linux-kernel - Re: [PATCH 1/6] media: v4l2: Add audio capture and output support

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Message-ID: <87h6ql5hch.wl-tiwai@suse.de>
Date:   Mon, 03 Jul 2023 14:07:10 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Shengjiu Wang <shengjiu.wang@...il.com>
Cc:     Sakari Ailus <sakari.ailus@....fi>,
        Shengjiu Wang <shengjiu.wang@....com>, 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, hverkuil@...all.nl,
        Jacopo Mondi <jacopo@...ndi.org>
Subject: Re: [PATCH 1/6] media: v4l2: Add audio capture and output support

On Mon, 03 Jul 2023 11:54:22 +0200,
Shengjiu Wang wrote:
> 
> 
> Hi Sakari
> 
> On Fri, Jun 30, 2023 at 6:05 PM Sakari Ailus <sakari.ailus@....fi> wrote:
> 
>     Hi Shengjiu,
>    
>     On Thu, Jun 29, 2023 at 09:37:48AM +0800, 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.
>    
>     Why are you proposing to add this to V4L2 framework instead of doing this
>     within ALSA?
>    
>     Also cc Hans and Jacopo.
> 
> There is no such memory to memory interface defined in ALSA.  Seems
> ALSA is not designed for M2M cases.

There is no restriction to implement memory-to-memory capture in ALSA
framework.  It'd be a matter of the setup of PCM capture source, and
you can create a corresponding kcontrol element to switch the mode or
assign a dedicated PCM substream, for example.  It's just that there
was little demand for that.

I'm not much against adding the audio capture feature to V4L2,
though, if it really makes sense.  But creating a crafted /dev/audio*
doesn't look like a great idea to me, at least.


thanks,

Takashi