linux-kernel - Re: [PATCH v6 5/8] cpufreq:boost:Kconfig: Provide support for software managed BOOST

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Date:	Fri, 26 Jul 2013 13:21:20 +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>, durgadoss.r@...el.com
Subject: Re: [PATCH v6 5/8] cpufreq:boost:Kconfig: Provide support for software
 managed BOOST

On Fri, 26 Jul 2013 15:54:56 +0530 Viresh Kumar wrote,
> On 25 July 2013 22:03, Lukasz Majewski <l.majewski@...sung.com> wrote:
> > For safety reasons new flag - CONFIG_CPU_FREQ_BOOST_SW has been
> > added. Only after selecting "EXYNOS Frequency Overclocking -
> > Software" Kconfig
> 
> You shouldn't mention Exynos here and must do exynos stuff at the end
> in a separate patch. This one must be generic.

Please see below comments.

> 
> > option the software managed boost is enabled. It also selects
> > thermal subsystem to be compiled in. Thermal is necessary for
> > disabling boost and cooling down the device when overheating
> > detected.
> >
> > Boost _MUST_NOT_ work without thermal subsystem with properly
> > defined overheating temperatures.
> >
> > This option doesn't affect x86's ACPI hardware managed boost support
> > (i.e. Intel, AMD). In this situation boost management is embedded at
> > hardware.
> >
> > Signed-off-by: Lukasz Majewski <l.majewski@...sung.com>
> > Signed-off-by: Myungjoo Ham <myungjoo.ham@...sung.com>
> >
> > ---
> > Changes for v6:
> > - CPU_FREQ_BOOST_SW [1] is now defined as "invisible" bool option.
> > - Platform dependent ARM_EXYNOS_CPU_FREQ_BOOST_SW config option has
> > been added. It depends on ARM_EXYNOS_CPUFREQ options and selects
> >   EXYNOS_THERMAL with the main boost config [1].
> >
> > Changes for v5:
> > - New patch
> >
> >  drivers/cpufreq/Kconfig     |    3 +++
> >  drivers/cpufreq/Kconfig.arm |   16 ++++++++++++++++
> >  2 files changed, 19 insertions(+)
> >
> > diff --git a/drivers/cpufreq/Kconfig b/drivers/cpufreq/Kconfig
> > index 534fcb8..3f058a3 100644
> > --- a/drivers/cpufreq/Kconfig
> > +++ b/drivers/cpufreq/Kconfig
> > @@ -23,6 +23,9 @@ config CPU_FREQ_TABLE
> >  config CPU_FREQ_GOV_COMMON
> >         bool
> >
> > +config CPU_FREQ_BOOST_SW
> > +       bool
> 
> Invisible is fine but this must be disabled by default and must
> depend on thermal, rather than moving dependency on platform's
> config.

The CPU_FREQ_BOOST_SW [1] is a generic flag (invisible).

I will add "default n" to it.
It shall be used at all BOOST dependent #ifdefs (generic + platform).



Also I've introduced the ARM_EXYNOS_CPU_FREQ_BOOST_SW [2] config
option. The CPU_FREQ_BOOST_SW option is selected from it.

Moreover the [2] depends on ARM_EXYNOS_CPUFREQ (which prevents from
accidental enable/disable). And it selects automatically the
EXYNOS_THERMAL, which is much better than depending only on THERMAL [3]
(the generic framework).

Depending only on [3], results at situation where SW BOOST can be
enabled at x86 or ARM target with only generic THERMAL support (which
doesn't protect from overheating).


So the proposed solution:
1. Defines global flag [1]
2. This flag is selected only when dependencies for more HW close flag
[2] are meet.
3. It is more natural to have Kconfig BOOST enable/disable checkbox at
platform cpufreq driver (with description closer to HW).
4. Other ARCHs can easily define similar to [2] flag and by it select
[1].

For me the approach proposed in this patch is more natural and provides
high protection level from accidental SW boost enable.

-- 
Best regards,

Lukasz Majewski

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