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

[Kieran Bingham <kieran.bingham@ideasonboard.com>]

Quoting Kieran Bingham (2022-02-03 10:55:05)
> 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?

Aha, now I see in the next patch that it only really applies to the
G_ROUTING.

But it might be worth noting that if -ENOSPC is returned, num_routes is
set to the number of routes required by the kernel.

--
Kieran


> 
> 
> 
> > +
> > +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
> >