media: Documentation: Add GS_ROUTING documentation

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@jmondi.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

Documentation/userspace-api/media/v4l/dev-subdev.rst

@@ -29,6 +29,8 @@ 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.
 

Documentation/userspace-api/media/v4l/user-func.rst

@@ -70,6 +70,7 @@ Function Reference
     vidioc-subdev-g-crop
     vidioc-subdev-g-fmt
     vidioc-subdev-g-frame-interval
+    vidioc-subdev-g-routing
     vidioc-subdev-g-selection
     vidioc-subdev-querycap
     vidioc-subscribe-event

Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst

+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: V4L
+
+.. _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:macro:: VIDIOC_SUBDEV_G_ROUTING
+
+``int ioctl(int fd, VIDIOC_SUBDEV_G_ROUTING, struct v4l2_subdev_routing *argp)``
+
+.. c:macro:: VIDIOC_SUBDEV_S_ROUTING
+
+``int ioctl(int fd, VIDIOC_SUBDEV_S_ROUTING, struct v4l2_subdev_routing *argp)``
+
+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 in a media entity.
+The routing configuration determines the flows of data inside an entity.
+
+Drivers report their current routing tables using the
+``VIDIOC_SUBDEV_G_ROUTING`` ioctl and application may enable or disable routes
+with the ``VIDIOC_SUBDEV_S_ROUTING`` ioctl, by adding or removing routes and
+setting or clearing flags of the  ``flags`` field of a
+struct :c:type:`v4l2_subdev_route`.
+
+All stream configurations are reset when ``VIDIOC_SUBDEV_S_ROUTING`` is called. This
+means that the userspace must reconfigure all streams after calling the ioctl
+with e.g. ``VIDIOC_SUBDEV_S_FMT``.
+
+Only subdevices which have both sink and source pads can support routing.
+
+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
+value of the ``num_routes`` field. 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
+
+    * - __u32
+      - ``which``
+      - Format to modified, from enum
+        :ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`.
+    * - 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_pad``
+      - Source pad number.
+    * - __u32
+      - ``source_stream``
+      - Source 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.
+
+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 application provided ``num_routes`` is not big enough to contain
+   all the available routes the subdevice exposes.
+
+EINVAL
+   The sink or source pad identifiers reference a non-existing pad, or reference
+   pads of different types (ie. the sink_pad identifiers refers to a source pad)
+   or the sink or source stream identifiers reference a non-existing stream on
+   the sink or source pad.
+
+E2BIG
+   The application provided ``num_routes`` for ``VIDIOC_SUBDEV_S_ROUTING`` is
+   larger than the number of routes the driver can handle.