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

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Date:	Fri, 01 Mar 2013 13:49:01 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Bill Huang <bilhuang@...dia.com>
CC:	Mike Turquette <mturquette@...aro.org>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>,
	"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>
Subject: Re: [PATCH 2/5] clk: notifier handler for dynamic voltage scaling

On 03/01/2013 02:41 AM, Bill Huang wrote:
> 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.

Perhaps that "just" means extending the dvfs.c code here to iterate over
each clock consumer (rather than each clock provider), and having each
set a minimum voltage (rather than a specific voltage), and having the
regulator core apply the maximum of those minimum constraints?

Or something like that anyway.
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