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

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Date:   Thu, 5 Nov 2020 16:43:01 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ulf Hansson <ulf.hansson@...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 05-11-20, 11:56, Ulf Hansson wrote:
> On Thu, 5 Nov 2020 at 11:40, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > Btw, how do we identify if it is a power domain or a regulator ?

To be honest, I was a bit afraid and embarrassed to ask this question,
and was hoping people to make fun of me in return :)

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

And I was relieved after reading this :)

> 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.

Isn't this what a part of regulator does as well ? i.e.
enabling/disabling of the regulator or power to a group of
controllers.

Over that the regulator does voltage/current scaling as well, which
normally the power domains don't do (though we did that in
performance-state case).

> If there are operating points involved, that's also a
> clear indication to me, that it's not a regular regulator.

Is there any example of that? I hope by OPP you meant both freq and
voltage here. I am not sure if I know of a case where a power domain
handles both of them.

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

I think yes, it is very much required. And in absence of that I think,
many (or most) of the platforms that also need to scale the voltage
would have modeled their hardware as a regulator and not a PM domain.

What I always thought was:

- Module that can just enable/disable power to a block of SoC is a
  power domain.

- Module that can enable/disable as well as scale voltage is a
  regulator.

And so I thought that this patchset has done the right thing. This
changed a bit with the qcom stuff where the IP to be configured was in
control of RPM and not Linux and so we couldn't add it as a regulator.
If it was controlled by Linux, it would have been a regulator in
kernel for sure :)

-- 
viresh