Re: [PATCH v5 7/7] media: docs: add documentation for the Extended API

[Alexandre Courbot <acourbot@chromium.org>]

On Wed, Aug 5, 2020 at 4:32 AM Helen Koike <helen.koike@collabora.com> wrote:
>
> Add documentation and update references in current documentation for the
> Extended API.
>
> Signed-off-by: Helen Koike <helen.koike@collabora.com>
> ---
> Changes in v5:
> - new patch
>
>  .../userspace-api/media/v4l/buffer.rst        |   5 +
>  .../userspace-api/media/v4l/common.rst        |   1 +
>  .../userspace-api/media/v4l/dev-capture.rst   |   5 +
>  .../userspace-api/media/v4l/dev-output.rst    |   5 +
>  .../userspace-api/media/v4l/ext-api.rst       | 107 +++++++++
>  .../userspace-api/media/v4l/format.rst        |  16 +-
>  .../userspace-api/media/v4l/user-func.rst     |   5 +
>  .../media/v4l/vidioc-ext-create-bufs.rst      |  95 ++++++++
>  .../media/v4l/vidioc-ext-prepare-buf.rst      |  62 ++++++
>  .../media/v4l/vidioc-ext-qbuf.rst             | 204 ++++++++++++++++++
>  .../media/v4l/vidioc-ext-querybuf.rst         |  79 +++++++
>  .../media/v4l/vidioc-g-ext-pix-fmt.rst        | 117 ++++++++++
>  12 files changed, 697 insertions(+), 4 deletions(-)
>  create mode 100644 Documentation/userspace-api/media/v4l/ext-api.rst
>  create mode 100644 Documentation/userspace-api/media/v4l/vidioc-ext-create-bufs.rst
>  create mode 100644 Documentation/userspace-api/media/v4l/vidioc-ext-prepare-buf.rst
>  create mode 100644 Documentation/userspace-api/media/v4l/vidioc-ext-qbuf.rst
>  create mode 100644 Documentation/userspace-api/media/v4l/vidioc-ext-querybuf.rst
>  create mode 100644 Documentation/userspace-api/media/v4l/vidioc-g-ext-pix-fmt.rst
>
> diff --git a/Documentation/userspace-api/media/v4l/buffer.rst b/Documentation/userspace-api/media/v4l/buffer.rst
> index 57e752aaf414a..c832bedd64e4c 100644
> --- a/Documentation/userspace-api/media/v4l/buffer.rst
> +++ b/Documentation/userspace-api/media/v4l/buffer.rst
> @@ -27,6 +27,11 @@ such as pointers and sizes for each plane, are stored in
>  struct :c:type:`v4l2_plane` instead. In that case,
>  struct :c:type:`v4l2_buffer` contains an array of plane structures.
>
> +.. note::
> +
> +    The :ref:`ext_api` version can also be used, and it is
> +    preferable when applicable.
> +
>  Dequeued video buffers come with timestamps. The driver decides at which
>  part of the frame and with which clock the timestamp is taken. Please
>  see flags in the masks ``V4L2_BUF_FLAG_TIMESTAMP_MASK`` and
> diff --git a/Documentation/userspace-api/media/v4l/common.rst b/Documentation/userspace-api/media/v4l/common.rst
> index 7d81c58a13cd7..3430e0bdad667 100644
> --- a/Documentation/userspace-api/media/v4l/common.rst
> +++ b/Documentation/userspace-api/media/v4l/common.rst
> @@ -59,6 +59,7 @@ applicable to all devices.
>      ext-ctrls-detect
>      fourcc
>      format
> +    ext-api
>      planar-apis
>      selection-api
>      crop
> diff --git a/Documentation/userspace-api/media/v4l/dev-capture.rst b/Documentation/userspace-api/media/v4l/dev-capture.rst
> index 44d3094093ab6..5077639787d92 100644
> --- a/Documentation/userspace-api/media/v4l/dev-capture.rst
> +++ b/Documentation/userspace-api/media/v4l/dev-capture.rst
> @@ -102,6 +102,11 @@ and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, even if :ref:`VIDIOC_S_FMT <VIDIOC
>  requests and always returns default parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does.
>  :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` is optional.
>
> +.. note::
> +
> +    The :ref:`ext_api` version can also be used, and it is
> +    preferable when applicable.
> +
>
>  Reading Images
>  ==============
> diff --git a/Documentation/userspace-api/media/v4l/dev-output.rst b/Documentation/userspace-api/media/v4l/dev-output.rst
> index e4f2a1d8b0fc7..f8f40c708e49f 100644
> --- a/Documentation/userspace-api/media/v4l/dev-output.rst
> +++ b/Documentation/userspace-api/media/v4l/dev-output.rst
> @@ -99,6 +99,11 @@ and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, even if :ref:`VIDIOC_S_FMT <VIDIOC
>  requests and always returns default parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does.
