Re: [PATCH v2 2/2] Documentation: devicetree: Add boost-frequency binding to list boost mode frequency

Lukasz Majewski
2014-02-10T07:38:36Z

Hi Thomas, Sudeep,

> On Fri, Feb 7, 2014 at 11:32 PM, Sudeep Holla <Sudeep.Holla@arm.com>
> wrote:
> > On 07/02/14 17:37, Nishanth Menon wrote:
> >> On Fri, Feb 7, 2014 at 11:31 AM, Sudeep Holla
> >> <Sudeep.Holla@arm.com> wrote:
> >
> > [...]
> >
> >>> Yes I think its counter-intuitive as it's visible to the
> >>> userspace(list of frequencies and the boost parameters are
> >>> exposed through sysfs)
> >>
> >> That will be a different problem -> as currently every single
> >> frequency in the cpufreq list has ability to be marked as boost
> >> frequency - if userspace does not maintain that, then, IMHO, fix
> >> the userspace :D
> >>
> >
> > /sys/devices/system/cpu/cpu*/cpufreq/scaling_available_frequencies
> > gives the list of frequencies based on the state of the boost
> > feature at anytime.
>
> The list of frequencies in
> /sys/devices/system/cpu/cpu*/cpufreq/scaling_available_frequencies
> does not change based in the state of the boost feature (enabled or
> disabled). But the scaling_max_frequency and scaling_min_frequency are
> updated based on the set of available + boost frequencies available.

With boost intended behavior is as follow:

/sys/devices/system/cpu/cpu*/cpufreq/scaling_available_frequencies [1]

shows the non boost frequencies no matter if boost is enabled or not.
Those are the "normal" frequencies.

When boost is supported (by enabling the CONFIG_CPU_FREQ_BOOST_SW)
extra sysfs attribute shows up:

/sys/devices/system/cpu/cpu0/cpufreq/scaling_boost_frequencies [2]
in which are listed only the boost frequencies.

If the dts doesn't provide any values or as it is now no
CPUFREQ_BOOST_FREQ flag is specified (at exynos4x12-cpufreq.c), then
this list is empty.

When boost is disabled the max freq (cpuinfo_max_freq) is in the range
listed at [1].

When boost is enabled this value is the sum of freqs represented at [1]
and [2].

By adding an extra attribute [2] we:
1. Indicate that boost is supported
2. List provided BOOST frequencies
3. Separate boost and non boost freqs

>
> >
> > Intuitively the list without boost shouldn't have any frequency
> > above the range when it's enabled :), that's what I was referring
> > to. So I am not talking about any issue with user-space maintenance.
> >
> > Regards,
> > Sudeep
> >

--
Best regards,

Lukasz Majewski

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