linux-kernel - Re: [PATCH 2/6] ARM: Tegra: Add CPU's OPPs for using cpufreq-cpu0 driver

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Date:	Thu, 8 Aug 2013 10:52:57 -0500
From:	Nishanth Menon <nm@...com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Lucas Stach <l.stach@...gutronix.de>,
	Mark Rutland <Mark.Rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linaro-kernel@...ts.linaro.org, swarren@...dia.com,
	Ian Campbell <ian.campbell@...rix.com>,
	Pawel Moll <pawel.moll@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	cpufreq@...r.kernel.org, rjw@...k.pl,
	Rob Herring <rob.herring@...xeda.com>, patches@...aro.org,
	mturquette@...aro.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/6] ARM: Tegra: Add CPU's OPPs for using cpufreq-cpu0 driver

On Thu, Aug 8, 2013 at 9:37 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On 8 August 2013 19:52, Lucas Stach <l.stach@...gutronix.de> wrote:
>> You can certainly define the mapping table in DT where a specialized
>> Tegra cpufreq driver could read it in and then map frequency to voltage.
>> But that's a runtime decision, as Speedo and process ID are fuse values
>> and can not be represented in DT.
>
>> The problem with this is that the hardware description now associates
>> voltages with certain frequencies and even if they are not used by the
>> Linux driver they are plain wrong.
>
> Hmm. I understand.
> Then we probably need mach-tegra/opp.c to call opp_add() for all such
> OPPs.. Neither DT nor cpufreq driver are the right place for this.

This is similar to what I suspected might be the case on other
platforms (in addition to known iMx and OMAP). Could you see/comment
on [1] to see if it meets your needs.

We should like to avoid dealing custom SoC specific OPP, if we are
able to generalize the need.  ofcourse, I am yet to submit a official
proposal, but more SoCs the current proposal can handle, the better it
will be for all of us.

[1] http://marc.info/?l=linux-pm&m=137589225305971&w=2
--
Regards,
Nishanth Menon
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