>  :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` is optional.
>
> +.. note::
> +
> +    The :ref:`ext_api` version can also be used, and it is
> +    preferable when applicable.
> +
>
>  Writing Images
>  ==============
> diff --git a/Documentation/userspace-api/media/v4l/ext-api.rst b/Documentation/userspace-api/media/v4l/ext-api.rst
> new file mode 100644
> index 0000000000000..da2a82960d22f
> --- /dev/null
> +++ b/Documentation/userspace-api/media/v4l/ext-api.rst
> @@ -0,0 +1,107 @@
> +.. 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/userspace-api/media/fdl-appendix.rst.
> +..
> +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
> +
> +.. _ext_api:
> +
> +*************
> +Extendend API

s/Extendend/Extended

> +*************
> +
> +Introduction
> +============
> +
> +The Extended Format API was conceived to extend V4L2 capabilities and
> +to simplify certain mechanisms.
> +It unifies single- vs multi- planar handling,
> +brings the concept of pixelformat + modifiers, allows planes to be placed
> +in any offset inside a buffer and let userspace to change colorspace
> +attributes if supported by the driver.
> +
> +Data format negotiation and buffer handling works very similar to the classical
> +version, thus in this document we'll just mention the main differences.
> +
> +Data Format Negotiation
> +=======================
> +
> +The API replaces the classical ioctls:
> +
> +:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`, :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`,
> +:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>`
> +(with :c:type:`v4l2_format` as the main parameter).
> +
> +By the extended versions:
> +
> +:ref:`VIDIOC_G_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>`,
> +:ref:`VIDIOC_S_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>`,
> +:ref:`VIDIOC_TRY_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>`
> +(with :c:type:`v4l2_ext_pix_format` as the main parameter).
> +
> +For CAPTURE and OUTPUT queues only.
> +
> +The ``type`` field of struct :c:type:`v4l2_ext_pix_format` only accepts
> +``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or ``V4L2_BUF_TYPE_VIDEO_OUTPUT``, and it
> +supports multiplanar format through a combination of ``pixelfomat`` and
> +``modifier`` fields.
> +
> +Only the single-planar variants of the pixel formats are valid in the
> +``pixelformat`` field.
> +To support multi-planar, a modifier should be set in the ``modifier`` field to
> +provide more information regarding the memory layout of pixels and number of
> +planes.
> +
> +The ``plane_fmt`` field is an array which holds information by plane using
> +the :c:type:`v4l2_plane_ext_pix_format`. When this struct is filled, its
> +``sizeimage`` field should be non-zero for all valid planes for a given
> +``pixelformat`` + ``modifier`` combination, and zeroed for the invalid ones.
> +
> +Colospace attributes are not read-only as in the classical version, i.e, they

s/Colospace/Colorspace

> +can be set by application and drivers will adjust accordingly depending on what
> +is supported by the underlying hardware.
> +
> +Buffers
> +=======
> +
> +The API replaces the classical ioctls:
> +
> +:ref:`VIDIOC_CREATE_BUFS <VIDIOC_CREATE_BUFS>`
> +(with :c:type:`v4l2_create_buffers` as the main parameter),
> +:ref:`VIDIOC_QUERYBUF <VIDIOC_QUERYBUF>`, :ref:`VIDIOC_QBUF <VIDIOC_QBUF>`,
> +:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>`, :ref:`VIDIOC_PREPARE_BUF <VIDIOC_PREPARE_BUF>`
> +(with :c:type:`v4l2_buffer` as the main parameter)
> +
> +By the extended versions:
> +
> +:ref:`VIDIOC_EXT_CREATE_BUFS <VIDIOC_EXT_CREATE_BUFS>`
> +(with :c:type:`v4l2_ext_create_buffers` as the main parameter),
> +:ref:`VIDIOC_EXT_QUERYBUF <VIDIOC_EXT_QUERYBUF>`,
> +:ref:`VIDIOC_EXT_QBUF <VIDIOC_EXT_QBUF>`,
> +:ref:`VIDIOC_EXT_DQBUF <VIDIOC_EXT_QBUF>`,
> +:ref:`VIDIOC_EXT_PREPARE_BUF <VIDIOC_EXT_PREPARE_BUF>`
> +(with :c:type:`v4l2_ext_buffer` as the main parameter)
> +
> +The basic difference between :c:type:`v4l2_create_buffers` and
> +:c:type:`v4l2_ext_create_buffers` is that the later have a
> +:c:type:`v4l2_ext_pix_format` as the type of the ``format`` field.
> +
> +Comparing :c:type:`v4l2_ext_buffer` with :c:type:`v4l2_buffer`, in the
> +extended version there is a unification of the single-/multi- planar handling
> +through the ``planes`` field of type :c:type:`v4l2_ext_plane`.
