Re: [PATCH v1 00/30] Introduce core voltage scaling for NVIDIA Tegra20/30 SoCs

From: Ulf Hansson <ulf.hansson@linaro.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Dmitry Osipenko" <digetx@gmail.com>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Jonathan Hunter" <jonathanh@nvidia.com>,
	"Alan Stern" <stern@rowland.harvard.edu>,
	"Peter Chen" <Peter.Chen@nxp.com>,
	"Mark Brown" <broonie@kernel.org>,
	"Liam Girdwood" <lgirdwood@gmail.com>,
	"Adrian Hunter" <adrian.hunter@intel.com>,
	"Krzysztof Kozlowski" <krzk@kernel.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Lee Jones" <lee.jones@linaro.org>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Marek Szyprowski" <m.szyprowski@samsung.com>,
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Subject: Re: [PATCH v1 00/30] Introduce core voltage scaling for NVIDIA Tegra20/30 SoCs
Date: Thu, 5 Nov 2020 11:56:37 +0100	[thread overview]
Message-ID: <CAPDyKFpQG98d6foc1U6fp3YEBdZ1vLqY9cmWxpUwXoKgDn+ojQ@mail.gmail.com> (raw)
In-Reply-To: <20201105104009.oo4dc6a2gdcwduhk@vireshk-i7>

On Thu, 5 Nov 2020 at 11:40, Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> On 05-11-20, 11:34, Ulf Hansson wrote:
> > I am not objecting about scaling the voltage through a regulator,
> > that's fine to me. However, encoding a power domain as a regulator
> > (even if it may seem like a regulator) isn't. Well, unless Mark Brown
> > has changed his mind about this.
> >
> > In this case, it seems like the regulator supply belongs in the
> > description of the power domain provider.
>
> Okay, I wasn't sure if it is a power domain or a regulator here. Btw,
> how do we identify if it is a power domain or a regulator ?

Good question. It's not a crystal clear line in between them, I think.

A power domain to me, means that some part of a silicon (a group of
controllers or just a single piece, for example) needs some kind of
resource (typically a power rail) to be enabled to be functional, to
start with. If there are operating points involved, that's also a
clear indication to me, that it's not a regular regulator.

Maybe we should try to specify this more exactly in some
documentation, somewhere.

>
> > > In case of Qcom earlier (when we added the performance-state stuff),
> > > the eventual hardware was out of kernel's control and we didn't wanted
> > > (allowed) to model it as a virtual regulator just to pass the votes to
> > > the RPM. And so we did what we did.
> > >
> > > But if the hardware (where the voltage is required to be changed) is
> > > indeed a regulator and is modeled as one, then what Dmitry has done
> > > looks okay. i.e. add a supply in the device's node and microvolt
> > > property in the DT entries.
> >
> > I guess I haven't paid enough attention how power domain regulators
> > are being described then. I was under the impression that the CPUfreq
> > case was a bit specific - and we had legacy bindings to stick with.
> >
> > Can you point me to some other existing examples of where power domain
> > regulators are specified as a regulator in each device's node?
>
> No, I thought it is a regulator here and not a power domain.

Okay, thanks!

Kind regards
Uffe