Add documentation for VIDIOC_SUBDEV_G/S_ROUTING ioctl and add
description of multiplexed media pads and internal routing to the
V4L2-subdev documentation section.
Signed-off-by: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
---
Documentation/media/uapi/v4l/dev-subdev.rst | 90 +++++++++++
Documentation/media/uapi/v4l/user-func.rst | 1 +
.../uapi/v4l/vidioc-subdev-g-routing.rst | 142 ++++++++++++++++++
3 files changed, 233 insertions(+)
create mode 100644 Documentation/media/uapi/v4l/vidioc-subdev-g-routing.rst
diff --git a/Documentation/media/uapi/v4l/dev-subdev.rst b/Documentation/media/uapi/v4l/dev-subdev.rst
index 2c2768c7343b..b9fbb5d2caec 100644
--- a/Documentation/media/uapi/v4l/dev-subdev.rst
+++ b/Documentation/media/uapi/v4l/dev-subdev.rst
@@ -36,6 +36,8 @@ will feature a character device node on which ioctls can be called to
- 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.
@@ -461,3 +463,91 @@ source pads.
:maxdepth: 1
subdev-formats
+
+
+Multiplexed media pads and internal routing
+-------------------------------------------
+
+Subdevice drivers might expose the internal connections between media pads of an
+entity by providing a routing table that applications can inspect and manipulate
+to change the internal routing between sink and source pads' data connection
+endpoints. A routing table is described by a struct
+:c:type:`v4l2_subdev_routing`, which contains ``num_routes`` route entries, each
+one represented by a struct :c:type:`v4l2_subdev_route`.
+
+Data routes do not just connect one pad to another in an entity, but they refer
+instead to the ``streams`` a media pad provides. Streams are data connection
+endpoints in a media pad. Multiplexed media pads expose multiple ``streams``
+which represent, when the underlying hardware technology allows that, logical
+data streams transported over a single physical media bus.
+
+One of the most notable examples of logical stream multiplexing techniques is
+represented by the data interleaving mechanism implemented by mean of Virtual
+Channels identifiers as defined by the MIPI CSI-2 media bus specifications. A
+subdevice that implements support for Virtual Channel data interleaving might
+expose up to 4 data ``streams``, one for each available Virtual Channel, on the
+source media pad that represents a CSI-2 connection endpoint.
+
+Routes are defined as potential data connections between a ``(sink_pad,
+sink_stream)`` pair and a ``(source_pad, source_stream)`` one, where
+``sink_pad`` and ``source_pad`` are the indexes of two media pads part of the
+same media entity, and ``sink_stream`` and ``source_stream`` are the identifiers
+of the data streams to be connected in the media pads. Media pads that do not
+support data multiplexing expose a single stream, usually with identifier 0.
+
+Routes are reported to applications in a routing table which can be
+inspected and manipulated using the :ref:`routing <VIDIOC_SUBDEV_G_ROUTING>`
+ioctls.
+
+Routes can be activated and deactivated by setting or clearing the
+V4L2_SUBDEV_ROUTE_FL_ACTIVE flag in the ``flags`` field of struct
+:c:type:`v4l2_subdev_route`.
+
+Subdev driver might create routes that cannot be modified by applications. Such
+routes are identified by the presence of the V4L2_SUBDEV_ROUTE_FL_IMMUTABLE
+flag in the ``flags`` field of struct :c:type:`v4l2_subdev_route`.
+
+As an example, the routing table of a source pad which supports two logical
+video streams and can be connected to two sink pads is here below described.
+
+.. flat-table::
+ :widths: 1 2 1
+
+ * - Pad Index
+ - Function
+ - Number of streams
+ * - 0
+ - SINK
+ - 1
+ * - 1
+ - SINK
+ - 1
+ * - 2
+ - SOURCE
+ - 2
+
+In such an example, the source media pad will report a routing table with 4
+entries, one entry for each possible ``(sink_pad, sink_stream) - (source_pad,
+source_stream)`` combination.
+
+.. flat-table:: routing table
+ :widths: 2 1 2
+
+ * - Sink Pad/Sink Stream
+ - ->
+ - Source Pad/Source Stream
+ * - 0/0
+ - ->
+ - 2/0
+ * - 0/0
+ - ->
+ - 2/1
+ * - 1/0
+ - ->
+ - 2/0
+ * - 1/0
+ - ->
+ - 2/1
+
+Subdev drivers are free to decide how many routes an application can enable on
+a media pad at the same time, and refuse to enable or disable specific routes.