> +
> +The :c:type:`v4l2_ext_plane also allows planes to be placed in a given offset

Missing ` after v4l2_ext_plane.


> +inside a buffer.
> +Planes can be placed in different locations inside the same buffer, or in
> +different buffers.
> +
> +
> +.. kernel-doc:: include/uapi/linux/videodev2.h
> +   :functions: v4l2_ext_plane
> +
> +
> +.. kernel-doc:: include/uapi/linux/videodev2.h
> +   :functions: v4l2_ext_buffer
> diff --git a/Documentation/userspace-api/media/v4l/format.rst b/Documentation/userspace-api/media/v4l/format.rst
> index e47fc0505727c..b96d26f26793c 100644
> --- a/Documentation/userspace-api/media/v4l/format.rst
> +++ b/Documentation/userspace-api/media/v4l/format.rst
> @@ -28,13 +28,19 @@ format and the driver selects and reports the best the hardware can do
>  to satisfy the request. Of course applications can also just query the
>  current selection.
>
> -A single mechanism exists to negotiate all data formats using the
> -aggregate struct :c:type:`v4l2_format` and the
> +There are two mechanism to negociate data formats:
> +
> +The first one is using the aggregate struct :c:type:`v4l2_format` and the
>  :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and
>  :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctls. Additionally the
>  :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl can be used to examine
>  what the hardware *could* do, without actually selecting a new data
> -format. The data formats supported by the V4L2 API are covered in the
> +format.
> +
> +The second is through the :ref:`ext_api`, please refer to its documentation
> +for more information.
> +
> +The data formats supported by the V4L2 API are covered in the
>  respective device section in :ref:`devices`. For a closer look at
>  image formats see :ref:`pixfmt`.
>
> @@ -71,7 +77,9 @@ earlier versions of V4L2. Switching the logical stream or returning into
>  *may* support a switch using :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`.
>
>  All drivers exchanging data with applications must support the
> -:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl. Implementation of the
> +:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl
> +or the Extended respective versions (TODO: link).
> +Implementation of the
>  :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` is highly recommended but optional.
>
>
> diff --git a/Documentation/userspace-api/media/v4l/user-func.rst b/Documentation/userspace-api/media/v4l/user-func.rst
> index bf77c842718e5..67b254812791c 100644
> --- a/Documentation/userspace-api/media/v4l/user-func.rst
> +++ b/Documentation/userspace-api/media/v4l/user-func.rst
> @@ -20,6 +20,7 @@ Function Reference
>      func-close
>      func-ioctl
>      vidioc-create-bufs
> +    vidioc-ext-create-bufs
>      vidioc-cropcap
>      vidioc-dbg-g-chip-info
>      vidioc-dbg-g-register
> @@ -48,6 +49,7 @@ Function Reference
>      vidioc-g-ext-ctrls
>      vidioc-g-fbuf
>      vidioc-g-fmt
> +    vidioc-g-ext-pix-fmt
>      vidioc-g-frequency
>      vidioc-g-input
>      vidioc-g-jpegcomp
> @@ -62,8 +64,11 @@ Function Reference
>      vidioc-log-status
>      vidioc-overlay
>      vidioc-prepare-buf
> +    vidioc-ext-prepare-buf
>      vidioc-qbuf
> +    vidioc-ext-qbuf
>      vidioc-querybuf
> +    vidioc-ext-querybuf
>      vidioc-querycap
>      vidioc-queryctrl
>      vidioc-query-dv-timings
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-ext-create-bufs.rst b/Documentation/userspace-api/media/v4l/vidioc-ext-create-bufs.rst
> new file mode 100644
> index 0000000000000..67f2c541e4d79
> --- /dev/null
> +++ b/Documentation/userspace-api/media/v4l/vidioc-ext-create-bufs.rst
> @@ -0,0 +1,95 @@
> +.. 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/userspace-api/media/fdl-appendix.rst.
> +..
> +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
> +
> +.. _VIDIOC_EXT_CREATE_BUFS:
> +
> +****************************
> +ioctl VIDIOC_EXT_CREATE_BUFS
> +****************************
> +
> +Name
> +====
> +
> +VIDIOC_EXT_CREATE_BUFS - Create buffers for Memory Mapped or User Pointer or DMA Buffer I/O
> +
> +
> +Synopsis
> +========
> +
> +.. c:function:: int ioctl( int fd, VIDIOC_EXT_CREATE_BUFS, struct v4l2_ext_create_buffers *argp )
> +    :name: VIDIOC_EXT_CREATE_BUFS
> +
> +
> +Arguments
> +=========
> +
> +``fd``
> +    File descriptor returned by :ref:`open() <func-open>`.
