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

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Date:   Tue, 4 Sep 2018 09:43:03 -0500
From:   "Andrew F. Davis" <afd@...com>
To:     Mark Brown <broonie@...nel.org>
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 09/04/2018 09:41 AM, Mark Brown wrote:
> On Tue, Sep 04, 2018 at 08:55:06AM -0500, Andrew F. Davis wrote:
>> On 09/03/2018 06:26 AM, Mark Brown wrote:
> 
>>> If we really want to pay attention to something setting this up we'd
>>> need to completely remove the widget - what the code is doing at the
>>> minute is setting the voltage that the bias will go to when enabled,
>>> there's still a widget for turning it on and off.  There's some chance
>>> that this will break existing boards.
> 
>> Turning on bias is controlled separately, automatically in user-space in
>> many cases, not based on the board. The DT needs to have a way to state
>> that 0v is the needed bias on this board, without this you can not set
>> 0v bias and 2v is chosen by default (which is IMHO should be 0v but that
>> would change existing behavior so I won't touch that).
> 
> Surely turning on MICBIAS at 0V is equivalent to leaving the bias off?
> 

It is, but DT doesn't control when or why MICBIAS is turned on or off,
only what voltage on should be.