linux-kernel - Re: [RFC PATCH v3 6/9] media: v4l2: Add audio capture and output support

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Message-ID: <ZQmLuo5OwvttG0sR@valkosipuli.retiisi.eu>
Date:   Tue, 19 Sep 2023 11:53:30 +0000
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Shengjiu Wang <shengjiu.wang@...il.com>
Cc:     Shengjiu Wang <shengjiu.wang@....com>, hverkuil@...all.nl,
        tfiga@...omium.org, m.szyprowski@...sung.com, mchehab@...nel.org,
        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: [RFC PATCH v3 6/9] media: v4l2: Add audio capture and output
 support

Hi Shengjiu,

On Tue, Sep 19, 2023 at 06:31:09PM +0800, Shengjiu Wang wrote:

...

> > > +*************************
> > > +V4L2_AUDIO_FMT_LPCM ('LPCM')
> > > +*************************

Something to fix here, too...?

> > > +
> > > +Linear Pulse-Code Modulation (LPCM)
> > > +
> > > +
> > > +Description
> > > +===========
> > > +
> > > +This describes audio format used by the audio memory to memory driver.
> > > +
> > > +It contains the following fields:
> > > +
> > > +.. flat-table::
> > > +    :widths: 1 4
> > > +    :header-rows:  1
> > > +    :stub-columns: 0
> > > +
> > > +    * - Field
> > > +      - Description
> > > +    * - u32 samplerate;
> > > +      - which is the number of times per second that samples are taken.
> > > +    * - u32 sampleformat;
> > > +      - which determines the number of possible digital values that can be used to represent each sample
> >
> > 80 characters (or less) per line, please.
> 
> Ok, will change it.
> 
> >
> > Which values could this field have and what do they signify?
> 
> The values are SNDRV_PCM_FORMAT_S8, SNDRV_PCM_FORMAT_U8...
> which are the PCM format, defined in ALSA.

I suppose this is documented in ALSA documentation. Could you refer to
that?

> 
> >
> > > +    * - u32 channels;
> > > +      - channel number for each sample.
> >
> > I suppose the rest of the buffer would be samples? This should be
> > documented. I think there are also different ways the data could be
> > arrangeed and this needs to be documented, too.
> 
> All data in the buffer are the samples,  the 'samplerate', 'sampleformat'
> 'channels'  I list here is try to describe the samples.
> I was confused how to write this document, so I list the characters.

The layout of this data in memory needs to be documented. I think a
reference to ALSA documentation would be the best.

-- 
Regards,

Sakari Ailus