Re: [PATCH] gpio: Document the 'valid_mask' being internal

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Thu, Feb 27, 2025 at 9:24 AM Matti Vaittinen
<mazziesaccount@xxxxxxxxx> wrote:

> I did some quick testing. I used:
(...)
> which left GPIO0 ... GPIO6 masked (pins used for ADC) and only GPIO7
> unmasked.
>
> Then I added:
> gpiotst {
>         compatible = "rohm,foo-bd72720-gpio";
>         rohm,dvs-vsel-gpios = <&adc 5 0>, <&adc 6 0>;
> };
>
> and a dummy driver which does:
> gpio_array = devm_gpiod_get_array(&pdev->dev, "rohm,dvs-vsel",
>                                   GPIOD_OUT_LOW);
>
> ...
>
> ret = gpiod_set_array_value_cansleep(gpio_array->ndescs,
>                 gpio_array->desc, gpio_array->info, values);
>
> As a result the bd79124 gpio driver got it's set_multiple called with
> masked pins. (Oh, and I had accidentally prepared to handle this as I
> had added a sanity check for pinmux register in the set_multiple()).

But... how did you mask of the pins 0..5 in valid_mask in this
example?

If this is device tree, I would expect that at least you set up
gpio-reserved-ranges = <0 5>; which will initialize the valid_mask.

You still need to tell the gpiolib that they are taken for other
purposes somehow.

I think devm_gpiod_get_array() should have failed in that case.

The call graph should look like this:

devm_gpiod_get_array()
    gpiod_get_array()
        gpiod_get_index(0...n)
            gpiod_find_and_request()
                gpiod_request()
                    gpiod_request_commit()
                        gpiochip_line_is_valid()

And gpiochip_line_is_valid() looks like this:

bool gpiochip_line_is_valid(const struct gpio_chip *gc,
                unsigned int offset)
{
    /* No mask means all valid */
    if (likely(!gc->valid_mask))
        return true;
    return test_bit(offset, gc->valid_mask);
}

So why is this not working?

Yours,
Linus Walleij