Re: [PATCH v13 09/16] media: uapi: Define audio sample format fourcc type

[Shengjiu Wang <shengjiu.wang@gmail.com>]

On Mon, Feb 26, 2024 at 9:55 PM Nicolas Dufresne <nicolas@ndufresne.ca> wrote:
>
> Le lundi 26 février 2024 à 16:28 +0800, Shengjiu Wang a écrit :
> > 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.
>
> I'd like to join Mauro's voice that duplicating the audio formats is a bad idea.
> We have the same issues with video formats when you look at V4L2 vs DRM. You're
> rationale is that videodev2.h will be ambiguous if it includes asound.h, but
> looking at this change, there is no reason why you need to include asound.h in
> videodev2.h at all. The format type can be abstracted out with a uint32 in the
> API, and then it would be up to the users to include and use the appropriate
> formats IDs.
>

Resend for the plain text issue

Thanks.

There is another reason mentioned by Hans:

"
The problem is that within V4L2 we use fourcc consistently to describe a
format, including in VIDIOC_ENUM_FMT. And the expectation is that the fourcc
can be printed to a human readable string (there is even a printk format for
that these days).

But the pcm values are all small integers (and can even be 0!), and
printing the fourcc will give garbage. It doesn't work well at all
with the V4L2 API. But by having a straightforward conversion between the
pcm identifier and a fourcc it was really easy to deal with this.

There might even be applications today that call VIDIOC_ENUM_FMT to see
what is supported and fail if it is not a proper fourcc is returned.

It will certainly report nonsense in v4l_print_fmtdesc() (v4l2-ioctl.c).

One of the early versions of this patch series did precisely what you request,
but it just doesn't work well within the V4L2 uAPI.
"

Best regards
Shengjiu Wang
> Nicolas
>
> >
> > Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.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:
> > +
> > +      - ``V4L2_AUDIO_FMT_S16_LE``
> > +      - 'S16_LE'
> > +      - Corresponds to SNDRV_PCM_FORMAT_S16_LE in ALSA
> > +    * .. _V4L2-AUDIO-FMT-U16-LE:
> > +
> > +      - ``V4L2_AUDIO_FMT_U16_LE``
> > +      - 'U16_LE'
> > +      - Corresponds to SNDRV_PCM_FORMAT_U16_LE in ALSA
> > +    * .. _V4L2-AUDIO-FMT-S24-LE:
> > +
> > +      - ``V4L2_AUDIO_FMT_S24_LE``
> > +      - 'S24_LE'
> > +      - Corresponds to SNDRV_PCM_FORMAT_S24_LE in ALSA
> > +    * .. _V4L2-AUDIO-FMT-U24-LE:
> > +
> > +      - ``V4L2_AUDIO_FMT_U24_LE``
> > +      - 'U24_LE'
> > +      - Corresponds to SNDRV_PCM_FORMAT_U24_LE in ALSA
> > +    * .. _V4L2-AUDIO-FMT-S32-LE:
> > +
> > +      - ``V4L2_AUDIO_FMT_S32_LE``
> > +      - 'S32_LE'
> > +      - Corresponds to SNDRV_PCM_FORMAT_S32_LE in ALSA
> > +    * .. _V4L2-AUDIO-FMT-U32-LE:
> > +
> > +      - ``V4L2_AUDIO_FMT_U32_LE``
> > +      - 'U32_LE'
> > +      - Corresponds to SNDRV_PCM_FORMAT_U32_LE in ALSA
> > +    * .. _V4L2-AUDIO-FMT-FLOAT-LE:
> > +
> > +      - ``V4L2_AUDIO_FMT_FLOAT_LE``
> > +      - 'FLOAT_LE'
> > +      - Corresponds to SNDRV_PCM_FORMAT_FLOAT_LE in ALSA
> > +    * .. _V4L2-AUDIO-FMT-IEC958-SUBFRAME-LE:
> > +
> > +      - ``V4L2_AUDIO_FMT_IEC958_SUBFRAME_LE``
> > +      - 'IEC958_SUBFRAME_LE'
> > +      - Corresponds to SNDRV_PCM_FORMAT_IEC958_SUBFRAME_LE in ALSA
> > +    * .. _V4L2-AUDIO-FMT-S24-3LE:
> > +
> > +      - ``V4L2_AUDIO_FMT_S24_3LE``
> > +      - 'S24_3LE'
> > +      - Corresponds to SNDRV_PCM_FORMAT_S24_3LE in ALSA
> > +    * .. _V4L2-AUDIO-FMT-U24-3LE:
> > +
> > +      - ``V4L2_AUDIO_FMT_U24_3LE``
> > +      - 'U24_3LE'
> > +      - Corresponds to SNDRV_PCM_FORMAT_U24_3LE in ALSA
> > +    * .. _V4L2-AUDIO-FMT-S20-3LE:
> > +
> > +      - ``V4L2_AUDIO_FMT_S20_3LE``
> > +      - 'S20_3LE'
> > +      - Corresponds to SNDRV_PCM_FORMAT_S24_3LE in ALSA
> > +    * .. _V4L2-AUDIO-FMT-U20-3LE:
> > +
> > +      - ``V4L2_AUDIO_FMT_U20_3LE``
> > +      - 'U20_3LE'
> > +      - Corresponds to SNDRV_PCM_FORMAT_U20_3LE in ALSA
> > diff --git a/Documentation/userspace-api/media/v4l/pixfmt.rst b/Documentation/userspace-api/media/v4l/pixfmt.rst
> > index 11dab4a90630..2eb6fdd3b43d 100644
> > --- a/Documentation/userspace-api/media/v4l/pixfmt.rst
> > +++ b/Documentation/userspace-api/media/v4l/pixfmt.rst
> > @@ -36,3 +36,4 @@ see also :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>`.)
> >      colorspaces
> >      colorspaces-defs
> >      colorspaces-details
> > +    pixfmt-audio
> > diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> > index 961abcdf7290..be229c69e991 100644
> > --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> > +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> > @@ -1471,6 +1471,19 @@ static void v4l_fill_fmtdesc(struct v4l2_fmtdesc *fmt)
> >       case V4L2_PIX_FMT_Y210:         descr = "10-bit YUYV Packed"; break;
> >       case V4L2_PIX_FMT_Y212:         descr = "12-bit YUYV Packed"; break;
> >       case V4L2_PIX_FMT_Y216:         descr = "16-bit YUYV Packed"; break;
> > +     case V4L2_AUDIO_FMT_S8:         descr = "8-bit Signed"; break;
> > +     case V4L2_AUDIO_FMT_S16_LE:     descr = "16-bit Signed LE"; break;
> > +     case V4L2_AUDIO_FMT_U16_LE:             descr = "16-bit Unsigned LE"; break;
> > +     case V4L2_AUDIO_FMT_S24_LE:             descr = "24(32)-bit Signed LE"; break;
> > +     case V4L2_AUDIO_FMT_U24_LE:             descr = "24(32)-bit Unsigned LE"; break;
> > +     case V4L2_AUDIO_FMT_S32_LE:             descr = "32-bit Signed LE"; break;
> > +     case V4L2_AUDIO_FMT_U32_LE:             descr = "32-bit Unsigned LE"; break;
> > +     case V4L2_AUDIO_FMT_FLOAT_LE:           descr = "32-bit Float LE"; break;
> > +     case V4L2_AUDIO_FMT_IEC958_SUBFRAME_LE: descr = "32-bit IEC958 LE"; break;
> > +     case V4L2_AUDIO_FMT_S24_3LE:            descr = "24(24)-bit Signed LE"; break;
> > +     case V4L2_AUDIO_FMT_U24_3LE:            descr = "24(24)-bit Unsigned LE"; break;
> > +     case V4L2_AUDIO_FMT_S20_3LE:            descr = "20(24)-bit Signed LE"; break;
> > +     case V4L2_AUDIO_FMT_U20_3LE:            descr = "20(24)-bit Unsigned LE"; break;
> >
> >       default:
> >               /* Compressed formats */
> > diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> > index 2c03d2dfadbe..673a6235a029 100644
> > --- a/include/uapi/linux/videodev2.h
> > +++ b/include/uapi/linux/videodev2.h
> > @@ -843,6 +843,29 @@ struct v4l2_pix_format {
> >  #define V4L2_META_FMT_RK_ISP1_PARAMS v4l2_fourcc('R', 'K', '1', 'P') /* Rockchip ISP1 3A Parameters */
> >  #define V4L2_META_FMT_RK_ISP1_STAT_3A        v4l2_fourcc('R', 'K', '1', 'S') /* Rockchip ISP1 3A Statistics */
> >
> > +/*
> > + * Audio-data formats
> > + * All these audio formats use a fourcc starting with 'AU'
> > + * followed by the SNDRV_PCM_FORMAT_ value from asound.h.
> > + */
> > +#define V4L2_AUDIO_FMT_S8                    v4l2_fourcc('A', 'U', '0', '0')
> > +#define V4L2_AUDIO_FMT_S16_LE                        v4l2_fourcc('A', 'U', '0', '2')
> > +#define V4L2_AUDIO_FMT_U16_LE                        v4l2_fourcc('A', 'U', '0', '4')
> > +#define V4L2_AUDIO_FMT_S24_LE                        v4l2_fourcc('A', 'U', '0', '6')
> > +#define V4L2_AUDIO_FMT_U24_LE                        v4l2_fourcc('A', 'U', '0', '8')
> > +#define V4L2_AUDIO_FMT_S32_LE                        v4l2_fourcc('A', 'U', '1', '0')
> > +#define V4L2_AUDIO_FMT_U32_LE                        v4l2_fourcc('A', 'U', '1', '2')
> > +#define V4L2_AUDIO_FMT_FLOAT_LE                      v4l2_fourcc('A', 'U', '1', '4')
> > +#define V4L2_AUDIO_FMT_IEC958_SUBFRAME_LE    v4l2_fourcc('A', 'U', '1', '8')
> > +#define V4L2_AUDIO_FMT_S24_3LE                       v4l2_fourcc('A', 'U', '3', '2')
> > +#define V4L2_AUDIO_FMT_U24_3LE                       v4l2_fourcc('A', 'U', '3', '4')
> > +#define V4L2_AUDIO_FMT_S20_3LE                       v4l2_fourcc('A', 'U', '3', '6')
> > +#define V4L2_AUDIO_FMT_U20_3LE                       v4l2_fourcc('A', 'U', '3', '8')
> > +
> > +#define v4l2_fourcc_to_audfmt(fourcc)        \
> > +     (__force snd_pcm_format_t)(((((fourcc) >> 16) & 0xff) - '0') * 10  \
> > +                                + ((((fourcc) >> 24) & 0xff) - '0'))
> > +
> >  /* priv field value to indicates that subsequent fields are valid. */
> >  #define V4L2_PIX_FMT_PRIV_MAGIC              0xfeedcafe
> >
>