linux-kernel - Re: [PATCH v1 0/5] power: domain: Add driver for a PM domain provider which controls

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Date:   Tue, 14 Jun 2022 09:22:10 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Max Krummenacher <max.oss.09@...il.com>,
        Max Krummenacher <max.krummenacher@...adex.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        Mark Brown <broonie@...nel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Andrejs Cainikovs <andrejs.cainikovs@...adex.com>,
        Biju Das <biju.das.jz@...renesas.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Fabio Estevam <festevam@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>, Vinod Koul <vkoul@...nel.org>,
        Will Deacon <will@...nel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 0/5] power: domain: Add driver for a PM domain provider
 which controls

Hi Rob,

On Mon, Jun 13, 2022 at 9:15 PM Rob Herring <robh@...nel.org> wrote:
> On Thu, Jun 09, 2022 at 05:08:46PM +0200, Max Krummenacher wrote:
> > From: Max Krummenacher <max.krummenacher@...adex.com>
> >
> > its power enable by using a regulator.
> >
> > The currently implemented PM domain providers are all specific to
> > a particular system on chip.
>
> Yes, power domains tend to be specific to an SoC... 'power-domains' is
> supposed to be power islands in a chip. Linux 'PM domains' can be
> anything...

> > This allows to use the "regulator-pm-pd" driver with an arbitrary
> > device just by adding the 'power-domains' property to the devices
> > device tree node. However the device's dt-bindings schema likely does
> > not allow the property 'power-domains'.
> > One way to solve this would be to allow 'power-domains' globally
> > similarly how 'status' and other common properties are allowed as
> > implicit properties.
>
> No. For 'power-domains' bindings have to define how many there are and
> what each one is.

IMO "power-domains" are an integration feature, i.e. orthogonal to the
actual device that is part of the domain.  Hence the "power-domains"
property may appear everywhere.

It is actually the same for on-chip devices, as an IP core may be
reused on a new SoC that does have power or clock domains.  For
these, we managed to handle that fine because most devices do have
some form of family- or SoC-specific compatible values to control if
the power-domains property can be present/is required or not.

But for off-chip devices, the integrator (board designed) can do
whatever he wants.  Off-chip devices do have the advantage that it
is usually well documented which power supply (if there are multiple)
serves which purpose, which is not always clear for on-chip devices.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds