[RFC PATCH v6 11/11] media: docs: add documentation for the Extended API
From: Helen Koike
Date: Thu Jan 14 2021 - 13:09:46 EST
Add documentation and update references in current documentation for the
Extended API.
Signed-off-by: Helen Koike <helen.koike@xxxxxxxxxxxxx>
---
Changes in v6:
- Update note saying ext_api should be used for new applications on
newer kernels (Tomasz and Hans)
- Fix typos pointed in v5 (Hand and Tomasz)
- Change order, mention Ext first in format.rst (Tomasz)
- Mention planes[i].offset should be set to zero for userptr
- Remove ext_create_buf and ext_prep_buf from the docs
- s/displayed/consumed for output (Tomasz)
- Remove references for plane length
- Drop EIO sentence mentioning signal loss (Hans)
- Removed first half of the note in EIO (Tomas and Hans)
- Update text to mention EXT_TRY_FMT is mandatory (Hans and Tomasz)
- Remove requirement to fill `memory` field for dqbuf (Tomasz)
- EXT_DQBUF sets `m` field to zero (Tomasz for DMA-fd)
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 | 6 +
.../userspace-api/media/v4l/dev-output.rst | 6 +
.../userspace-api/media/v4l/ext-api.rst | 89 +++++++++
.../userspace-api/media/v4l/format.rst | 18 +-
.../userspace-api/media/v4l/user-func.rst | 5 +
.../media/v4l/vidioc-ext-qbuf.rst | 188 ++++++++++++++++++
.../media/v4l/vidioc-g-ext-pix-fmt.rst | 116 +++++++++++
.../userspace-api/media/v4l/vidioc-qbuf.rst | 2 +-
10 files changed, 431 insertions(+), 5 deletions(-)
create mode 100644 Documentation/userspace-api/media/v4l/ext-api.rst
create mode 100644 Documentation/userspace-api/media/v4l/vidioc-ext-qbuf.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 1b0fdc160533..89652fa7a098 100644
--- a/Documentation/userspace-api/media/v4l/buffer.rst
+++ b/Documentation/userspace-api/media/v4l/buffer.rst
@@ -21,6 +21,11 @@ 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::
+
+ For modern applications on newer kernels, these operations are replaced
+ by their :ref:`ext_api` counterparts, which should be used instead.
+
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 8c263c5a85d8..61a64065f9f3 100644
--- a/Documentation/userspace-api/media/v4l/common.rst
+++ b/Documentation/userspace-api/media/v4l/common.rst
@@ -53,6 +53,7 @@ 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 fe58fd450e2f..73580e16057c 100644
--- a/Documentation/userspace-api/media/v4l/dev-capture.rst
+++ b/Documentation/userspace-api/media/v4l/dev-capture.rst
@@ -93,6 +93,12 @@ 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::
+
+ For modern applications on newer kernels, these operations are replaced
+ by their :ref:`ext_api` counterparts, which should be used instead.
+
+
Reading Images
==============
diff --git a/Documentation/userspace-api/media/v4l/dev-output.rst b/Documentation/userspace-api/media/v4l/dev-output.rst
index eadcb4aa813b..676578c099b6 100644
--- a/Documentation/userspace-api/media/v4l/dev-output.rst
+++ b/Documentation/userspace-api/media/v4l/dev-output.rst
@@ -90,6 +90,12 @@ 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::
+
+ For modern applications on newer kernels, these operations are replaced
+ by their :ref:`ext_api` counterparts, which should be used instead.
+
+
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 000000000000..e73d5b77a550
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/ext-api.rst
@@ -0,0 +1,89 @@
+.. 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:
+
+*************
+Extended API
+*************
+
+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 mention only 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``.
+
+The ``plane_fmt`` field is an array which holds information by plane using
+the :c:type:`v4l2_plane_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.
