linux-kernel - Re: [PATCH 4/4] ASoC: wm8904: add DMIC support

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Message-ID: <YrC2tLI+nUxOGsIX@sirena.org.uk>
Date:   Mon, 20 Jun 2022 19:04:36 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Pierluigi Passaro <pierluigi.p@...iscite.com>
Cc:     Alifer Willians de Moraes <alifer.m@...iscite.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Eran Matityahu <eran.m@...iscite.com>,
        "festevam@...il.com" <festevam@...il.com>,
        "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "nicoleotsuka@...il.com" <nicoleotsuka@...il.com>,
        "patches@...nsource.cirrus.com" <patches@...nsource.cirrus.com>,
        "perex@...ex.cz" <perex@...ex.cz>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "shengjiu.wang@...il.com" <shengjiu.wang@...il.com>,
        "tiwai@...e.com" <tiwai@...e.com>,
        "Xiubo.Lee@...il.com" <Xiubo.Lee@...il.com>
Subject: Re: [PATCH 4/4] ASoC: wm8904: add DMIC support

On Mon, Jun 20, 2022 at 05:52:43PM +0000, Pierluigi Passaro wrote:
> > > Just for my understanding, are you suggesting to set a device tree
> > > property to force a fixed behavior in the driver ?

> > Yes.

> Why should we use a fixed behavior ?

The things that are fixed by the design should be fixed.

> > The device shares pins between the line inputs and the DMIC inputs so at
> > least some of the configuration is going to be determinted at system
> > design time, that will fix the usable values of at least one of the
> > controls which ought to be reflected in the runtime behaviour.

> In our design we use:
> - pin 1: DMIC_CLK
> - pin 24: LINEIN2R
> - pin 26: LINEIN2L
> - pin 27: DMIC_DATA

> we have no pins shared among DMIC and LINEIN.

This means that DMICDAT2 is not usefully selectable at runtime, you've
got IN1 as digital and IN2 as analogue, so while the DMIC/ADC switch is
useful the DMIC1/2 switch is not.

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