Re: [PATCH v1 1/1] pinctrl: add pinctrl/GPIO driver for Apple SoCs

[Linus Walleij <linus.walleij@linaro.org>]

On Sun, Sep 26, 2021 at 2:56 PM Sven Peter <sven@svenpeter.dev> wrote:
> On Sun, Sep 26, 2021, at 14:48, Linus Walleij wrote:

> > I think npins should be known from the compatible (we know that
> > this version of the SoC has so and so many pins) and the base
> > should always be 0? It's not like we have several pin controllers
> > of this type in the SoC is it?
>
> I've just checked: Looks like there are four different pin controllers of
> this type with a different number of pins each in Apple's device tree for
> the M1.

So we need to understand this hardware: is this something like
south/north/east/west, so the pins are oriented around the chip?

I would suspect they should then be compatibles:
apple,t8103-pinctrl-north, apple,t8103-pinctrl
apple,t8103-pinctrl-south, apple,t8103-pinctrl
apple,t8103-pinctrl-west, apple,t8103-pinctrl
apple,t8103-pinctrl-east, apple,t8103-pinctrl

going from specific to general signifying that we know which one
we are dealing with and then we know the npins etc.

This also gives a normal grouping of functions associated with
pins and the portion of the SoC, see for
example drivers/pinctrl/intel/pinctrl-broxton.c.

This shows that it might have been a bad idea to define the
pins as opaque, because now that is hiding the fact that
these pins are grouped in four distinct sets.
APPLE_PINMUX(pin, func)

Should rather have been APPLE_PINMUX(cardinal, pin, func)
where cardinal would be 0..3 for north, south, west, east.

This is a bit of guessing actually, but we should definitely
try to make the driver reflect the reality and not over-generalize.
If these four blocks in the SoC are different, they should have
different compatible strings, because they are not, by
definition, compatible.

Yours,
Linus Walleij