linux-kernel - Re: [PATCH V4 1/9] PM / OPP: Allow OPP table to be used for power-domains

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Message-ID: <CAPDyKFq5xwv5Vy6wNfjFYi_4+immDH9UKTS1EG2j6c4OwnQONg@mail.gmail.com>
Date:   Thu, 20 Apr 2017 10:23:03 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...aro.org>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        linaro-kernel <linaro-kernel@...ts.linaro.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Lina Iyer <lina.iyer@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH V4 1/9] PM / OPP: Allow OPP table to be used for power-domains

Viresh, Sudeep,

Sorry for jumping in late.

[...]

>> On the contrary(playing devil's advocate here), we can treat all
>> existing regulators alone as OPP then if you strip the voltages and
>> treat it as abstract number.
>
> But then we are going to have lots of platform specific code which
> will program the actual hardware, etc. Which is all handled by the
> regulator framework. Also note that the regulator core selects the
> common voltage selected by all the children, while we want to select
> the highest performance point here.

If I understand correctly, Sudeep is not convinced that this is about
PM domain regulator(s), right?

To me there is no doubt, these regulators is exactly the definition of
PM domain regulators.

That said, long time ago we have decided PM domain regulator shall be
modeled as exactly that. From DT point of view, this means the handle
to the PM domain regulator belongs in the node of the PM domain
controller - and not in each device's node of those belonging to the
PM domain.

Isn't that what this discussion really boils down to? Or maybe I am
not getting it.

>
> Even if we have to configure both clock and voltage for the power
> domain using standard clk/regulator frameworks, OPP will work just
> fine as it will do that then. So, its not that we are bypassing the
> regulator framework here. It will be used if we have the voltages
> available for the power-domain's performance states.
>
>> So if the firmware handles more than just
>> regulators, I agree.
>
> I don't know the internals of that really.
>
>> At the same time, I would have preferred firmware
>> to even abstract the frequency like ACPI CPPC.
>
> Frequency isn't required to be configured for the cases I know, but it
> can be in future implementations.

To me using OPP tables makes sense as it gives us the flexibility that
is needed. If I understand correct, that was also Kevin's point.

[...]

Kind regards
Uffe