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

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Message-ID: <cd147ab0-1304-a491-7a56-ee6199c02d32@gmail.com>
Date:   Thu, 5 Nov 2020 18:22:09 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     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

05.11.2020 12:45, Ulf Hansson пишет:
...
> I need some more time to review this, but just a quick check found a
> few potential issues...

Thank you for starting the review! I'm pretty sure it will take a couple
revisions until all the questions will be resolved :)

> The "core-supply", that you specify as a regulator for each
> controller's device node, is not the way we describe power domains.
> Instead, it seems like you should register a power-domain provider
> (with the help of genpd) and implement the ->set_performance_state()
> callback for it. Each device node should then be hooked up to this
> power-domain, rather than to a "core-supply". For DT bindings, please
> have a look at Documentation/devicetree/bindings/power/power-domain.yaml
> and Documentation/devicetree/bindings/power/power_domain.txt.
> 
> In regards to the "sync state" problem (preventing to change
> performance states until all consumers have been attached), this can
> then be managed by the genpd provider driver instead.

I'll need to take a closer look at GENPD, thank you for the suggestion.

Sounds like a software GENPD driver which manages clocks and voltages
could be a good idea, but it also could be an unnecessary
over-engineering. Let's see..