linux-kernel - Re: [PATCH 2/5] clk: notifier handler for dynamic voltage scaling

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Date:	Fri, 1 Mar 2013 01:41:31 -0800
From:	Bill Huang <bilhuang@...dia.com>
To:	Mike Turquette <mturquette@...aro.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>
Subject: Re: [PATCH 2/5] clk: notifier handler for dynamic voltage scaling

On Thu, 2013-02-28 at 12:49 +0800, Mike Turquette wrote:
> Dynamic voltage and frequency scaling (dvfs) is a common power saving
> technique in many of today's modern processors.  This patch introduces a
> common clk rate-change notifier handler which scales voltage
> appropriately whenever clk_set_rate is called on an affected clock.

I really think clk_enable and clk_disable should also be triggering
notifier call and DVFS should act accordingly since there are cases
drivers won't set clock rate but instead disable its clock directly, do
you agree?
> 
> There are three prerequisites to using this feature:
> 
> 1) the affected clocks must be using the common clk framework
> 2) voltage must be scaled using the regulator framework
> 3) clock frequency and regulator voltage values must be paired via the
> OPP library

Just a note, Tegra Core won't meet prerequisite #3 since each regulator
voltage values is associated with clocks driving those many sub-HW
blocks in it.


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