> +
> +``argp``
> +    Pointer to struct :c:type:`v4l2_ext_create_buffers`.
> +
> +
> +Description
> +===========
> +
> +This ioctl is used to create buffers for :ref:`memory mapped <mmap>`
> +or :ref:`user pointer <userp>` or :ref:`DMA buffer <dmabuf>` I/O.
> +This ioctl can be called multiple times to
> +create buffers of different sizes.
> +
> +To allocate the device buffers applications must initialize the relevant
> +fields of the struct :c:type:`v4l2_ext_create_buffers` structure. The
> +``count`` field must be set to the number of requested buffers, the
> +``memory`` field specifies the requested I/O method and the ``reserved``
> +array must be zeroed.
> +
> +The ``format`` field specifies the image format that the buffers must be
> +able to handle. The application has to fill in this struct
> +:c:type:`v4l2_format`. Usually this will be done using the
> +:ref:`VIDIOC_TRY_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>` or
> +:ref:`VIDIOC_G_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>` ioctls to ensure that the
> +requested format is supported by the driver.
> +The driver may return an error if the size(s) are not supported by the
> +hardware (usually because they are too small).
> +
> +The driver can create a memory buffer per plane, or a single memory buffer
> +containing all the planes, with a minimum size according to the size
> +defined by the ``format.plane_fmt[i].sizeimage`` field.
> +Usually if the ``format.plane_fmt[i].sizeimage``
> +field is less than the minimum required for the given format, then an
> +error will be returned since drivers will typically not allow this. If
> +it is larger, then the value will be used as-is. In other words, the
> +driver may reject the requested size, but if it is accepted the driver
> +will use it unchanged.
> +
> +When the ioctl is called with a pointer to this structure the driver
> +will attempt to allocate up to the requested number of buffers and store
> +the actual number allocated and the starting index in the ``count`` and
> +the ``index`` fields respectively. On return ``count`` can be smaller
> +than the number requested.
> +
> +
> +.. kernel-doc:: include/uapi/linux/videodev2.h
> +   :functions: v4l2_ext_create_buffers
> +
> +
> +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.
> +
> +ENOMEM
> +    No memory to allocate buffers for :ref:`memory mapped <mmap>` I/O.
> +
> +EINVAL
> +    The buffer type (``format.type`` field), requested I/O method
> +    (``memory``) or format (``format`` field) is not valid.
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-ext-prepare-buf.rst b/Documentation/userspace-api/media/v4l/vidioc-ext-prepare-buf.rst
> new file mode 100644
> index 0000000000000..88e4b57121254
> --- /dev/null
> +++ b/Documentation/userspace-api/media/v4l/vidioc-ext-prepare-buf.rst
> @@ -0,0 +1,62 @@
> +.. 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/userspace-api/media/fdl-appendix.rst.
> +..
> +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
> +
> +.. _VIDIOC_EXT_PREPARE_BUF:
> +
> +****************************
> +ioctl VIDIOC_EXT_PREPARE_BUF
> +****************************
> +
> +Name
> +====
> +
> +VIDIOC_EXT_PREPARE_BUF - Prepare a buffer for I/O
> +
> +
> +Synopsis
> +========
> +
> +.. c:function:: int ioctl( int fd, VIDIOC_EXT_PREPARE_BUF, struct v4l2_ext_buffer *argp )
> +    :name: VIDIOC_EXT_PREPARE_BUF
> +
> +
> +Arguments
> +=========
> +
> +``fd``
> +    File descriptor returned by :ref:`open() <func-open>`.
> +
> +``argp``
> +    Pointer to struct :c:type:`v4l2_ext_buffer`.
> +
> +
> +Description
> +===========
> +
> +Applications can optionally call the :ref:`VIDIOC_EXT_PREPARE_BUF` ioctl to
> +pass ownership of the buffer to the driver before actually enqueuing it,
> +using the :ref:`VIDIOC_EXT_QBUF <VIDIOC_EXT_QBUF>` ioctl, and to prepare it for future I/O. Such
> +preparations may include cache invalidation or cleaning. Performing them
> +in advance saves time during the actual I/O.
> +
> +
> +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.
> +
> +EBUSY
> +    File I/O is in progress.
> +
> +EINVAL
> +    The buffer ``type`` is not supported, or the ``index`` is out of
> +    bounds, or no buffers have been allocated yet, or the ``userptr`` or
> +    ``length`` are invalid.
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-ext-qbuf.rst b/Documentation/userspace-api/media/v4l/vidioc-ext-qbuf.rst
> new file mode 100644
> index 0000000000000..083e106cf6bad
> --- /dev/null
> +++ b/Documentation/userspace-api/media/v4l/vidioc-ext-qbuf.rst
> @@ -0,0 +1,204 @@
> +.. 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/userspace-api/media/fdl-appendix.rst.
