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From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Mon, 22 Aug 2022 10:38:11 +0200
Message-ID: <CACRpkdZXTtar73-HP8_wcAsCYw7JOgPwkXZt-_3s0GdoggBABw@mail.gmail.com>
Subject: Re: [RFC PATCH 0/1] Making Rockchip IO domains dependency from other
 devices explicit
To:     Quentin Schulz <foss+kernel@0leil.net>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     heiko@sntech.de, linux-gpio@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-rockchip@lists.infradead.org, linux-kernel@vger.kernel.org,
        Quentin Schulz <quentin.schulz@theobroma-systems.com>
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On Tue, Aug 2, 2022 at 11:53 AM Quentin Schulz <foss+kernel@0leil.net> wrote:

> Some background on IO domains on Rockchip:
>
> On some Rockchip SoCs, some SoC pins are split in what are called IO
> domains.
>
> An IO domain is supplied power externally, by regulators from a PMIC for
> example. This external power supply is then used by the IO domain as
> "supply" for the IO pins if they are outputs.
>
> Each IO domain can configure which voltage the IO pins will be operating
> on (1.8V or 3.3V).
>
> There already exists an IO domain driver for Rockchip SoCs[1]. This
> driver allows to explicit the relationship between the external power
> supplies and IO domains[2]. This makes sure the regulators are enabled
> by the Linux kernel so the IO domains are supplied with power and
> correctly configured as per the supplied voltage.
> This driver is a regulator consumer and does not offer any other
> interface for device dependency.

What makes me confused about the patch is the relationship, if any,
between this "IO domain" and generic power domains (genpd) that has
been worked on for ~10 years.

I am worried that we are reinventing the world.

While my intuitive feeling is that genpd power domains are only on-chip
and not considering off-chip pins, I am not so sure that it warrants
its own abstraction and want to know whether this can be retrofit into
genpd rather than inventing this?

Documentation/devicetree/bindings/power/power-domain.yaml
include/linux/pm_domain.h

Yours,
Linus Walleij