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

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Message-ID: <CACRpkdb4qZSUNhEjRRJi=5H-GvBi_h-0BAfDHJct5SjLKZSc3g@mail.gmail.com>
Date:   Mon, 18 Jul 2022 11:49:11 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Max Krummenacher <max.oss.09@...il.com>,
        Max Krummenacher <max.krummenacher@...adex.com>,
        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>,
        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>,
        "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

On Wed, Jul 13, 2022 at 1:44 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:

> > > 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.
>
> This isn't entirely correct. The callbacks of a genpd, *may* execute
> in atomic context, but that depends on whether the GENPD_FLAG_IRQ_SAFE
> is set for it or not.
>
> Similar to what we have for runtime PM callbacks, with pm_runtime_irq_safe().

Aha I stand corrected!

> > > 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.)
>
> Yep, unfortunately I never got to the point. However, poking the
> registers directly from the genpd provider's on/off callbacks has
> never been my plan.
>
> Instead I would rather expect us to call into a Ux500 specific
> interface for the prcmu FW. Simply because it's not really a regulator
> and must not be modelled like it. Instead it is a voltage/frequency
> domain that is managed behind a FW interface.

We should take a stab at this, PostmarketOS just added support
for three more U8500 phones so they support all the Samsung models
and we have actual users of these systems. I think this would save
them quite a lot of power. Also I use these targets for a lot of
misc testing (like Kasan etc).

Yours,
Linus Walleij