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

From: Viresh Kumar <viresh.kumar@linaro.org>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>,
	Rafael Wysocki <rjw@rjwysocki.net>,
	Kevin Hilman <khilman@linaro.org>,
	Viresh Kumar <vireshk@kernel.org>, Nishanth Menon <nm@ti.com>,
	Stephen Boyd <sboyd@codeaurora.org>,
	linaro-kernel <linaro-kernel@lists.linaro.org>,
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Rob Herring <robh+dt@kernel.org>,
	Lina Iyer <lina.iyer@linaro.org>,
	Rajendra Nayak <rnayak@codeaurora.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>
Subject: Re: [PATCH V4 1/9] PM / OPP: Allow OPP table to be used for power-domains
Date: Thu, 20 Apr 2017 15:03:01 +0530	[thread overview]
Message-ID: <20170420093301.GI5436@vireshk-i7> (raw)
In-Reply-To: <CAPDyKFq5xwv5Vy6wNfjFYi_4+immDH9UKTS1EG2j6c4OwnQONg@mail.gmail.com>

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