+
+Colorspace attributes are not read-only as in the classical version, i.e, they
+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_QBUF <VIDIOC_QBUF>`,
+:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>`,
+(with :c:type:`v4l2_buffer` as the main parameter)
+
+By the extended versions:
+
+:ref:`VIDIOC_EXT_QBUF <VIDIOC_EXT_QBUF>`,
+:ref:`VIDIOC_EXT_DQBUF <VIDIOC_EXT_QBUF>`,
+(with :c:type:`v4l2_ext_buffer` as the main parameter)
+
+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
+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 35bbb2fea46e..713e1a9f699a 100644
--- a/Documentation/userspace-api/media/v4l/format.rst
+++ b/Documentation/userspace-api/media/v4l/format.rst
@@ -21,13 +21,19 @@ 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 negotiate data formats:
+
+The first one is through the :ref:`ext_api`, please refer to its documentation
+for more information.
+
+The second 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 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`.
@@ -64,8 +70,12 @@ 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 ref:`Extended <VIDIOC_G_EXT_PIX_FMT>` respective versions.
+Implementation of the
:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` is highly recommended but optional.
+For the Extended API, ref:`VIDIOC_TRY_EXT_PIX_FMT <VIDIOC_G_EXT_PIX_FMT>` is
+mandatory.
Image Format Enumeration
========================
diff --git a/Documentation/userspace-api/media/v4l/user-func.rst b/Documentation/userspace-api/media/v4l/user-func.rst
index 53e604bd7d60..3e21a780033d 100644
--- a/Documentation/userspace-api/media/v4l/user-func.rst
+++ b/Documentation/userspace-api/media/v4l/user-func.rst
@@ -13,6 +13,7 @@ Function Reference
func-close
func-ioctl
vidioc-create-bufs
+ vidioc-ext-create-bufs
vidioc-cropcap
vidioc-dbg-g-chip-info
vidioc-dbg-g-register
@@ -41,6 +42,7 @@ 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
@@ -55,8 +57,11 @@ 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-qbuf.rst b/Documentation/userspace-api/media/v4l/vidioc-ext-qbuf.rst
new file mode 100644
index 000000000000..d137eddc331e
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/vidioc-ext-qbuf.rst
@@ -0,0 +1,188 @@
+.. 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_REQBUFS` (struct
+:c:type:`v4l2_requestbuffers` ``count``) minus
+one.
+When the buffer is intended for output (``type`` is
+``V4L2_BUF_TYPE_VIDEO_OUTPUT``) applications must also initialize the
+``timestamp`` fields.
+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
+``memory`` field to ``V4L2_MEMORY_MMAP``.
+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
+``memory`` field to ``V4L2_MEMORY_USERPTR``, the ``planes[i].m.userptr``
+field to the address of the buffer and ``planes[i].offset`` should be zero.
+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_REQBUFS` ioctl is called, or until the
+device is closed.
+
+To enqueue a :ref:`DMABUF <dmabuf>` buffer applications set the
+``memory`` field to ``V4L2_MEMORY_DMABUF``, the ``planes[i].m.fd`` field to a
+file descriptor associated with a DMABUF buffer
+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_REQBUFS` 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_REQBUFS`
+ 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`` 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.
+
+Pointers in ``m`` field is set to zero. Applications must track the buffers
+in queuing time.
+
+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``
+ 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.
+
+ .. note::
+
+ 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-g-ext-pix-fmt.rst b/Documentation/userspace-api/media/v4l/vidioc-g-ext-pix-fmt.rst
new file mode 100644
index 000000000000..6cb14390dc51
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/vidioc-g-ext-pix-fmt.rst
@@ -0,0 +1,116 @@
+.. 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.
+
+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_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.
diff --git a/Documentation/userspace-api/media/v4l/vidioc-qbuf.rst b/Documentation/userspace-api/media/v4l/vidioc-qbuf.rst
index 77e0747a6d28..7f2aae992348 100644
--- a/Documentation/userspace-api/media/v4l/vidioc-qbuf.rst
+++ b/Documentation/userspace-api/media/v4l/vidioc-qbuf.rst
@@ -121,7 +121,7 @@ then ``EINVAL`` will be returned.
to specify this for a capture buffer will result in an ``EBADR`` error.
Applications call the ``VIDIOC_DQBUF`` ioctl to dequeue a filled
-(capturing) or displayed (output) buffer from the driver's outgoing
+(capturing) or consumed (output) buffer from the driver's outgoing
queue. They just set the ``type``, ``memory`` and ``reserved`` fields of
a struct :c:type:`v4l2_buffer` as above, when
``VIDIOC_DQBUF`` is called with a pointer to this structure the driver
--
2.29.2