Re: [PATCH V2 1/6] dt-bindings: pinctrl: support specifying pins, groups & functions

[Rafał Miłecki <zajec5@xxxxxxxxx>]

On 25.11.2021 09:49, Tony Lindgren wrote:
> * Rafał Miłecki <zajec5@xxxxxxxxx> [211124 23:05]:
> > --- a/Documentation/devicetree/bindings/pinctrl/pinctrl.yaml
> > +++ b/Documentation/devicetree/bindings/pinctrl/pinctrl.yaml
> > @@ -42,4 +42,44 @@ properties:
> >         This property can be set either globally for the pin controller or in
> >         child nodes for individual pin group control.
> >   
> > +  pins:
> > +    type: object
> > +
> > +    patternProperties:
> > +      "^.*$":
> > +        type: object
> > +
> > +        properties:
> > +          number:
> > +            description: Pin number
> > +            $ref: /schemas/types.yaml#/definitions/uint32
> > +
> > +        additionalProperties: false
>
> Please don't introduce Linux kernel internal numbering here. It's
> like bringing back the interrupt numbers again.

This is a new bit to me and the reason why I got this binding that way.

I had no idea pin numbering is system specific thing. I always thought
pin numbers are present in every chip datasheets and that is just a part
of hardware.

Now I'm reading https://www.kernel.org/doc/Documentation/pinctrl.txt
again it indeed seems to mention that numbering is handled in a way not
related to specs: "I enumerated the pins from 0 in the upper left corner
to 63 in the lower right corner.".

Sorry for that, I hopefully understand your point correctly now.


> Just make this into
> a proper hardware offset from the controller base, so a reg property.
> Sure in some cases the reg property is just an index depending on
> the controller, we don't really care from the binding point of view.
>
> We already have #pinctrl-cells, so plase do something like the four
> ximaginary examples below:
>
> 	#pinctrl-cells = <1>;
> 	...
> 	pin@foo {
> 		reg = <0xf00 MUX_MODE0>;
> 		label = "foo_pin";
> 	};
>
>
> 	#pinctrl-cells = <2>;
> 	...
> 	pin@foo {
> 		reg = <0xf00 PIN_INPUT_PULLUP MUX_MODE3>;
> 	};
>
>
> 	#pinctrl-cells = <2>;
> 	...
> 	pin@f00 {
> 		reg = <0xf00 DELAY_PS(0) DELAY_PS(0)>;
> 	};
>
>
> 	#pinctrl-cells = <3>;
> 	...
> 	pin@f00 {
> 		reg = <0xf00 MUX_MODE3 PULL_UP_STRENGTH(36) PULL_DOWN_STRENGTH(20)>;
> 	};
>
>
> Then let's attempt to use just standard numbers and defines for the
> values where possible. Then a group of pins is just a list of the pin
> phandles in the devicetree.

I need to ask for help on understanding that reg = <...> syntax.

(Why) do we need to put that extra info in a "reg" property? That seems
like either:
1. Pin specific info
or
2. Phandle arguments

In the first case, instead of:
	pin@f00 {
		reg = <0xf00 MUX_MODE3 PULL_UP_STRENGTH(36) PULL_DOWN_STRENGTH(20)>;
	};
I'd rather use:
	pin@f00 {
		reg = <0xf00>;
		mux_mode3;
		pull_up_strength = <36>;
		pull_down_strength = <20>;
	};

In the second case, shouldn't that be something like:
	pins {
		bar: pin@f00 {
			reg = <0xf00>;
			#pinctrl-cells = <3>;
		};
	};

	groups {
		qux {
			pins = <&bar MUX_MODE3 PULL_UP_STRENGTH(36) PULL_DOWN_STRENGTH(20)>;
		}
	};