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

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Message-ID: <AM6PR08MB4376411B180D8860E2AD3AE0FFB09@AM6PR08MB4376.eurprd08.prod.outlook.com>
Date:   Mon, 20 Jun 2022 19:53:56 +0000
From:   Pierluigi Passaro <pierluigi.p@...iscite.com>
To:     Alifer Willians de Moraes <alifer.m@...iscite.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "broonie@...nel.org" <broonie@...nel.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

> > > > 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.

A customer could have the following working configuration
- pin 1: DMIC_CLK
- pin 24: LINEIN2R
- pin 25: DMICDAT2
- pin 26: LINEIN2L
- pin 27: DMICDAT1
with no shared pins: here there's the chance to select DMIC1, DMIC2 and
LINEIN2 at runtime: I can't find a reason for a fixed behavior.
Can you please elaborate ?