linux-kernel - Re: [RFC PATCH 3/5] HACK: ASoC: Tolerate N-cpus-to-M-codecs links

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Message-ID: <YmamSZKNtNai7KyM@sirena.org.uk>
Date:   Mon, 25 Apr 2022 14:46:49 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Martin Povišer <povik@...ebit.org>
Cc:     Martin Povišer <povik+lin@...ebit.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mark Kettenis <kettenis@...nbsd.org>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>
Subject: Re: [RFC PATCH 3/5] HACK: ASoC: Tolerate N-cpus-to-M-codecs links

On Mon, Apr 25, 2022 at 03:11:14PM +0200, Martin Povišer wrote:
> > On 25. 4. 2022, at 14:55, Mark Brown <broonie@...nel.org> wrote:

> > I am surprised that doesn't otherwise explode TBH - at the very least
> > I'd expect it to show two PCMs to userspace which if I'm understanding
> > your description correctly isn't really what's going on.

> I fill in a single snd_soc_dai_link, it exposes a single PCM and works
> like a charm. That is as long as I patch the playback/capture check in
> question.

> I read that to be the clear intention of ASoC code: a DAI link becomes
> one snd_soc_pcm_runtime.

Yes, so long as you boil it down to a single link it works fine but the
bit on top of the binding where you tie the two CPU DAIs to what is
actually exposed is all in code.  The reason this stuff isn't filled in
is that connecting the thing that applications see to the physical links
isn't at all obvious and needs at least some driver sitting in the
middle to make the links - I'd imagine there's a DSP sitting there which
probably has quite a bit of flexability about how the various hardware
components available are actually related.  This makes figuring out what
to do with the relationship between the multiple CPU DAIs hard.

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