linux-kernel - Re: [PATCH v12 08/15] media: uapi: Define audio sample format fourcc type

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Date: Mon, 19 Feb 2024 12:05:02 +0800
From: Shengjiu Wang <shengjiu.wang@...il.com>
To: Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: Shengjiu Wang <shengjiu.wang@....com>, hverkuil@...all.nl, sakari.ailus@....fi, 
	tfiga@...omium.org, m.szyprowski@...sung.com, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Xiubo.Lee@...il.com, festevam@...il.com, 
	nicoleotsuka@...il.com, lgirdwood@...il.com, broonie@...nel.org, 
	perex@...ex.cz, tiwai@...e.com, alsa-devel@...a-project.org, 
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v12 08/15] media: uapi: Define audio sample format fourcc type

Hi Mauro

On Sat, Feb 17, 2024 at 5:19 PM Mauro Carvalho Chehab
<mchehab@...nel.org> wrote:
>
> Em Thu, 18 Jan 2024 20:32:01 +0800
> Shengjiu Wang <shengjiu.wang@....com> escreveu:
>
> > The audio sample format definition is from alsa,
> > the header file is include/uapi/sound/asound.h, but
> > don't include this header file directly, because in
> > user space, there is another copy in alsa-lib.
> > There will be conflict in userspace for include
> > videodev2.h & asound.h and asoundlib.h
> >
> > Here still use the fourcc format.
> >
> > Signed-off-by: Shengjiu Wang <shengjiu.wang@....com>
> > ---
> >  .../userspace-api/media/v4l/pixfmt-audio.rst  | 87 +++++++++++++++++++
> >  .../userspace-api/media/v4l/pixfmt.rst        |  1 +
> >  drivers/media/v4l2-core/v4l2-ioctl.c          | 13 +++
> >  include/uapi/linux/videodev2.h                | 23 +++++
> >  4 files changed, 124 insertions(+)
> >  create mode 100644 Documentation/userspace-api/media/v4l/pixfmt-audio.rst
> >
> > diff --git a/Documentation/userspace-api/media/v4l/pixfmt-audio.rst b/Documentation/userspace-api/media/v4l/pixfmt-audio.rst
> > new file mode 100644
> > index 000000000000..04b4a7fbd8f4
> > --- /dev/null
> > +++ b/Documentation/userspace-api/media/v4l/pixfmt-audio.rst
> > @@ -0,0 +1,87 @@
> > +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
> > +
> > +.. _pixfmt-audio:
> > +
> > +*************
> > +Audio Formats
> > +*************
> > +
> > +These formats are used for :ref:`audiomem2mem` interface only.
> > +
> > +.. tabularcolumns:: |p{5.8cm}|p{1.2cm}|p{10.3cm}|
> > +
> > +.. cssclass:: longtable
> > +
> > +.. flat-table:: Audio Format
> > +    :header-rows:  1
> > +    :stub-columns: 0
> > +    :widths:       3 1 4
> > +
> > +    * - Identifier
> > +      - Code
> > +      - Details
> > +    * .. _V4L2-AUDIO-FMT-S8:
> > +
> > +      - ``V4L2_AUDIO_FMT_S8``
> > +      - 'S8'
> > +      - Corresponds to SNDRV_PCM_FORMAT_S8 in ALSA
> > +    * .. _V4L2-AUDIO-FMT-S16-LE:
>
> Hmm... why can't we just use SNDRV_*_FORMAT_*? Those are already part of
> an uAPI header. No need to add any abstraction here and/or redefine
> what is there already at include/uapi/sound/asound.h.
>
Actually I try to avoid including the include/uapi/sound/asound.h.
Because in user space, there is another copy in alsa-lib (asoundlib.h).
There will be conflict in userspace when including videodev2.h and
asoundlib.h.

And in the V4l framework, the fourcc type is commonly used in other
cases (video, radio, touch, meta....), to avoid changing common code
a lot, so I think using fourcc definition for audio may be simpler.

Best regards
Shengjiu Wang