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

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Date:   Thu, 28 Jul 2022 13:21:46 +0200
From:   Francesco Dolcini <francesco.dolcini@...adex.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Robin Murphy <robin.murphy@....com>
Cc:     Francesco Dolcini <francesco.dolcini@...adex.com>,
        Max Krummenacher <max.oss.09@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Max Krummenacher <max.krummenacher@...adex.com>,
        Linux PM list <linux-pm@...r.kernel.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>,
        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 Thu, Jul 28, 2022 at 11:37:07AM +0200, Ulf Hansson wrote:
> On Tue, 26 Jul 2022 at 18:03, Francesco Dolcini
> <francesco.dolcini@...adex.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@...il.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.

Francesco