linux-kernel - Re: Shared regulator usage

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Message-ID: <20121127113221.GB4468@opensource.wolfsonmicro.com>
Date:	Tue, 27 Nov 2012 11:32:21 +0000
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Anirudh Ghayal <aghayal@...eaurora.org>
Cc:	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	collinsd@...eaurora.org, khilman@...com, tsoni@...eaurora.org
Subject: Re: Shared regulator usage

On Tue, Nov 27, 2012 at 04:45:29PM +0530, Anirudh Ghayal wrote:

> At 1.4Ghz the cpu-freq driver votes for 1.3v, then the CPR kicks in
> and recommends a voltage of 1.275v. Now a set_voltage with this new
> level (1.275v, 1.275)  fails as it does not satisfy the limits of
> the cpu-freq driver. It is not possible to tweak this range any
> further as it would not achieve the goal of micro-adjusting the
> voltage to save power.

> Such scenarios are very likely to occur in the future on embedded
> systems where there is a need to conserve power by introducing some
> adaptive voltage scaling techniques based on various parameters such
> as temperature/sensitivity.

This just sounds like bad software design.  You've got two unrelated
drivers setting the same thing without talking to each other even though
the one is trying to adjust the voltage set by the other without
actually knowing the voltage that the other one set.  Why are these
separate drivers?

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