linux-kernel - Re: [PATCH v3 1/3] cpufreq: Add boost frequency support in core

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Date:	Thu, 20 Jun 2013 08:41:08 +0200
From:	Lukasz Majewski <l.majewski@...sung.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Jonghwa Lee <jonghwa3.lee@...sung.com>,
	Myungjoo Ham <myungjoo.ham@...sung.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Lukasz Majewski <l.majewski@...ess.pl>,
	Andre Przywara <andre.przywara@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Amit Daniel Kachhap <amit.daniel@...sung.com>
Subject: Re: [PATCH v3 1/3] cpufreq: Add boost frequency support in core

On Thu, 20 Jun 2013 10:41:41 +0530, Viresh Kumar wrote:
> On 19 June 2013 12:46, Lukasz Majewski <l.majewski@...sung.com> wrote:
> > I would like to clarify the above issue.
> >
> > When I've discussed with Viresh previous version of this patch, we
> > have agreed, that "boost" sysfs attribute [*]:
> > /sys/devices/system/cpu/cpufreq/boost
> >
> > would be only visible when boost_supported flag is set at cpufreq
> > driver.
> 
> Yes.
> 
> > When acpi-cpufreq driver doesn't support boost, the attribute [*]
> > won't be exported at all. This contradicts the documentation and
> > legacy acpi-cpufreq behaviour.
> 
> No they aren't contradictory. What the documentation meant was:
> acpi-cpufreq driver is used by lots of different x86 processors. Now
> all processors might not support boost inside x86 also. And for them
> we will keep 'boost' file readonly. This is done by following
> statement

Thanks for explanation.

> 
> 	if (boot_cpu_has(X86_FEATURE_CPB) ||
> boot_cpu_has(X86_FEATURE_IDA)) { boost_supported = true;
>                 ....
> 	} else
> 		global_boost.attr.mode = 0444;

Grrr.... So simple and obvious solution [1]. 

> 
> Documentation file doesn't talk about any other cpufreq driver, for
> them there is no concept like boost.
> 
> You need to preserve this functionality.

Yes the idea [1], solves problem with legacy API.

> 
> > Since I'm affraid to break API (with all its consequences :-) ), I
> > would like to be sure that this is OK, and thereof I'm allowed to
> > rewrite documentation accordingly.
> >
> > I simply need explicit permission from both maintainers :-).
> 
> For me its okay to rewrite documentation.

I will extent documentation about the SW managed boost.

-- 
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group
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