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

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Message-ID: <CAPDyKFrDFAif3DnvPoLrgJ2+fv+aB9GyOoG_O3q-1m=2Y5eT5w@mail.gmail.com>
Date:   Tue, 27 Sep 2022 11:48:48 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Francesco Dolcini <francesco.dolcini@...adex.com>,
        Mark Brown <broonie@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Robin Murphy <robin.murphy@....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

[...]

> >>>>
> >>>> The main concern that was raised on this topic was that we have to
> >>>> somehow link the power-domain to the specific peripherals (the power
> >>>> domain consumer) in the device tree.
> >>>
> >>> Yes, that is needed. Although, I don't see how that is a concern?
> >>>
> >>> We already have the valid bindings to use for this, see more below.
> >>>
> >>>>
> >>>> Adding the power-domain property there will trigger validation errors
> >>>> unless we do explicitly add the power-domains to the schema for each
> >>>> peripheral we need this. To me this does not really work, but maybe I'm
> >>>> not understanding something.
> >>>>
> >>>> This is what Rob wrote on the topic [1]:
> >>>>   > No. For 'power-domains' bindings have to define how many there are and
> >>>>   > what each one is.
> >>>>
> >>>> Just as an example from patch [2]:
> >>>>
> >>>>   can1: can@0 {
> >>>>     compatible = "microchip,mcp251xfd";
> >>>>     power-domains = <&pd_sleep_moci>;
> >>>>   };
> >>>>
> >>>> leads to:
> >>>>
> >>>>   imx8mm-verdin-nonwifi-dahlia.dtb: can@0: 'power-domains' does not match any of the regexes: 'pinctrl-[0-9]+'
> >>>>           From schema: .../bindings/net/can/microchip,mcp251xfd.yaml
> >>>
> >>> I think it should be fine to just add the below line to the DT
> >>> bindings, for each peripheral device to fix the above problem.
> >>>
> >>> power-domains: true
> >>
> >> Again, as Rob said, no, because it must be strictly defined. So for
> >> example: "maxItems: 1" for simple cases. But what if device is then part
> >> of two power domains?
> >>
> >>>
> >>> That should be okay, right?
> >>
> >> Adding it to each peripheral scales poorly. Especially that literally
> >> any device can be part of such power domain.
> >
> > Right.
> >
> >>
> >> If we are going with power domain approach, then it should be applicable
> >> basically to every device or to every device of some class (e.g. I2C,
> >> SPI). This means it should be added to respective core schema in
> >> dtschema repo, in a way it does not interfere with other power-domains
> >> properties (existing ones).
> >
> > Isn't that already taken care of [1]?
>
> No, because it does not define the items (what are the power domains and
> how many). This binding expects that any device has maxItems restricting it.

Right, apologize for my ignorance.

>
> >
> > If there is more than one power domain per device, perhaps we may need
> > to extend it with a more strict binding? But, that doesn't seem to be
> > the case here - and if it turns out to be needed later on, we can
> > always extend the bindings, no?
> >
> > Note also that we already have DT bindings specifying "power-domains:
> > true" to deal with the above. Isn't that what we want?
>
> You mentioned it before and both me and Rob already responded - no,
> because it does not restrict the number of items.

Okay, so maxItems need to be specified for each peripheral. It's not a
big deal, right?

Of course, it would be even easier if the core schema would use a
default "maxItems: 1" for power domain consumers, which of course must
be possible to be overridden for those consumers that need something
else. But perhaps it's not that simple. :-)

Kind regards
Uffe