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

[Lukasz Majewski <l.majewski@samsung.com>]

Hi Thomas, Sudeep,

> On Sat, Feb 8, 2014 at 1:11 AM, Nishanth Menon <nm@ti.com> wrote:
> > On Fri, Feb 7, 2014 at 12:02 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.
> >>
> >> 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.
> > Fair enough - but i still think it has nothing to do with dt binding
> > itself -> and i think the discussion we've had should be good for
> > the binding provided in this patch.. I hope.. if documentation
> > needs a bit of better explanation to prevent a repeat of the same
> > discussion at a later point of time, now might be a good time to
> > add it in.
> 
> The term boost and over-clocking have been described in the bindings
> document as being the same. Since the term over-clocking refers to
> running a CPU beyond normal operating frequencies, I tend to agree
> with Sudeep that it is not intuitive if a normal operating frequency
> is greater than a boost mode frequency.
> 
> Otherwise, when userspace does "echo 1 >
> /sys/devices/system/cpu/cpufreq/boost", what is it supposed to mean. I
> think the original intent of boost mode patches was to allow CPU to
> operate at frequencies greater than the normal operating frequencies.
> 
> Lukasz, how would you want this to be handled?

Please consider an example:

normal-freqs: 1400000, 1200000, 1000000, 800000, 600000, 400000, 200000
[1]
boost-freqs: 1700000, 1600000, 1500000. [2]

All those freqs shall be represented as OPPs freq and voltage tuple.

Best would be to specify all the boost-freqs as:
boost-freqs = <1700000 1600000 1500000> to be prepared for future
quirks or problems (or special cases which might show up latter).
If anybody can foresee any potential threads - like platform on which
boost freqs are 1700000 and 1500000, but not 1600000, then please share
this information.

However, I think that it would be also acceptable to specify only:
boost-freq = <1500000> and mark all freqs greater or equal to it as
CPUFREQ_BOOST_FREQ.

If there aren't any potential problems, then I think the second option
would be a good solution (we would have only one BOOST attribute stored
at CPUs DTS node).

> 
> Thanks,
> Thomas.
> 
> >
> > Regards,
> > Nishanth Menon
> 
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-- 
Best regards,

Lukasz Majewski

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