linux-kernel - Re: [PATCH v5 08/12] gpio: aggregator: export symbols of the GPIO forwarder library

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Message-ID: <CAMuHMdUtEtZH0MuS7TA6RTa1-LB=K47sEGzo9BJM_RvfCRmRAw@mail.gmail.com>
Date: Mon, 12 May 2025 16:39:40 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Thomas Richard <thomas.richard@...tlin.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Bartosz Golaszewski <brgl@...ev.pl>, 
	Kees Cook <kees@...nel.org>, Andy Shevchenko <andy@...nel.org>, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com, 
	DanieleCleri@...on.eu, GaryWang@...on.com.tw, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v5 08/12] gpio: aggregator: export symbols of the GPIO
 forwarder library

Hi Thomas,

On Mon, 12 May 2025 at 16:08, Thomas Richard <thomas.richard@...tlin.com> wrote:
> On 5/9/25 11:07, Geert Uytterhoeven wrote:
> > On Tue, 6 May 2025 at 17:21, Thomas Richard <thomas.richard@...tlin.com> wrote:
> >> Export all symbols and create header file for the GPIO forwarder library.
> >> It will be used in the next changes.
> >>
> >> Signed-off-by: Thomas Richard <thomas.richard@...tlin.com>
>
> ...
>
> >> +
> >> +int gpio_fwd_set_config(struct gpio_chip *chip, unsigned int offset,
> >> +                       unsigned long config);
> >> +
> >> +int gpio_fwd_to_irq(struct gpio_chip *chip, unsigned int offset);
> >
> > I would expect all of these to take gpiochip_fwd pointers instead of
> > gpio_chip pointers.  What prevents you from passing a gpio_chip pointer
> > that does not correspond to a gpiochip_fwd object, causing a crash?
>
> Indeed nothing prevents from passing gpio_chip pointer which does not
> correspond to a gpiochip_fwd object.
> And it is also a bit weird to pass a gpiochip_fwd pointer in some cases
> (for example gpio_fwd_gpio_add()) and a gpio_chip in other cases.
>
> I can keep GPIO operations as is, and create exported wrappers which
> take a gpiochip_fwd pointer as parameter, for example:
>
> int gpiochip_fwd_get_multiple(struct gpiochip_fwd *fwd,
>                               unsigned long *mask,
>                               unsigned long *bits)
> {
>         struct gpio_chip *gc = gpiochip_fwd_get_gpiochip(fwd);
>
>         return gpio_fwd_get_multiple_locked(chip, mask, bits);
> }
> EXPORT_SYMBOL_NS_GPL(gpiochip_fwd_get_multiple, "GPIO_FORWARDER");
>
> So exported functions are gpiochip_fwd_*().

That sounds fine to me.

BTW, do you need to use these functions as gpio_chip callbacks?
If that is the case, they do no need to take struct gpio_chip pointers.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds