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

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Date:   Thu, 20 Apr 2017 15:03:01 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        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

On 20-04-17, 10:23, Ulf Hansson wrote:
> 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.

Maybe not. I think Sudeep understands that this is about PM domain
regulators only but he is asking why aren't we solving this problem
using regulators framework but performance-levels instead.

> >
> > 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.

Right.

-- 
viresh