linux-kernel - Re: [PATCH v6 3/8] cpufreq:acpi:x86: Adjust the acpi-cpufreq.c code to work with common boost solution

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Date:	Fri, 26 Jul 2013 11:44:14 +0200
From:	Lukasz Majewski <l.majewski@...sung.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, Zhang Rui <rui.zhang@...el.com>,
	Eduardo Valentin <eduardo.valentin@...com>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Jonghwa Lee <jonghwa3.lee@...sung.com>,
	Lukasz Majewski <l.majewski@...ess.pl>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Myungjoo Ham <myungjoo.ham@...sung.com>, durgadoss.r@...el.com
Subject: Re: [PATCH v6 3/8] cpufreq:acpi:x86: Adjust the acpi-cpufreq.c code to
 work with common boost solution

On Fri, 26 Jul 2013 14:54:07 +0530 Viresh Kumar viresh.kumar@...aro.org
wrote,
> On 26 July 2013 13:39, Lukasz Majewski <l.majewski@...sung.com> wrote:
> > On Fri, 26 Jul 2013 12:58:02 +0530 Viresh Kumar wrote,
> >> On 25 July 2013 22:03, Lukasz Majewski <l.majewski@...sung.com>
> >> wrote:
> >> > diff --git a/drivers/cpufreq/acpi-cpufreq.c
> >> > b/drivers/cpufreq/acpi-cpufreq.c
> >>
> >> >  static void __init acpi_cpufreq_boost_init(void)
> >> >  {
> >> > +       acpi_cpufreq_driver.boost_supported = false;
> >             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [*]
> >>
> >> Would be better if we do this in else of below if.
> >
> > We need to set boost_supported = false at [*] for the case when:
> > 1. msrs_alloc fails
> > or
> > 2. acpi_cpufreq is built as a module and can be inserted and removed
> > several times. Without [*] we could end up with wrong (not false)
> > initial state.
> 
> Hmm.. Now that I see the code again, we don't need to set it to false
> as it is a global variable and this field is already set to false..

Ok, so then I will remove this line [*].

> 
> >> >         if (boot_cpu_has(X86_FEATURE_CPB) ||
> >> > boot_cpu_has(X86_FEATURE_IDA)) { msrs = msrs_alloc();
> >>
> >>
> >> > @@ -1021,12 +995,11 @@ static int __init acpi_cpufreq_init(void)
> >> >                         *iter = &cpb;
> >> >         }
> >> >  #endif
> >> > +       acpi_cpufreq_boost_init();
> >             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [**]
> >>
> >> We are calling it before registering cpufreq driver. Will this have
> >> any complications?
> >
> > When we call [**] after the cpufreq_register_driver [***] we end up
> > with sysfs boost attribute not exported at x86.
> > The boost attribute is exported at [***] only when
> > acpi_cpufreq.boost_supported = true. However support for boost at
> > x86 is evaluated at acpi_cpufreq_boost_init().
> 
> I understand why you moved it above cpufreq driver register. I was
> thinking if there can be few side effects of this..

As fair as I've tested it, there weren't any side effects. 

Moreover the acpi_cpufreq_boost_init() mostly read state of the HW, so
IMHO can be done before cpufreg_register_driver(). 

-- 
Best regards,

Lukasz Majewski

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