linux-kernel - Re: [PATCH 1/4] ASoC: dt-bindings: document new symmetric-clock-role flag

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Message-ID: <91b6d02a-25d5-4835-942e-3f8072bd8897@sirena.org.uk>
Date:   Fri, 2 Jun 2023 13:19:08 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Alvin Šipraga <ALSI@...g-olufsen.dk>
Cc:     Alvin Šipraga <alvin@...s.dk>,
        Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] ASoC: dt-bindings: document new symmetric-clock-role
 flag

On Fri, Jun 02, 2023 at 12:12:52PM +0000, Alvin Šipraga wrote:
> On Fri, Jun 02, 2023 at 12:43:51PM +0100, Mark Brown wrote:

> > Why would we have a property for this and not just describe whatever the
> > actual clocking arrangement is?

> Sure - let me just elaborate on my thinking and maybe you can help me with a
> better approach:

> The clocking arrangement is encoded in the dai_fmt field of snd_soc_dai_link,
> but this is a single value that describes the format on both ends. The current
> behaviour of ASoC is to flip the clock roles encoded in dai_fmt when applying it
> to the CPU side of the link.

> Looking from a DT perspective, if I do not specify e.g. bitclock-master on
> either side of the link, then the dai_fmt will describe the codec as a bitclock
> consumer and (after flipping) the CPU as a provider. That's the default
> implication of the DT bindings and I can't break compatibility there.

None of this addresses my question.  To repeat why would we not just
describe the actual clocking arrangement here - this property does not
specify where the clock actually comes from at all, we're still going to
need additional information for that and if we've described that clock
then we already know it's there without having to specify any more
properties.

> The other issue is that for the simple-card the DAI format is only parsed in one
> place and applied to the whole link. Are you proposing that it be modified to
> explicitly try and parse both ends in order to determine if both sides want to
> be clock consumers? In that case I'd have to also introduce bitclock-consumer
> and frameclock-consumer properties to mirror the existing bitclock-master and
> frameclock-master properties, as an explicit absence of the *-master property on
> both sides would have to default to the original ASoC behaviour described above.

If simple-card can't be made to work that's fine, it's deprecated
anyway.

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