diff --git a/Documentation/media/uapi/v4l/user-func.rst b/Documentation/media/uapi/v4l/user-func.rst
index ca0ef21d77fe..0166446f4ab4 100644
--- a/Documentation/media/uapi/v4l/user-func.rst
+++ b/Documentation/media/uapi/v4l/user-func.rst
@@ -77,6 +77,7 @@ Function Reference
vidioc-subdev-g-crop
vidioc-subdev-g-fmt
vidioc-subdev-g-frame-interval
+ vidioc-subdev-g-routing
vidioc-subdev-g-selection
vidioc-subscribe-event
func-mmap
diff --git a/Documentation/media/uapi/v4l/vidioc-subdev-g-routing.rst b/Documentation/media/uapi/v4l/vidioc-subdev-g-routing.rst
new file mode 100644
index 000000000000..8b592722c477
--- /dev/null
+++ b/Documentation/media/uapi/v4l/vidioc-subdev-g-routing.rst
@@ -0,0 +1,142 @@
+.. Permission is granted to copy, distribute and/or modify this
+.. document under the terms of the GNU Free Documentation License,
+.. Version 1.1 or any later version published by the Free Software
+.. Foundation, with no Invariant Sections, no Front-Cover Texts
+.. and no Back-Cover Texts. A copy of the license is included at
+.. Documentation/media/uapi/fdl-appendix.rst.
+..
+.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _VIDIOC_SUBDEV_G_ROUTING:
+
+******************************************************
+ioctl VIDIOC_SUBDEV_G_ROUTING, VIDIOC_SUBDEV_S_ROUTING
+******************************************************
+
+Name
+====
+
+VIDIOC_SUBDEV_G_ROUTING - VIDIOC_SUBDEV_S_ROUTING - Get or set routing between streams of media pads in a media entity.
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_G_ROUTING, struct v4l2_subdev_routing *argp )
+ :name: VIDIOC_SUBDEV_G_ROUTING
+
+.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_S_ROUTING, struct v4l2_subdev_routing *argp )
+ :name: VIDIOC_SUBDEV_S_ROUTING
+
+
+Arguments
+=========
+
+``fd``
+ File descriptor returned by :ref:`open() <func-open>`.
+
+``argp``
+ Pointer to struct :c:type:`v4l2_subdev_routing`.
+
+
+Description
+===========
+
+These ioctls are used to get and set the routing informations associated to
+media pads in a media entity. Routing informations are used to enable or disable
+data connections between stream endpoints of multiplexed media pads.
+
+Drivers report their routing tables using VIDIOC_SUBDEV_G_ROUTING and
+application use the information there reported to enable or disable data
+connections between streams in a pad, by setting or clearing the
+V4L2_SUBDEV_ROUTE_FL_ACTIVE flag of ``flags`` field of a struct
+:c:type:`v4l2_subdev_route`.
+
+When inspecting routes through VIDIOC_SUBDEV_G_ROUTING and the application
+provided ``num_routes`` is not big enough to contain all the available routes
+the subdevice exposes, drivers return the ENOSPC error code and adjust the
+``num_routes`` value. Application should then reserve enough memory for all the
+route entries and call VIDIOC_SUBDEV_G_ROUTING again.
+
+.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
+
+.. c:type:: v4l2_subdev_routing
+
+.. flat-table:: struct v4l2_subdev_routing
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 2
+
+ * - struct :c:type:`v4l2_subdev_route`
+ - ``routes[]``
+ - Array of struct :c:type:`v4l2_subdev_route` entries
+ * - __u32
+ - ``num_routes``
+ - Number of entries of the routes array
+ * - __u32
+ - ``reserved``\ [5]
+ - Reserved for future extensions. Applications and drivers must set
+ the array to zero.
+
+.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
+
+.. c:type:: v4l2_subdev_route
+
+.. flat-table:: struct v4l2_subdev_route
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 2
+
+ * - __u32
+ - ``sink_pad``
+ - Sink pad number
+ * - __u32
+ - ``sink_stream``
+ - Sink pad stream number
+ * - __u32
+ - ``source_stream``
+ - Source pad stream number
+ * - __u32
+ - ``sink_stream``
+ - Sink pad stream number
+ * - __u32
+ - ``flags``
+ - Route enable/disable flags
+ :ref:`v4l2_subdev_routing_flags <v4l2-subdev-routing-flags>`.
+ * - __u32
+ - ``reserved``\ [5]
+ - Reserved for future extensions. Applications and drivers must set
+ the array to zero.
+
+.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
+
+.. _v4l2-subdev-routing-flags:
+
+.. flat-table:: enum v4l2_subdev_routing_flags
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 3 1 4
+
+ * - V4L2_SUBDEV_ROUTE_FL_ACTIVE
+ - 0
+ - The route is enabled. Set by applications.
+ * - V4L2_SUBDEV_ROUTE_FL_IMMUTABLE
+ - 1
+ - The route is immutable. Set by the driver.
+
+Return Value
+============
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.
+
+ENOSPC
+ The number of provided route entries is less than the available ones.
+
+EINVAL
+ The sink or source pad identifiers reference a non-existing pad, or refernce
+ pads of different types (ie. the sink_pad identifiers refers to a source pad)
+ The sink or source stream identifiers reference a non-existing stream
+ in the sink or source pad.
+
--
2.20.1
