linux-kernel - Re: [RFC 5/8] regulator: anatop: fix min dropout for bypass mode

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Date:   Tue, 28 Mar 2017 14:52:46 +0300
From:   Leonard Crestez <leonard.crestez@....com>
To:     Mark Brown <broonie@...nel.org>
CC:     Liam Girdwood <lgirdwood@...il.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Shawn Guo" <shawnguo@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Robin Gong <yibin.gong@....com>,
        Anson Huang <Anson.Huang@....com>,
        Irina Tirdea <irina.tirdea@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Fabio Estevam <fabio.estevam@....com>,
        "Octavian Purdila" <octavian.purdila@....com>,
        <linux-pm@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 5/8] regulator: anatop: fix min dropout for bypass mode

On Fri, 2017-03-24 at 12:54 +0000, Mark Brown wrote:
> On Wed, Mar 22, 2017 at 06:53:07PM +0200, Leonard Crestez wrote:
> > +	if (anatop_reg->bypass)
> > +		anatop_reg->rdesc.min_dropout_uV = 0;
> > +	else
> > +		anatop_reg->rdesc.min_dropout_uV = LDO_MIN_DROPOUT_UV;
> No, this is completely broken - you can't expect to randomly change hthe
> regulator description at runtime behind the back of the framework and
> expect things to work.  If there is a need to do this we need an
> interface for getting the current value and a way to notify of changes.
> 
> That said I would not expect the dropout voltage to be considered at
> all when the regulator is bypassed, since the regulator is not
> regulating it doesn't need any headroom.

It's a more complex solution but this could be handled in the core instead.
Basically the core would treat min_dropout_uV as zero if the regulator is
currently in bypass mode.

In theory a function could be added in regulator_ops to ask a regulator driver
what requirements it has for its supply but this does not seem necessary.