linux-kernel - Re: [PATCH] gpiolib: of: fix bounds check for valid mask

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Date:   Mon, 11 Apr 2022 19:55:43 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Andrei Lalaev <andrei.lalaev@...id.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: of: fix bounds check for valid mask

On Mon, Apr 11, 2022 at 5:46 PM Andrei Lalaev <andrei.lalaev@...id.com> wrote:

...

> > What does documentation tell about it?
>
> Documentation (devicetree/bindings/gpio/gpio.txt line 152) tells that
> "This property indicates the start and size of the GPIOs that can't be used."
> And the example (line 178) at the same file shows that the second element of
> a tuple is the count: "gpio-reserved-ranges = <0 4>, <12 2>;"
>
> > Does it need to be fixed?

This question was related to the documentation contents.

> I think so, because the current implementation doesn't reserve some GPIO ranges.
> For example, we have 20 GPIOs and we want to reserve GPIOs from 14 to 19.
> In this case the "reserved-ranges" looks like "<14 6>" but the
> "of_gpiochip_init_valid_mask" drops the range and this is not expected behavior.

On top of that, it would be nice to be sure that at least all current
in-kernel users (meaning all DTS provided so far by the kernel) do
interpret it as start,size. Otherwise this will be an (unacceptable)
ABI change and hence documentation would need to be fixed with
variable names in the code.

-- 
With Best Regards,
Andy Shevchenko