> +..
> +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
> +
> +.. _VIDIOC_EXT_QBUF:
> +
> +***************************************
> +ioctl VIDIOC_EXT_QBUF, VIDIOC_EXT_DQBUF
> +***************************************
> +
> +Name
> +====
> +
> +VIDIOC_EXT_QBUF - VIDIOC_EXT_DQBUF - Exchange a buffer with the driver
> +
> +
> +Synopsis
> +========
> +
> +.. c:function:: int ioctl( int fd, VIDIOC_EXT_QBUF, struct v4l2_ext_buffer *argp )
> +    :name: VIDIOC_EXT_QBUF
> +
> +.. c:function:: int ioctl( int fd, VIDIOC_EXT_DQBUF, struct v4l2_ext_buffer *argp )
> +    :name: VIDIOC_EXT_DQBUF
> +
> +
> +Arguments
> +=========
> +
> +``fd``
> +    File descriptor returned by :ref:`open() <func-open>`.
> +
> +``argp``
> +    Pointer to struct :c:type:`v4l2_ext_buffer`.
> +
> +
> +Description
> +===========
> +
> +Applications call the ``VIDIOC_EXT_QBUF`` ioctl to enqueue an empty
> +(capturing) or filled (output) buffer in the driver's incoming queue.
> +The semantics depend on the selected I/O method.
> +
> +To enqueue a buffer applications set the ``type`` field of a struct
> +:c:type:`v4l2_ext_buffer` to the same buffer type as was
> +previously used with struct :c:type:`v4l2_ext_pix_format` ``type``.
> +Applications must also set the ``index`` field. Valid index numbers
> +range from zero to the number of buffers allocated with
> +:ref:`VIDIOC_EXT_CREATE_BUFS` (struct
> +:c:type:`v4l2_ext_create_buffers` ``count``) minus
> +one. The contents of the struct :c:type:`v4l2_ext_buffer` returned
> +by a :ref:`VIDIOC_EXT_QUERYBUF` ioctl will do as well.
> +When the buffer is intended for output (``type`` is
> +``V4L2_BUF_TYPE_VIDEO_OUTPUT``) applications must also initialize the
> +``timestamp`` fields and the ``planes[i].plane_length`` for each valid plane,
> +and invalid ones must be set as zero.
> +see :ref:`buffer` for details. Applications must also set ``flags`` to 0. The
> +``reserved`` field must be set to 0.
> +
> +To enqueue a :ref:`memory mapped <mmap>` buffer applications set the
> +``planes[i].memory`` field to ``V4L2_MEMORY_MMAP`` in all the valid planes,
> +and invalid ones must be set as zero.
> +When ``VIDIOC_EXT_QBUF`` is called
> +with a pointer to this structure the driver sets the
> +``V4L2_BUF_FLAG_MAPPED`` and ``V4L2_BUF_FLAG_QUEUED`` flags and clears
> +the ``V4L2_BUF_FLAG_DONE`` flag in the ``flags`` field, or it returns an
> +``EINVAL`` error code.
> +
> +To enqueue a :ref:`user pointer <userp>` buffer applications set the
> +``planes[i].memory`` field to ``V4L2_MEMORY_USERPTR`` in all the valid planes,
> +and invalid ones must be set as zero, the ``planes[i].m.userptr`` field to the
> +address of the buffer,``planes[i].buffer_length`` to the size of the memory

These backquotes appear as-is in the html document for some reason.

> +buffer, ``planes[i].plane_length`` to the size that should be used by the plane,
> +and ``planes[i].offset`` of the plane in the memory buffer.
> +
> +When ``VIDIOC_EXT_QBUF`` is called with a pointer to this structure
> +the driver sets the ``V4L2_BUF_FLAG_QUEUED`` flag and clears the
> +``V4L2_BUF_FLAG_MAPPED`` and ``V4L2_BUF_FLAG_DONE`` flags in the
> +``flags`` field, or it returns an error code. This ioctl locks the
> +memory pages of the buffer in physical memory, they cannot be swapped
> +out to disk. Buffers remain locked until dequeued, until the
> +:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` or
> +:ref:`VIDIOC_EXT_CREATE_BUFS` ioctl is called, or until the

Just for my education, why does VIDIOC_EXT_CREATE_BUFS unlock user buffer pages?

> +device is closed.
> +
> +To enqueue a :ref:`DMABUF <dmabuf>` buffer applications set the
> +``planes[i].memory`` field to ``V4L2_MEMORY_DMABUF`` in all the valid planes,
> +and invalid ones must be set as zero, the ``planes[i].m.fd`` field to a
> +file descriptor associated with a DMABUF buffer.,``planes[i].buffer_length`` to

Same issue with the backquotes appearing as-is in the html - maybe we
need a space before them?


