Re: [PATCH v2 3/4] pinctrl: mcp23s08: work around GPIO line naming

["Jan Kundrát" <jan.kundrat@cesnet.cz>]

On čtvrtek 7. března 2019 22:35:15 CET, Thomas Petazzoni wrote:
> Hello Jan,
>
> On Thu, 7 Mar 2019 14:31:02 +0100
> Jan Kundrát <jan.kundrat@cesnet.cz> wrote:
>
>> +Line naming
>> +===========
>> +
>> +Because several gpio_chip instances are hidden below a single device tree
>
> Mentioning a Linux specific data structure (gpio_chip here) in a Device
> Tree binding documentation does not seem like a good idea. Bindings are
> supposed to be OS-agnostic.

Hi Thomas, that's a fair comment. On the other hand, this driver's DT 
bindings are already quite Linux specific with their 
"microchip,spi-present-mask" workaround. The way I understand this, Linux 
does not support multiple child devices "within" one SPI slave. If there 
was proper support for this, this patch would be superfluous.

I, too, would love to see this driver changed so that the bindings look, 
e.g., like this:

  gpio_spi_chips: gpio@1 {
    compatible = "microchip,mcp23s17-multiple";

    gpio-bank@1 {
      compatible = "microchip,mcp23s17";
      reg = <1>;
      interrupt-parent = <&gpio1>;
      interrupts = <22 IRQ_TYPE_LEVEL_LOW>;
      interrupt-controller;
      #interrupt-cells = <2>;
      gpio-controller;
      #gpio-cells = <2>;
      microchip,irq-mirror;
      drive-open-drain;
      spi-max-frequency = <10000000>;
      gpio-line-names =
        "foo",
        //...
        ;
       random_pin {
         gpio-hog;
         gpios = <6 GPIO_ACTIVE_HIGH>;
         input;
         line-name = "this hogs just one pin";
       };
    };

    gpio-bank@2 {
      compatible = "microchip,mcp23s17";
      reg = <2>;
      interrupt-parent = <&gpio1>;
      interrupts = <22 IRQ_TYPE_LEVEL_LOW>;
      interrupt-controller;
      #interrupt-cells = <2>;
      gpio-controller;
      #gpio-cells = <2>;
      microchip,irq-mirror;
      drive-open-drain;
      spi-max-frequency = <10000000>;
      gpio-line-names =
        "bar",
        //...
        ;
    };

However, I am not volunteering to do this work -- that's quite out of my 
league and available time.

With kind regards,
Jan