Re: [PATCH 2/3] pinctrl: zx: Add ZTE pinctrl dts document

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Tue, Sep 6, 2016 at 4:15 PM, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:

> pa: pinctrla {
>     compatible = "parent-device-compat";
>     (...)
> };
>
> pb: pinctrlb {
>     compatible = "child-device-compat";
>     pinctrl-parent = &pinctrla;
>     (...)
> };

After thinking some more I kind of fancy the GPIO ranges
approach to be reused:

pa: pinctrla {
    compatible = "parent-device-compat";
    (...)
};

pb: pinctrlb {
    compatible = "child-device-compat";
    pinctrl-ranges = <&pa 0 31 0>;
    (...)
};

The definition and use would be similar to gpio-ranges, see:
Documentation/devicetree/bindings/gpio/gpio.txt, but these
bindings are specified in BNF which IMO is just confusing.

Anyways its <phandle local-offset count remote-offset>

Also group names are supported for GPIO ranges.

In the Linux implementation this facilitates reuse of the
existing GPIO ranges parsing and resolution.

To make cross-calls we need an abstract call akin to the
existing pinctrl_request_gpio() and pinctrl_free_gpio()
just named pinctrl_request_hierarchical()
pinctrl_free_hierarchical() or so so it is chrystal clear
what is going on when reading the code.

As this passes through the pinctrl driver core, new callbacks
are needed in struct pinmux_ops such as
.hierarchical_request(), .hierarchical_free().

This is going to be complex, but a way more maintainable
solution than doing the hack in patch 1/3 where we totally
loose control and definition of what happens.

Yours,
Linus Walleij
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