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

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Date:   Thu, 16 Jun 2022 14:50:49 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Max Krummenacher <max.oss.09@...il.com>
Cc:     max.krummenacher@...adex.com, Ulf Hansson <ulf.hansson@...aro.org>,
        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>,
        Rob Herring <robh+dt@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>, Vinod Koul <vkoul@...nel.org>,
        Will Deacon <will@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 0/5] power: domain: Add driver for a PM domain provider
 which controls

On Thu, Jun 9, 2022 at 5:10 PM Max Krummenacher <max.oss.09@...il.com> wrote:

> This series adds a PM domain provider driver which enables/disables
> a regulator to control its power state.

Actually, we did this on the U8500 in 2011.

IIRC this led to problems because we had to invent "atomic regulators"
because regulators use kernel abstractions that assume slowpath
(process context) and power domains does not, i.e. they execute in
fastpath, such as an interrupt handler.

The atomic regulator was a subset of regulator that only handled
regulators that would result in something like an atomic register write.

In the end it was not worth trying to upstream this approach, and
as I remember it, Ulf Hansson intended to let the power domains poke
these registers directly, which was easier. (It's on Ulfs TODO list to
actually implement this, hehe.)

Yours,
Linus Walleij