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Date:   Thu, 5 Nov 2020 16:43:01 +0530
From:   Viresh Kumar <viresh.kumar@linaro.org>
To:     Ulf Hansson <ulf.hansson@linaro.org>
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Subject: Re: [PATCH v1 00/30] Introduce core voltage scaling for NVIDIA
 Tegra20/30 SoCs
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On 05-11-20, 11:56, Ulf Hansson wrote:
> On Thu, 5 Nov 2020 at 11:40, Viresh Kumar <viresh.kumar@linaro.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