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

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Date:   Fri, 13 Nov 2020 15:45:43 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        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, 12 Nov 2020 at 23:14, Dmitry Osipenko <digetx@...il.com> wrote:
>
> 12.11.2020 23:43, Thierry Reding пишет:
> >> The difference in comparison to using voltage regulator directly is
> >> minimal, basically the core-supply phandle is replaced is replaced with
> >> a power-domain phandle in a device tree.
> > These new power-domain handles would have to be added to devices that
> > potentially already have a power-domain handle, right? Isn't that going
> > to cause issues? I vaguely recall that we already have multiple power
> > domains for the XUSB controller and we have to jump through extra hoops
> > to make that work.
>
> I modeled the core PD as a parent of the PMC sub-domains, which
> presumably is a correct way to represent the domains topology.
>
> https://gist.github.com/digetx/dfd92c7f7e0aa6cef20403c4298088d7

That could make sense, it seems.

Anyway, this made me realize that
dev_pm_genpd_set_performance_state(dev) returns -EINVAL, in case the
device's genpd doesn't have the ->set_performance_state() assigned.
This may not be correct. Instead we should likely consider an empty
callback as okay and continue to walk the topology upwards to the
parent domain, etc.

Just wanted to point this out. I intend to post a patch as soon as I
can for this.

[...]

Kind regards
Uffe