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

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Message-ID: <CAPDyKFpQG98d6foc1U6fp3YEBdZ1vLqY9cmWxpUwXoKgDn+ojQ@mail.gmail.com>
Date:   Thu, 5 Nov 2020 11:56:37 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Peter Chen <Peter.Chen@....com>,
        Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Lee Jones <lee.jones@...aro.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Peter Geis <pgwipeout@...il.com>,
        Nicolas Chauvet <kwizart@...il.com>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        driverdevel <devel@...verdev.osuosl.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        linux-pwm@...r.kernel.org,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v1 00/30] Introduce core voltage scaling for NVIDIA
 Tegra20/30 SoCs

On Thu, 5 Nov 2020 at 11:40, Viresh Kumar <viresh.kumar@...aro.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