On Wed, Feb 21, 2024 at 12:30 PM Tomasz Figa tfiga@chromium.org wrote:
On Sat, Feb 17, 2024 at 6:42 PM Mauro Carvalho Chehab mchehab@kernel.org wrote:
Em Thu, 18 Jan 2024 20:32:00 +0800 Shengjiu Wang shengjiu.wang@nxp.com escreveu:
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@nxp.com
.../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-compat-ioctl32.c | 9 +++ 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 +++++ 13 files changed, 222 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 52bbee81c080..a3754ca6f0d6 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``
- 16Hmm... alsa APi define input/output as: enum { SNDRV_PCM_STREAM_PLAYBACK = 0, SNDRV_PCM_STREAM_CAPTURE, SNDRV_PCM_STREAM_LAST = SNDRV_PCM_STREAM_CAPTURE, };
I would use a namespace as close as possible to the ALSA API. Also, we're not talking about V4L2, but, instead audio. so, not sure if I like the prefix to start with V4L2_. Maybe ALSA_?
So, a better namespace would be:
${prefix}_BUF_TYPE_PCM_STREAM_PLAYBACKand ${prefix}_BUF_TYPE_PCM_STREAM_CAPTURE
The API is still V4L2, and all the other non-video buf types also use the V4L2_ prefix, so perhaps that's good here as well?
Whether AUDIO or PCM_STREAM makes more sense goes outside of my expertise. Subjectively, a PCM stream sounds more specific than an audio stream. Do those buf types also support non-PCM audio streams?
Currently I use it for PCM, but I think it can also be used for non-PCM. So use the below name? V4L2_BUF_TYPE_AUDIO_CAPTURE V4L2_BUF_TYPE_AUDIO_PLAYBACK
- 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..68faecfe3a02 --- /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 +********************************
+An audio memory-to-memory device can compress, decompress, transform, or +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 audio codecs, audio preprocessing, +audio postprocessing.
+A memory-to-memory audio node supports both output (sending audio frames from +memory to the hardware) and capture (receiving the processed 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`pixelformat doesn't make any sense for audio: there are no pixels on a PCM stream. Please use call it, instead: `snd_pcm_format`, making it match the values for snd_pcm_format_t.
+1
FWIW v4l2_meta_format uses the name "dataformat".
Actually, I just realized that the C code actually uses the name "audioformat". Tbh., after reading the kerneldoc comment, my subjective preference would be on "sample_format", since that's exactly what it is.
Ok, I will change it to sampleformat.
Best Regards Shengjiu Wang
Yet, I would keep defining it as u32 (or u64?) instead of using a typedef int field there (snd_pcm_format_t), as the size of integer is different on 32 and 64 bit kernels.
+1
Best regards, Tomasz