linux-kernel - Re: [PATCH 1/4] regulator: core: Support trying to get close to a certain voltage

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Message-ID: <20141211123106.GU11764@sirena.org.uk>
Date:	Thu, 11 Dec 2014 12:31:06 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Alexandru Stan <amstan@...omium.org>
Cc:	Doug Anderson <dianders@...omium.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Sonny Rao <sonnyrao@...omium.org>,
	Andrew Bresticker <abrestic@...omium.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, lgirdwood@...il.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] regulator: core: Support trying to get close to a
 certain voltage

On Wed, Dec 10, 2014 at 05:08:37PM -0800, Alexandru Stan wrote:
> The spec is from 1.7V to 1.95V, with 1.8V being ideal. It's not that
> symmetric. But let's say that 0.1V is fine for tolerance(so 1.7-1.9V)

Don't top post so people reading your message have some context to give
them some idea what you are talking about.

> Imagine a board has a 1V-1.79 V regulator, we tell it to
> regulator_set_voltage_tol(1800000,100000). It will try the 1.8V-1.9V
> range, when it sees that it can't it'll fallback to 1.7V - 1.9V, and
> it will just be lazy and pick the lowest of the range again:
> 1.7V(causing voltage drop issues because we're exactly at the minimum
> of the spec). The correct voltage would be 1.79V

This is just an implementation detail, everything you're saying here
applies equally to any user specifying by tolerance rather than range.
If the reason for doing this is to fix that problem then a new API isn't
the way to go about it.

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