linux-kernel - Re: [PATCH] ASoC: tlv320aic31xx: Add MICBIAS off setting

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Message-ID: <20180904162101.GK12993@sirena.org.uk>
Date:   Tue, 4 Sep 2018 17:21:01 +0100
From:   Mark Brown <broonie@...nel.org>
To:     "Andrew F. Davis" <afd@...com>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        alsa-devel@...a-project.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ASoC: tlv320aic31xx: Add MICBIAS off setting

On Tue, Sep 04, 2018 at 11:02:14AM -0500, Andrew F. Davis wrote:
> On 09/04/2018 10:56 AM, Mark Brown wrote:

> > I'm really having a lot of trouble seeing MICBIAS_OFF as a useful
> > voltage to specify in DT in the first place.

> I don't see the usefulness in specifying any bias voltage in DT at all,
> it is a configuration and can be made at runtime, it has no place in DT.
> But it is already here, so lets allow all available voltages a board may
> need and the CODEC can supply, even 0.

It is very rare for it to be useful to select the bias voltage at
runtime - it's usually something that's decided by the electrical
engineering at system design time and linked to selection of passive
components rather than something that a user could usefully vary.  I
suspect in the situations where it is useful to vary it you'd want a
layer of indirection mapping it onto some user observable behaviour (or
the system should just do this autonomously as with the various low
power mic detect solutions out there).  What situations are you aware of
where runtime configuration is useful?

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