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

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Ulf,

On Tue, Sep 27, 2022 at 11:49 AM Ulf Hansson <ulf.hansson@linaro.org> wrote:
> > >>>> 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. :-)

It's not that simple: being part of a PM Domain is not a property of the
device being described, but a property of the integration into the SoC.

All synchronous hardware needs power (single/multiple), clock(s), and
reset(s).  But the granularity of control over power(s), clocks, and resets
depends on the integration.  So the related properties can appear
anywhere.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds