linux-kernel - Re: [PATCH 1/1] cpufreq: cpufreq-cpu0: use the max voltage instead of voltage-tolerance

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Message-ID: <20131106032742.GP19770@S2101-09.ap.freescale.net>
Date:	Wed, 6 Nov 2013 11:27:44 +0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Rongjun Ying <Rongjun.Ying@....com>
CC:	Viresh Kumar <viresh.kumar@...aro.org>, rjying <rjying@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"rongjun.ying@...r.com" <rongjun.ying@...r.com>
Subject: Re: [PATCH 1/1] cpufreq: cpufreq-cpu0: use the max voltage instead
 of voltage-tolerance

On Wed, Nov 06, 2013 at 02:15:07AM +0000, Rongjun Ying wrote:
> If omit voltage-tolerance, sometimes also can't get appropriate voltages.
> For example:
> If the regulator IC only can supply min voltage is 1.000V and max voltage is 1.200V, and cpu work max voltage is 1.200V.
> But the cpu just need 1.100V when cpu run under a freq.
> So regulator_set_voltage_tol will return failed. 
> Because the regulator_set_voltage will invoke with min-uV is 1100000 and max-uV is 1100000 parameters.
> Regulator can't supply it.
> As this case, the regulator just need supply 1.200V.

For given board, what voltages could be provided is known.  So you can
just define OPP table in <board>.dts and specify the voltage as the
value that the regulator IC can supply, e.g. 1.200V in above example.

This is not nice, as OPP table is CPU/SoC specific and should be ideally
defined in <soc>.dtsi.  But still it's a way out for you to use
cpufreq-cpu0 driver as it is.

In any case, you can not just change voltage-tolerance to voltage-max
with no care about the existing users.

Shawn

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