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

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Message-ID: <20180904155655.GJ12993@sirena.org.uk>
Date:   Tue, 4 Sep 2018 16:56:55 +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 10:10:24AM -0500, Andrew F. Davis wrote:
> On 09/04/2018 09:55 AM, Mark Brown wrote:

> > you get to keep the pieces" territory.  If we really want to have a way
> > of explicitly specifying that some widgets should never be turned on
> > then it feels like rather than have something device and widget specific
> > like this we should instead have a higher level way of doing that which
> > can be applied to any widget, that is something that could be useful
> > especially with things like speaker drivers where there's real potential
> > for physical damage to the system.

> Not sure how that could even look, it would need to be in DT as only
> that layer knows the connections, but then the it would also have to
> have internal knowledge of the widgets used in the driver..

We already have a bunch of DT code that knows about and uses the
external widgets the device has (which are I'd guess the only ones where
this is an issue)?  I was thinking just have a property that lists the
widgets that should never be turned on.

> > Like I said in my original reply I'm also worried that this will break
> > existing boards by causing them to change to a voltage of 0 when they
> > had managed to end up with the default of 2V which happened to work for
> > them.

> Then only time this could happen is if they specified MICBIAS_OFF in DT
> but got the default 2v instead. In which case, yes, the behavior would
> change, but it would also be changing to the correct behavior. We can't
> avoid fixing code on the off chance someone depended on the broken
> behavior, no progress could ever be made.

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

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