> +the size of the memory buffer, ``planes[i].plane_length`` to the size that
> +should be used by the plane, and ``planes[i].offset`` of the plane in the memory buffer.
> +When ``VIDIOC_EXT_QBUF`` is called with a pointer to this structure the driver
> +sets the ``V4L2_BUF_FLAG_QUEUED`` flag and clears the
> +``V4L2_BUF_FLAG_MAPPED`` and ``V4L2_BUF_FLAG_DONE`` flags in the
> +``flags`` field, or it returns an error code. This ioctl locks the
> +buffer. Locking a buffer means passing it to a driver for a hardware
> +access (usually DMA). If an application accesses (reads/writes) a locked
> +buffer then the result is undefined. Buffers remain locked until
> +dequeued, until the :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` or
> +:ref:`VIDIOC_EXT_CREATE_BUFS` ioctl is called, or until the
> +device is closed.
> +
> +The ``request_fd`` field can be used with the ``VIDIOC_EXT_QBUF`` ioctl to specify
> +the file descriptor of a :ref:`request <media-request-api>`, if requests are
> +in use. Setting it means that the buffer will not be passed to the driver
> +until the request itself is queued. Also, the driver will apply any
> +settings associated with the request for this buffer. This field will
> +be ignored unless the ``V4L2_BUF_FLAG_REQUEST_FD`` flag is set.
> +If the device does not support requests, then ``EBADR`` will be returned.
> +If requests are supported but an invalid request file descriptor is given,
> +then ``EINVAL`` will be returned.
> +
> +.. caution::
> +   It is not allowed to mix queuing requests with queuing buffers directly.
> +   ``EBUSY`` will be returned if the first buffer was queued directly and
> +   then the application tries to queue a request, or vice versa. After
> +   closing the file descriptor, calling
> +   :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` or calling :ref:`VIDIOC_EXT_CREATE_BUFS`
> +   the check for this will be reset.
> +
> +   For :ref:`memory-to-memory devices <mem2mem>` you can specify the
> +   ``request_fd`` only for output buffers, not for capture buffers. Attempting
> +   to specify this for a capture buffer will result in an ``EBADR`` error.
> +
> +Applications call the ``VIDIOC_EXT_DQBUF`` ioctl to dequeue a filled
> +(capturing) or displayed (output) buffer from the driver's outgoing
> +queue. They just set the ``type``, ``planes[i].memory`` and ``reserved`` fields of
> +a struct :c:type:`v4l2_ext_buffer` as above, when
> +``VIDIOC_EXT_DQBUF`` is called with a pointer to this structure the driver
> +fills the remaining fields or returns an error code. The driver may also
> +set ``V4L2_BUF_FLAG_ERROR`` in the ``flags`` field. It indicates a
> +non-critical (recoverable) streaming error. In such case the application
> +may continue as normal, but should be aware that data in the dequeued
> +buffer might be corrupted. When using the multi-planar API, the planes
> +array must be passed in as well.
> +
> +If the application sets the ``memory`` field to ``V4L2_MEMORY_DMABUF`` to
> +dequeue a :ref:`DMABUF <dmabuf>` buffer, the driver fills the ``m.fd`` field
> +with a file descriptor numerically the same as the one given to ``VIDIOC_EXT_QBUF``
> +when the buffer was enqueued. No new file descriptor is created at dequeue time
> +and the value is only for the application convenience.
> +
> +By default ``VIDIOC_EXT_DQBUF`` blocks when no buffer is in the outgoing
> +queue. When the ``O_NONBLOCK`` flag was given to the
> +:ref:`open() <func-open>` function, ``VIDIOC_EXT_DQBUF`` returns
> +immediately with an ``EAGAIN`` error code when no buffer is available.
> +
> +
> +.. kernel-doc:: include/uapi/linux/videodev2.h
> +   :functions: v4l2_ext_buffers
> +
> +
> +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.
> +
> +EAGAIN
> +    Non-blocking I/O has been selected using ``O_NONBLOCK`` and no
> +    buffer was in the outgoing queue.
> +
> +EINVAL
> +    The buffer ``type`` is not supported, or the ``index`` is out of
> +    bounds, or no buffers have been allocated yet, or the ``userptr`` or
> +    ``length`` are invalid, or the ``V4L2_BUF_FLAG_REQUEST_FD`` flag was
> +    set but the the given ``request_fd`` was invalid, or ``m.fd`` was
> +    an invalid DMABUF file descriptor.
> +
> +EIO
> +    ``VIDIOC_EXT_DQBUF`` failed due to an internal error. Can also indicate
> +    temporary problems like signal loss.
