linux-kernel - Re: [PATCH] gpio: Document the 'valid

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Message-ID: <CACRpkdafJfmuO++XXSFha51Q5=9DrqqRtxOpNeUsmvy7BHrC2g@mail.gmail.com>
Date: Fri, 28 Feb 2025 09:23:19 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Matti Vaittinen <mazziesaccount@...il.com>
Cc: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>, Bartosz Golaszewski <brgl@...ev.pl>, 
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpio: Document the 'valid_mask' being internal

On Thu, Feb 27, 2025 at 9:24 AM Matti Vaittinen
<mazziesaccount@...il.com> 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