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

From: Rongjun Ying <Rongjun.Ying@csr.com>
To: Shawn Guo <shawn.guo@linaro.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>, rjying <rjying@gmail.com>,
	"Rafael J. Wysocki" <rjw@sisk.pl>,
	"cpufreq@vger.kernel.org" <cpufreq@vger.kernel.org>,
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Barry Song <Barry.Song@csr.com>
Subject: RE: [PATCH 1/1] cpufreq: cpufreq-cpu0: use the max voltage instead of voltage-tolerance
Date: Thu, 7 Nov 2013 01:55:21 +0000	[thread overview]
Message-ID: <86130EF012BDF348AA0D464A4F44947801295427BD@SHAASIEXM01.ASIA.ROOT.PRI> (raw)
In-Reply-To: <20131106032742.GP19770@S2101-09.ap.freescale.net>

> -----Original Message-----
> From: Shawn Guo [mailto:shawn.guo@linaro.org]
> Sent: Wednesday, November 06, 2013 11:28 AM
> To: Rongjun Ying
> Cc: Viresh Kumar; rjying; Rafael J. Wysocki; cpufreq@vger.kernel.org;
> linux-pm@vger.kernel.org; Linux Kernel Mailing List;
> rongjun.ying@gcsr.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
> 
I don't think so. The voltage/freq pairs are attribute of the CPU.
Any boards can choose regulator IC base the cost and other reasons.
If the opp table defined in <board>.dts, we can set exact voltage/freq pairs,
and not need use the voltage-tolerance to set tolerance.

Thanks
-RongJun Ying
> 
> 
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