> +
> +    .. note::
> +
> +       The driver might dequeue an (empty) buffer despite returning
> +       an error, or even stop capturing. Reusing such buffer may be unsafe
> +       though and its details (e.g. ``index``) may not be returned either.
> +       It is recommended that drivers indicate recoverable errors by setting
> +       the ``V4L2_BUF_FLAG_ERROR`` and returning 0 instead. In that case the
> +       application should be able to safely reuse the buffer and continue
> +       streaming.
> +
> +EPIPE
> +    ``VIDIOC_EXT_DQBUF`` returns this on an empty capture queue for mem2mem
> +    codecs if a buffer with the ``V4L2_BUF_FLAG_LAST`` was already
> +    dequeued and no new buffers are expected to become available.
> +
> +EBADR
> +    The ``V4L2_BUF_FLAG_REQUEST_FD`` flag was set but the device does not
> +    support requests for the given buffer type, or
> +    the ``V4L2_BUF_FLAG_REQUEST_FD`` flag was not set but the device requires
> +    that the buffer is part of a request.
> +
> +EBUSY
> +    The first buffer was queued via a request, but the application now tries
> +    to queue it directly, or vice versa (it is not permitted to mix the two
> +    APIs).
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-ext-querybuf.rst b/Documentation/userspace-api/media/v4l/vidioc-ext-querybuf.rst
> new file mode 100644
> index 0000000000000..f2a12017253f6
> --- /dev/null
> +++ b/Documentation/userspace-api/media/v4l/vidioc-ext-querybuf.rst
> @@ -0,0 +1,79 @@
> +.. 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/userspace-api/media/fdl-appendix.rst.
> +..
> +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
> +
> +.. _VIDIOC_EXT_QUERYBUF:
> +
> +*************************
> +ioctl VIDIOC_EXT_QUERYBUF
> +*************************
> +
> +Name
> +====
> +
> +VIDIOC_EXT_QUERYBUF - Query the status of a buffer
> +
> +
> +Synopsis
> +========
> +
> +.. c:function:: int ioctl( int fd, VIDIOC_EXT_QUERYBUF, struct v4l2_ext_buffer *argp )
> +    :name: VIDIOC_EXT_QUERYBUF
> +
> +
> +Arguments
> +=========
> +
> +``fd``
> +    File descriptor returned by :ref:`open() <func-open>`.
> +
> +``argp``
> +    Pointer to struct :c:type:`v4l2_ext_buffer`.
> +
> +
> +Description
> +===========
> +
> +This ioctl is part of the :ref:`streaming <mmap>` I/O method. It can
> +be used to query the status of a buffer at any time after buffers have
> +been allocated with the :ref:`VIDIOC_EXT_CREATE_BUFS` ioctl.
> +
> +Applications set the ``type`` field of a struct
> +:c:type:`v4l2_ext_buffer` to the same buffer type as was
> +previously used with struct :c:type:`v4l2_ext_pix_format` ``type``,
> +and the ``index`` field. Valid index numbers range from zero to the
> +number of buffers allocated with
> +:ref:`VIDIOC_EXT_CREATE_BUFS` (struct
> +:c:type:`v4l2_ext_create_buffers` ``count``) minus
> +one. The ``reserved`` field must be set to 0.
> +
> +In the ``flags`` field the ``V4L2_BUF_FLAG_MAPPED``,
> +``V4L2_BUF_FLAG_PREPARED``, ``V4L2_BUF_FLAG_QUEUED`` and
> +``V4L2_BUF_FLAG_DONE`` flags will be valid. The ``planes.memory`` fields will be
> +set to the current I/O method for each plane.
> +
> +For every valid plane, an entry in ``planes`` will be filled, and zeroed for
> +invalid ones. ``planes[i].buffer_length`` is the size of the memory buffer
> +which contains the plane, ``planes[i].plane_length`` is the length of the plane,
> +and ``planes[i].offset` is where the plane is placed in the memory buffer.
> +
> +The size of the ``planes`` array can be calculated by the number of sequential
> +planes with ``planes[i].buffer_length`` that differs from zero up to the max
> +size of the array.
> +
> +
> +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.
> +
> +EINVAL
> +    The buffer ``type`` is not supported, or the ``index`` is out of
> +    bounds.
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-ext-pix-fmt.rst b/Documentation/userspace-api/media/v4l/vidioc-g-ext-pix-fmt.rst
> new file mode 100644
> index 0000000000000..008e6c98a88a5
> --- /dev/null
> +++ b/Documentation/userspace-api/media/v4l/vidioc-g-ext-pix-fmt.rst
> @@ -0,0 +1,117 @@
> +.. 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/userspace-api/media/fdl-appendix.rst.
> +..
