linux-kernel - Re: [PATCH 4/6] regulator: core: Propagate voltage changes to supply regulators

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Message-ID: <20151002173256.GZ12635@sirena.org.uk>
Date:	Fri, 2 Oct 2015 18:32:56 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	linux-kernel@...r.kernel.org, Liam Girdwood <lgirdwood@...il.com>,
	kernel@...gutronix.de, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 4/6] regulator: core: Propagate voltage changes to supply
 regulators

On Wed, Sep 30, 2015 at 04:05:44PM +0200, Sascha Hauer wrote:

> A new min_dropout_uv field is added to struct regulator_desc. Regulators
> can specify the minimun dropout voltage they need for proper function
> here. Now when the voltage is changed on a regulator the regulator core
> makes sure that

Can we have this interface addition as a separate patch please?  Makes
it easier to add to other devices.  I could've sworn I'd already done
that bit but obviously never got the patch mailed out.

One change I think we need here is only doing the propagation if either
the device lacks a set_voltage() operation (in which case it's just a
switch passing through the parent voltage) or we have a dropout voltage,
otherwise we'll try to set the exact voltage the regulator is supposed
to output and that'll most likely end in tears.  Otherwise this is
making sense to me.

> Calculating the optimum voltage for the supply regulator is a bit tricky
> since the simple approach of just adding the desired minimum voltage and
> the minimum dropout is not enough. It may happen that the current
> regulator does not support the desired minimum voltage, but only a
> higher one. This means we have to figure out the lowest voltage
> supported by the regulator that is higher than the minimum desired
> voltage. The regulator_get_voltage_floor introduced with this patch does
> exactly that.

Yeah, split out the calcuate and the set.

Thanks for working on this!

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