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

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Date:   Wed, 15 Jun 2022 17:31:01 +0000
From:   Marcel Ziswiler <marcel.ziswiler@...adex.com>
To:     "max.oss.09@...il.com" <max.oss.09@...il.com>,
        "krzysztof.kozlowski@...aro.org" <krzysztof.kozlowski@...aro.org>,
        "geert@...ux-m68k.org" <geert@...ux-m68k.org>
CC:     "linux-imx@....com" <linux-imx@....com>,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        "robh@...nel.org" <robh@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
        "biju.das.jz@...renesas.com" <biju.das.jz@...renesas.com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "geert+renesas@...der.be" <geert+renesas@...der.be>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "khilman@...nel.org" <khilman@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        Andrejs Cainikovs <andrejs.cainikovs@...adex.com>,
        "will@...nel.org" <will@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "festevam@...il.com" <festevam@...il.com>,
        Max Krummenacher <max.krummenacher@...adex.com>,
        "broonie@...nel.org" <broonie@...nel.org>
Subject: Re: [PATCH v1 0/5] power: domain: Add driver for a PM domain provider
 which controls

Hi

On Wed, 2022-06-15 at 10:15 -0700, Krzysztof Kozlowski wrote:
> On 15/06/2022 09:10, Max Krummenacher wrote:
> > Hi
> > 
> > On Tue, Jun 14, 2022 at 9:22 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > 
> > > Hi Rob,
> > > 
> > > On Mon, Jun 13, 2022 at 9:15 PM Rob Herring <robh@...nel.org> wrote:
> > > > On Thu, Jun 09, 2022 at 05:08:46PM +0200, Max Krummenacher wrote:
> > > > > From: Max Krummenacher <max.krummenacher@...adex.com>
> > > > > 
> > > > > its power enable by using a regulator.
> > > > > 
> > > > > The currently implemented PM domain providers are all specific to
> > > > > a particular system on chip.
> > > > 
> > > > Yes, power domains tend to be specific to an SoC... 'power-domains' is
> > > > supposed to be power islands in a chip. Linux 'PM domains' can be
> > > > anything...
> > 
> > I don't see why such power islands should be restricted to a SoC. You can
> > build the exact same idea on a PCB or even more modular designs.
> 
> In the SoC these power islands are more-or-less defined. These are real
> regions gated by some control knob.
> 
> Calling few devices on a board "power domain" does not make it a power
> domain. There is no grouping, there is no control knob.
> 
> Aren't you now re-implementing regulator supplies? How is this different
> than existing supplies?

I believe the biggest difference between power-domains and regulator-supplies lays in the former being driver
agnostic while the later is driver specific. Meaning with power-domains one can just add such arbitrary
structure to the device tree without any further driver specific changes/handling required. While with
regulator-supplies each and every driver actually needs to have driver specific handling thereof added. Or do I
miss anything?

We are really trying to model something where a single GPIO pin (via a GPIO regulator or whatever) can control
power to a variety of on-board peripherals. And, of course, we envision runtime PM actually making use of it
e.g. when doing suspend/resume.

> Best regards,
> Krzysztof

Cheers

Marcel