling and composition with multiple sinks and sources**
+
+The subdev driver supports two sink pads and two source pads. The images
+from both of the sink pads are individually cropped, then scaled and
+further composed on the composition bounds rectangle. From that, two
+independent streams are cropped and sent out of the subdev from the
+source pads.
+
+
+.. toctree::
+    :maxdepth: 1
+
+    subdev-formats
+
+Streams, multiplexed media pads and internal routing
+----------------------------------------------------
+
+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
+link connecting a transmitter source pad with a sink pad on the receiver. For
+example, a camera sensor can produce two distinct streams, a pixel stream and a
+metadata stream, which are transmitted on the multiplexed data bus, represented
+by a media link which connects the single sensor's source pad with the receiver
+sink pad. The stream-aware receiver will de-multiplex the streams received on
+the its sink pad and allows to route them individually to one of its source
+pads.
+
+Subdevice drivers that support multiplexed streams are compatible with
+non-multiplexed subdev drivers, but, of course, require a routing configuration
+where the link between those two types of drivers contains only a single
+stream.
+
+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 sub-devices have routing
+tables which describe how the incoming streams from sink pads are routed to the
+source pads.
+
+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 sub-device.
+
+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 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 sub-devices using the :ref:`Media
+Controller API <media_controller>`
+
+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 formats and selections in the
+sub-device to default values.
+
+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
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+A simple example of a multiplexed stream setup might be as follows:
+
+- Two identical sensors (Sensor A and Sensor B). Each sensor has a single source
+  pad (pad 0) which carries a pixel data stream.
+
+- Multiplexer bridge (Bridge). The bridge has two sink pads, connected to the
+  sensors (pads 0, 1), and one source pad (pad 2), which outputs two streams.
+
+- Receiver in the SoC (Receiver). The receiver has a single sink pad (pad 0),
+  connected to the bridge, and two source pads (pads 1-2), going to the DMA
+  engine. The receiver demultiplexes the incoming streams to the source pads.
+
+- 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 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.
+
+To configure this pipeline, the userspace must take the following steps:
+
+1) Set up media links between entities: connect the sensors to the bridge,
+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
+
+.. flat-table:: Bridge routing table
+    :header-rows:  1
+
+    * - Sink Pad/Stream
+      - Source Pad/Stream
+      - Routing Flags
+      - Comments
+    * - 0/0
+      - 2/0
+      - V4L2_SUBDEV_ROUTE_FL_ACTIVE
+      - Pixel data stream from Sensor A
+    * - 1/0
+      - 2/1
+      - V4L2_SUBDEV_ROUTE_FL_ACTIVE
+      - Pixel data stream from Sensor B
+
+.. flat-table:: Receiver routing table
+    :header-rows:  1
+
+    * - Sink Pad/Stream
+      - Source Pad/Stream
+      - Routing Flags
+      - Comments
+    * - 0/0
+      - 1/0
+      - V4L2_SUBDEV_ROUTE_FL_ACTIVE
+      - Pixel data stream from Sensor A
+    * - 0/1
+      - 2/0
+      - V4L2_SUBDEV_ROUTE_FL_ACTIVE
+      - Pixel data stream from Sensor B
+
+3) Configure formats and selections
+
+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 sub-device.