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From:   Ulf Hansson <ulf.hansson@linaro.org>
Date:   Fri, 26 Aug 2022 15:50:46 +0200
Message-ID: <CAPDyKFqtCxrjALeCmhuqQ2VmmUHhi-DjXO30uHChTPFeDbp+JQ@mail.gmail.com>
Subject: Re: [PATCH v1 0/5] power: domain: Add driver for a PM domain provider
 which controls
To:     Francesco Dolcini <francesco.dolcini@toradex.com>
Cc:     Mark Brown <broonie@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Max Krummenacher <max.oss.09@gmail.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Max Krummenacher <max.krummenacher@toradex.com>,
        Linux PM list <linux-pm@vger.kernel.org>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        Kevin Hilman <khilman@kernel.org>,
        Andrejs Cainikovs <andrejs.cainikovs@toradex.com>,
        Biju Das <biju.das.jz@bp.renesas.com>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Fabio Estevam <festevam@gmail.com>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Marcel Ziswiler <marcel.ziswiler@toradex.com>,
        NXP Linux Team <linux-imx@nxp.com>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Rob Herring <robh+dt@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Shawn Guo <shawnguo@kernel.org>, Vinod Koul <vkoul@kernel.org>,
        Will Deacon <will@kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
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On Thu, 28 Jul 2022 at 13:21, Francesco Dolcini
<francesco.dolcini@toradex.com> wrote:
>
> On Thu, Jul 28, 2022 at 11:37:07AM +0200, Ulf Hansson wrote:
> > On Tue, 26 Jul 2022 at 18:03, Francesco Dolcini
> > <francesco.dolcini@toradex.com> wrote:
> > >
> > > Hello Ulf and everybody,
> > >
> > > On Wed, Jul 13, 2022 at 01:43:28PM +0200, Ulf Hansson wrote:
> > > > On Thu, 23 Jun 2022 at 18:14, Max Krummenacher <max.oss.09@gmail.com> wrote:
> > > > > So our plan is to explicitly handle a (shared) regulator in every
> > > > > driver involved, adding that regulator capability for drivers not
> > > > > already having one.
> > > >
> > > > Please don't! I have recently rejected a similar approach for Tegra
> > > > platforms, which now have been converted into using the power domain
> > > > approach.
> > >
> > > Just to quickly re-iterate how our hardware design looks like, we do
> > > have a single gpio that control the power of a whole board area that is
> > > supposed to be powered-off in suspend mode, this area could contains
> > > devices that have a proper Linux driver and some passive driver-less
> > > components (e.g. level shifter) - the exact mix varies.
> > >
> > > Our proposal in this series was to model this as a power domain that
> > > could be controlled with a regulator. Krzysztof, Robin and others
> > > clearly argued against this idea.
> >
> > Well, historically we haven't modelled these kinds of power-rails
> > other than through power-domains. And this is exactly what genpd and
> > PM domains in Linux are there to help us with.
> >
> > Moreover, on another SoC/platform, maybe the power-rails are deployed
> > differently and maybe those have the ability to scale performance too.
> > Then it doesn't really fit well with the regulator model anymore.
> >
> > If we want to continue to keep drivers portable, I don't see any
> > better option than continuing to model these power-rails as
> > power-domains.
> >
> > >
> > > The other approach would be to have a single regulator shared with the
> > > multiple devices we have there (still not clear how that would work in
> > > case we have only driver-less passive components). This is just a
> > > device-tree matter, maybe we would need to add support for a supply to
> > > some device drivers.
> > >
> > > Honestly my conclusion from this discussion is that the only viable
> > > option is this second one, do I miss something?
> >
> > No thanks!
> >
> > Well, unless you can convince me there are benefits to this approach
> > over the power-domain approach.
>
> I'm fine with our current power-domain proposal here, I do not need to
> convince you, I have the other problem to convince someone to merge
> it :-)
>
> Maybe Krzysztof, Robin or Mark can comment again after you explained
> your view on this topic.

To move things forward, I suggest you re-start with the power domain approach.

Moreover, to avoid any churns, just implement it as another new SoC
specific genpd provider and let the provider deal with the regulator.
In this way, you don't need to invent any new types of DT bindings,
but can re-use existing ones.

If you post a new version, please keep me cced, then I will help to review it.

Kind regards
Uffe