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

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Message-ID: <43f0ecdf-7454-49ae-96b3-2eae5487e9a5@sirena.org.uk>
Date:   Mon, 3 Jul 2023 13:53:51 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Shengjiu Wang <shengjiu.wang@...il.com>,
        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, 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, Jul 03, 2023 at 02:07:10PM +0200, Takashi Iwai wrote:
> Shengjiu Wang wrote:

> > 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.

Yeah, it's not a terrible idea.  We might use it more if we ever get
better support for DSP audio, routing between the DSP and external
devices if driven from the CPU would be a memory to memory thing.

> 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.

I've still not looked at the code at all.

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