> +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
> +
> +.. _VIDIOC_G_EXT_PIX_FMT:
> +
> +************************************************************************
> +ioctl VIDIOC_G_EXT_PIX_FMT, VIDIOC_S_EXT_PIX_FMT, VIDIOC_TRY_EXT_PIX_FMT
> +************************************************************************
> +
> +Name
> +====
> +
> +VIDIOC_G_EXT_PIX_FMT - VIDIOC_S_EXT_PIX_FMT - VIDIOC_TRY_EXT_PIX_FMT - Get or set the data format, try a format
> +
> +
> +Synopsis
> +========
> +
> +.. c:function:: int ioctl( int fd, VIDIOC_G_EXT_PIX_FMT, struct v4l2_ext_pix_format *argp )
> +    :name: VIDIOC_G_EXT_PIX_FMT
> +
> +.. c:function:: int ioctl( int fd, VIDIOC_S_EXT_PIX_FMT, struct v4l2_ext_pix_format *argp )
> +    :name: VIDIOC_S_EXT_PIX_FMT
> +
> +.. c:function:: int ioctl( int fd, VIDIOC_TRY_EXT_PIX_FMT, struct v4l2_ext_pix_format *argp )
> +    :name: VIDIOC_TRY_EXT_PIX_FMT
> +
> +Arguments
> +=========
> +
> +``fd``
> +    File descriptor returned by :ref:`open() <func-open>`.
> +
> +``argp``
> +    Pointer to struct :c:type:`v4l2_ext_pix_format`.
> +
> +
> +Description
> +===========
> +
> +These ioctls are used to negotiate the format of data (typically image
> +format) exchanged between driver and application.
> +
> +To query the current parameters applications set the ``type`` field of a
> +struct :c:type:`v4l2_ext_pix_format` to  ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or
> +``V4L2_BUF_TYPE_VIDEO_OUTPUT``, all the other types are invalid in this API,
> +and multiplanar is supported through modifiers.
> +
> +When the application calls the
> +:ref:`VIDIOC_G_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>` ioctl with a pointer to this
> +structure the driver fills the other members.
> +When the requested buffer type is not supported drivers return
> +an ``EINVAL`` error code.
> +
> +To change the current format parameters applications initialize all
> +the fields in the struct.
> +For details see the documentation of the various devices types in
> +:ref:`devices`. Good practice is to query the current parameters
> +first, and to modify only those parameters not suitable for the
> +application. When the application calls the :ref:`VIDIOC_S_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>` ioctl with
> +a pointer to a struct :c:type:`v4l2_ext_pix_format` structure the driver
> +checks and adjusts the parameters against hardware abilities. Drivers
> +should not return an error code unless the ``type`` field is invalid,
> +this is a mechanism to fathom device capabilities and to approach
> +parameters acceptable for both the application and driver. On success
> +the driver may program the hardware, allocate resources and generally
> +prepare for data exchange. Finally the :ref:`VIDIOC_S_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>` ioctl returns
> +the current format parameters as :ref:`VIDIOC_G_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>` does. Very simple,
> +inflexible devices may even ignore all input and always return the
> +default parameters. However all V4L2 devices exchanging data with the
> +application must implement the :ref:`VIDIOC_G_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>` and :ref:`VIDIOC_S_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>`
> +ioctl. When the requested buffer type is not supported drivers return an
> +EINVAL error code on a :ref:`VIDIOC_S_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>` attempt. When I/O is already in
> +progress or the resource is not available for other reasons drivers
> +return the ``EBUSY`` error code.
> +
> +The :ref:`VIDIOC_TRY_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>` ioctl is equivalent to :ref:`VIDIOC_S_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>` with one
> +exception: it does not change driver state. It can also be called at any
> +time, never returning ``EBUSY``. This function is provided to negotiate
> +parameters, to learn about hardware limitations, without disabling I/O
> +or possibly time consuming hardware preparations. Although strongly
> +recommended drivers are not required to implement this ioctl.
> +
> +The format as returned by :ref:`VIDIOC_TRY_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>` must be identical to what
> +:ref:`VIDIOC_S_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>` returns for the same input or output.
> +
> +
> +.. kernel-doc:: include/uapi/linux/videodev2.h
> +   :functions: v4l2_plane_ext_pix_format
> +
> +
> +.. kernel-doc:: include/uapi/linux/videodev2.h
> +   :functions: v4l2_ext_pix_format
> +
> +
> +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.
> +
> +EINVAL
> +    The struct :c:type:`v4l2_ext_pix_format` ``type`` field is
> +    invalid or the requested buffer type not supported.
> +
> +EBUSY
> +    The device is busy and cannot change the format. This could be
> +    because or the device is streaming or buffers are allocated or
> +    queued to the driver. Relevant for :ref:`VIDIOC_S_EXT_PIX_FMT
> +    <VIDIOC_G_EXT_PIX_FMT>` only.
> --
> 2.28.0.rc2
>