linux-kernel - Re: Voltage setting on chained regulators, how?

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Message-ID: <20150925164726.GI30445@sirena.org.uk>
Date:	Fri, 25 Sep 2015 09:47:26 -0700
From:	Mark Brown <broonie@...nel.org>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	Liam Girdwood <lgirdwood@...il.com>, kernel@...gutronix.de,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: Voltage setting on chained regulators, how?

On Fri, Sep 25, 2015 at 11:07:24AM +0200, Sascha Hauer wrote:

> Any idea how such a scenario could be implemented? The regulator
> framework already has some idea of supply regulators, but it only takes
> care of en/disabling the supplies and will not change the voltage on the
> supplies. Should this be implemented in the regulator framework?  Some
> first experiments brought me into a locking hell quite fast.

It's just a case of implementation, but yes the locking is fun.  I don't
think it's that big a deal to rethink it, it's partly complicated since
the existing locking is designed to be really simple and easy to review.

> For added fun ideally we want to put the LDOs in bypass mode instead of
> configuring them for minimum dropout. The bypass mode doesn't work for
> the 1.2GHz operating point though since the ripple on the switching
> regulator gets too high. So we can't just statically configure bypass
> mode but have to enable it dynamically based on the operating points.

I suspect you always want the LDO in there to clean the supply up, it's
just a more serious issue when more power is being drawn.  Having a DCDC
doing most of the voltage drop for efficiency with a LDO to clean up the
output of the DCDC is pretty common.

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