On 13/10/2023 10:31, Shengjiu Wang wrote:
> Audio signal processing has the requirement for memory to
> memory similar as Video.
>
> This patch is to add this support in v4l2 framework, defined
> new buffer type V4L2_BUF_TYPE_AUDIO_CAPTURE and
> V4L2_BUF_TYPE_AUDIO_OUTPUT, defined new format v4l2_audio_format
> for audio case usage.
>
> The created audio device is named "/dev/v4l-audioX".
>
> Signed-off-by: Shengjiu Wang <shengjiu.wang@xxxxxxx>
> ---
> .../userspace-api/media/v4l/buffer.rst | 6 ++
> .../media/v4l/dev-audio-mem2mem.rst | 71 +++++++++++++++++++
> .../userspace-api/media/v4l/devices.rst | 1 +
> .../media/v4l/vidioc-enum-fmt.rst | 2 +
> .../userspace-api/media/v4l/vidioc-g-fmt.rst | 4 ++
> .../media/videodev2.h.rst.exceptions | 2 +
> .../media/common/videobuf2/videobuf2-v4l2.c | 4 ++
> drivers/media/v4l2-core/v4l2-dev.c | 17 +++++
> drivers/media/v4l2-core/v4l2-ioctl.c | 53 ++++++++++++++
> include/media/v4l2-dev.h | 2 +
> include/media/v4l2-ioctl.h | 34 +++++++++
> include/uapi/linux/videodev2.h | 17 +++++
> 12 files changed, 213 insertions(+)
> create mode 100644 Documentation/userspace-api/media/v4l/dev-audio-mem2mem.rst
>
> diff --git a/Documentation/userspace-api/media/v4l/buffer.rst b/Documentation/userspace-api/media/v4l/buffer.rst
> index 04dec3e570ed..80cf2cb20dfe 100644
> --- a/Documentation/userspace-api/media/v4l/buffer.rst
> +++ b/Documentation/userspace-api/media/v4l/buffer.rst
> @@ -438,6 +438,12 @@ enum v4l2_buf_type
> * - ``V4L2_BUF_TYPE_META_OUTPUT``
> - 14
> - Buffer for metadata output, see :ref:`metadata`.
> + * - ``V4L2_BUF_TYPE_AUDIO_CAPTURE``
> + - 15
> + - Buffer for audio capture, see :ref:`audio`.
> + * - ``V4L2_BUF_TYPE_AUDIO_OUTPUT``
> + - 16
> + - Buffer for audio output, see :ref:`audio`.
>
>
> .. _buffer-flags:
> diff --git a/Documentation/userspace-api/media/v4l/dev-audio-mem2mem.rst b/Documentation/userspace-api/media/v4l/dev-audio-mem2mem.rst
> new file mode 100644
> index 000000000000..2ea493d0a73b
> --- /dev/null
> +++ b/Documentation/userspace-api/media/v4l/dev-audio-mem2mem.rst
> @@ -0,0 +1,71 @@
> +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
> +
> +.. _audiomem2mem:
> +
> +********************************
> +Audio Memory-To-Memory Interface
> +********************************
> +
> +A audio memory-to-memory device can compress, decompress, transform, or
A -> An
> +otherwise convert audio data from one format into another format, in memory.
> +Such memory-to-memory devices set the ``V4L2_CAP_AUDIO_M2M`` capability.
> +Examples of memory-to-memory devices are codecs, audio preprocessing,
codecs -> audio codecs
Reason: within V4L2 'codec' refers to a video codec by default, so for audio
codecs it is better to be explicit and mention 'audio'.
> +audio postprocessing.
> +
> +A memory-to-memory audio node supports both output (sending frames from
I think it is better to write 'audio frames' instead of just 'frames', for
the same reason as why I prefer 'audio codec'. It makes it explicit that we
are dealing with audio.
> +memory to the hardware) and capture (receiving the processed frames
audio frames
> +from the hardware into memory) stream I/O. An application will have to
> +setup the stream I/O for both sides and finally call
> +:ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` for both capture and output to
> +start the hardware.
> +
> +Memory-to-memory devices function as a shared resource: you can
> +open the audio node multiple times, each application setting up their
> +own properties that are local to the file handle, and each can use
> +it independently from the others. The driver will arbitrate access to
> +the hardware and reprogram it whenever another file handler gets access.
> +
> +Audio memory-to-memory devices are accessed through character device
> +special files named ``/dev/v4l-audio``
> +
> +Querying Capabilities
> +=====================
> +
> +Device nodes supporting the audio memory-to-memory interface set the
> +``V4L2_CAP_AUDIO_M2M`` flag in the ``device_caps`` field of the
> +:c:type:`v4l2_capability` structure returned by the :c:func:`VIDIOC_QUERYCAP`
> +ioctl.
> +
> +Data Format Negotiation
> +=======================
> +
> +The audio device uses the :ref:`format` ioctls to select the capture format.
> +The audio buffer content format is bound to that selected format. In addition
> +to the basic :ref:`format` ioctls, the :c:func:`VIDIOC_ENUM_FMT` ioctl must be
> +supported as well.
> +
> +To use the :ref:`format` ioctls applications set the ``type`` field of the
> +:c:type:`v4l2_format` structure to ``V4L2_BUF_TYPE_AUDIO_CAPTURE`` or to
> +``V4L2_BUF_TYPE_AUDIO_OUTPUT``. Both drivers and applications must set the
> +remainder of the :c:type:`v4l2_format` structure to 0.
> +
> +.. c:type:: v4l2_audio_format
> +
> +.. tabularcolumns:: |p{1.4cm}|p{2.4cm}|p{13.5cm}|
> +
> +.. flat-table:: struct v4l2_audio_format
> + :header-rows: 0
> + :stub-columns: 0
> + :widths: 1 1 2
> +
> + * - __u32
> + - ``pixelformat``
> + - The sample format, set by the application. see :ref:`pixfmt-audio`
> + * - __u32
> + - ``channels``
> + - The channel number, set by the application. channel number range is
> + [1, 32].
> + * - __u32
> + - ``buffersize``
> + - Maximum buffer size in bytes required for data. The value is set by the
> + driver.
<snip>
Regards,
Hans
