linux-kernel - Re: [PATCH] gpiolib: Fix return value of gpio_to

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Message-ID: <CACRpkda9UAGxMrP27qYe-ZC=3RehesAPsUAnt71Jx5Dd+rpSqQ@mail.gmail.com>
Date:   Thu, 6 Dec 2018 12:54:52 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Krzysztof Kozlowski <krzk@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Janusz Krzysztofik <jmkrzyszt@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: Fix return value of gpio_to_desc() stub if !GPIOLIB

On Thu, Dec 6, 2018 at 10:45 AM Krzysztof Kozlowski <krzk@...nel.org> wrote:

> If CONFIG_GPOILIB is not set, the stub of gpio_to_desc() should return
> the same type of error as regular version: NULL.  All the callers
> compare the return value of gpio_to_desc() against NULL, so returned
> ERR_PTR would be treated as non-error case leading to dereferencing of
> error value.
>
> Fixes: 79a9becda894 ("gpiolib: export descriptor-based GPIO interface")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
> ---
>  include/linux/gpio/consumer.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
> index ed070512b40e..3b01fbcafc94 100644
> --- a/include/linux/gpio/consumer.h
> +++ b/include/linux/gpio/consumer.h
> @@ -505,7 +505,7 @@ static inline int gpiod_set_consumer_name(struct gpio_desc *desc,
>
>  static inline struct gpio_desc *gpio_to_desc(unsigned gpio)
>  {
> -       return ERR_PTR(-EINVAL);
> +       return NULL;

I suppose this is consistent with comitt:
22c403676dbbb7c6f186099527af7f065498ef45
"gpio: return NULL from gpiod_get_optional when GPIOLIB is disabled"

So in that way it should be fine.

I'm just wondering where you see this problem, because IMO
a driver that is using GPIO should either
depends on GPIOLIB or
select GPIOLIB
it is extremely uncommon for a GPIO line to actually be optional at
compile time (as opposed to optional at runtime) so I would very
much like to look closer at this.

Yours,
Linus Walleij