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

[Nishanth Menon <nm@ti.com>]

On Fri, Feb 7, 2014 at 10:28 AM, Sudeep Holla <Sudeep.Holla@arm.com> wrote:
> On 07/02/14 16:15, Sudeep Holla wrote:
>> On 07/02/14 15:19, Thomas Abraham wrote:
>>> From: Thomas Abraham <thomas.ab@samsung.com>
>>>
>>> Add a new optional boost-frequency binding for specifying the frequencies
>>> usable in boost mode.
>>>
>>> Cc: Nishanth Menon <nm@ti.com>
>>> Cc: Lukasz Majewski <l.majewski@samsung.com>
>>> Cc: Rob Herring <robh+dt@kernel.org>
>>> Cc: Pawel Moll <pawel.moll@arm.com>
>>> Cc: Mark Rutland <mark.rutland@arm.com>
>>> Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
>>> Cc: Kumar Gala <galak@codeaurora.org>
>>> Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
>>> ---
>>>  Documentation/devicetree/bindings/cpufreq/cpufreq-boost.txt |   11 +++++++++++
>>>  1 file changed, 11 insertions(+)
>>>  create mode 100644 Documentation/devicetree/bindings/cpufreq/cpufreq-boost.txt
>>>
>>> diff --git a/Documentation/devicetree/bindings/cpufreq/cpufreq-boost.txt b/Documentation/devicetree/bindings/cpufreq/cpufreq-boost.txt
>>> new file mode 100644
>>> index 0000000..d925e38
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/cpufreq/cpufreq-boost.txt
>>> @@ -0,0 +1,11 @@
>>> +* Device tree binding for CPU boost frequency (aka over-clocking)
>>> +
>>> +Certain CPU's can be operated in optional 'boost' mode (or sometimes referred as
>>> +overclocking) in which the CPU can operate in frequencies beyond the normal
>>> +operating conditions.
>>> +
>>> +Optional Properties:
>>> +- boost-frequency: list of frequencies in KHz to be used only in boost mode.
>>> +  This list should be a subset of frequencies listed in "operating-points"
>>> +  property. Refer to Documentation/devicetree/bindings/power/opp.txt for
>>> +  details about "operating-points" property.
>>>
>>
>> Won't single entry for boost frequency suffice which would be the starting
>> frequency in the boost range. IOW will there be OPP list with frequencies:
>> A > B > C > D, but only B and C are boost frequency. That seems little odd,
>> unless it's some configuration chosen purely on software basis rather than
>> hardware. For me B marks the beginning of over-clocking.
>>
> Ah, I meant A < B < C < D in the above example.
Should'nt we let the SoC dts define that - traditionally, yes, but
consider the following:
A, B, C uses clk_parent X which describes B, C as overclocked.
and say D uses clk_parent Y which is not "over clocked", then you have
the scenario that on the first look seems counter-intutive.

Regards,
Nishanth Menon