Re: [PATCH v10 27/38] media: Documentation: Add GS_ROUTING documentation

From: Kieran Bingham <kieran.bingham@ideasonboard.com>
To: Hans Verkuil <hverkuil-cisco@xs4all.nl>,
	Jacopo Mondi <jacopo+renesas@jmondi.org>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Pratyush Yadav <p.yadav@ti.com>,
	Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>,
	linux-media@vger.kernel.org,
	niklas.soderlund+renesas@ragnatech.se,
	sakari.ailus@linux.intel.com
Cc: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Subject: Re: [PATCH v10 27/38] media: Documentation: Add GS_ROUTING documentation
Date: Thu, 03 Feb 2022 10:55:05 +0000	[thread overview]
Message-ID: <164388570519.655634.6829425640508111816@Monstersaurus> (raw)
In-Reply-To: <20211130141536.891878-28-tomi.valkeinen@ideasonboard.com>

Quoting Tomi Valkeinen (2021-11-30 14:15:25)
> From: Jacopo Mondi <jacopo+renesas@jmondi.org>
> 
> 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>
> ---
>  .../userspace-api/media/v4l/dev-subdev.rst    |   2 +
>  .../userspace-api/media/v4l/user-func.rst     |   1 +
>  .../media/v4l/vidioc-subdev-g-routing.rst     | 150 ++++++++++++++++++
>  3 files changed, 153 insertions(+)
>  create mode 100644 Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
> 
> diff --git a/Documentation/userspace-api/media/v4l/dev-subdev.rst b/Documentation/userspace-api/media/v4l/dev-subdev.rst
> index fd1de0a73a9f..a67c2749089a 100644
> --- a/Documentation/userspace-api/media/v4l/dev-subdev.rst
> +++ b/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.
>  
> diff --git a/Documentation/userspace-api/media/v4l/user-func.rst b/Documentation/userspace-api/media/v4l/user-func.rst
> index 53e604bd7d60..228c1521f190 100644
> --- a/Documentation/userspace-api/media/v4l/user-func.rst
> +++ b/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
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
> new file mode 100644
> index 000000000000..a0d9c79e162f
> --- /dev/null
> +++ b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
> @@ -0,0 +1,150 @@
> +.. 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: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 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 mut reconfigure all streams after calling the ioctl

s/mut/must/

> +with e.g. ``VIDIOC_SUBDEV_S_FMT``.
> +
> +A special case for routing are routes marked with
> +``V4L2_SUBDEV_ROUTE_FL_SOURCE`` flag. These routes are used to describe
> +source endpoints on sensors and the sink fields are unused.
> +
> +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.
> +    * - V4L2_SUBDEV_ROUTE_FL_IMMUTABLE
> +      - 1
> +      - The route is immutable. Set by the driver.
> +    * - V4L2_SUBDEV_ROUTE_FL_SOURCE
> +      - 2
> +      - The route is a source route, and the ``sink_pad`` and ``sink_stream``
> +        fields are unused. 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.

This doesn't sound right. Maybe:

"The number of route entries provided is less than the available
routes on the device."

But presumably this would be opposites for G_ROUTING and S_ROUTING,
where on G_ROUTING the userspace must provide at least as many route
entries as the driver/device has, and on S_ROUTING, they must provide
not more than?

> +
> +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.
> -- 
> 2.25.1
>