linux-kernel - Re: [PATCH V6 1/9] PM / OPP: Introduce "power-domain-opp" property

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Date:   Sat, 06 May 2017 11:39:08 +0200
From:   Kevin Hilman <khilman@...libre.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Rob Herring <robh@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>, ulf.hansson@...aro.org,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        lina.iyer@...aro.org, rnayak@...eaurora.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH V6 1/9] PM / OPP: Introduce "power-domain-opp" property

Sudeep Holla <sudeep.holla@....com> writes:

> On 28/04/17 21:48, Rob Herring wrote:
>> On Wed, Apr 26, 2017 at 04:27:05PM +0530, Viresh Kumar wrote:
>>> Power-domains need to express their active states in DT and the devices
>>> within the power-domain need to express their dependency on those active
>>> states. The power-domains can use the OPP tables without any
>>> modifications to the bindings.
>>>
>>> Add a new property "power-domain-opp", which will contain phandle to the
>>> OPP node of the parent power domain. This is required for devices which
>>> have dependency on the configured active state of the power domain for
>>> their working.
>>>
>>> For some platforms the actual frequency and voltages of the power
>>> domains are managed by the firmware and are so hidden from the high
>>> level operating system. The "opp-hz" property is relaxed a bit to
>>> contain indexes instead of actual frequency values to support such
>>> platforms.
>>>
>>> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
>>> ---
>>>  Documentation/devicetree/bindings/opp/opp.txt | 74 ++++++++++++++++++++++++++-
>>>  1 file changed, 73 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/opp/opp.txt b/Documentation/devicetree/bindings/opp/opp.txt
>>> index 63725498bd20..6e30cae2a936 100644
>>> --- a/Documentation/devicetree/bindings/opp/opp.txt
>>> +++ b/Documentation/devicetree/bindings/opp/opp.txt
>>> @@ -77,7 +77,10 @@ This defines voltage-current-frequency combinations along with other related
>>>  properties.
>>>  
>>>  Required properties:
>>> -- opp-hz: Frequency in Hz, expressed as a 64-bit big-endian integer.
>>> +- opp-hz: Frequency in Hz, expressed as a 64-bit big-endian integer. In some
>>> +  cases the exact frequency in Hz may be hidden from the OS by the firmware and
>>> +  this field may contain values that represent the frequency in a firmware
>>> +  dependent way, for example an index of an array in the firmware.
>> 
>> Not really sure OPP binding makes sense here. What about all the other 
>> properties. We expose voltage, but not freq?
>> 
>
> I completely agree with that and I have been pushing this to be
> represented as just regulators[0]. Mark B seem to dislike that
> idea [1]

And Mark is right, because what's being described is not (simply) a
voltage regultor.  While it might be "just" voltage on some SoCs (for
now), it is clearly about performance (a.k.a. OPP) on others.

Kevin