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

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Message-ID: <CAPDyKFoCJt5MBSKBJ8n1OAMdVsWHdwXTx0zFEcZw_F_gQ6Ug0w@mail.gmail.com>
Date:   Thu, 5 Nov 2020 11:34:26 +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 11:06, Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 05-11-20, 10:45, Ulf Hansson wrote:
> > + Viresh
>
> Thanks Ulf. I found a bug in OPP core because you cc'd me here :)

Happy to help. :-)

>
> > On Thu, 5 Nov 2020 at 00:44, Dmitry Osipenko <digetx@...il.com> wrote:
> > I need some more time to review this, but just a quick check found a
> > few potential issues...
> >
> > The "core-supply", that you specify as a regulator for each
> > controller's device node, is not the way we describe power domains.
>
> Maybe I misunderstood your comment here, but there are two ways of
> scaling the voltage of a device depending on if it is a regulator (and
> can be modeled as one in the kernel) or a power domain.

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.

>
> 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?

Kind regards
Uffe