Re: [PATCH 1/3] dt-bindings: pinctrl: Add bindings for mscc,ocelot-sgpio

[Linus Walleij]

On Wed, May 13, 2020 at 4:11 PM Lars Povlsen <lars.povlsen@xxxxxxxxxxxxx> wrote:

> This adds DT bindings for the Microsemi SGPIO controller, bindings
> mscc,ocelot-sgpio and mscc,luton-sgpio.
>
> Reviewed-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
> Signed-off-by: Lars Povlsen <lars.povlsen@xxxxxxxxxxxxx>

> +  microchip,sgpio-ports:
> +    description: This is a 32-bit bitmask, configuring whether a
> +      particular port in the controller is enabled or not. This allows
> +      unused ports to be removed from the bitstream and reduce latency.
> +    $ref: "/schemas/types.yaml#/definitions/uint32"

I don't know about this.

You are saying this pin controller can have up to 32 GPIO "ports"
(also known as banks).

Why can't you just represent each such port as a separate GPIO
node:

pinctrl@nnn {
    gpio@0 {
        ....
    };
    gpio@1 {
        ....
    };
    ....
    gpio@31 {
        ....
    };
};

Then if some of them are unused just set it to status = "disabled";

This also makes your Linux driver simpler because each GPIO port
just becomes a set of 32bit registers and you can use
select GPIO_GENERIC and bgpio_init() and save a whole
slew of standard stock code.

Yours,
Linus Walleij