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

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Message-ID: <CAMuHMdUMVFk+-3akj6nj+XCya9zj_FqkbnpOT1Wc4wSsgttiww@mail.gmail.com>
Date: Mon, 12 May 2025 17:14:42 +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 17:01, Thomas Richard <thomas.richard@...tlin.com> wrote:
> On 5/12/25 16:39, Geert Uytterhoeven wrote:
> > 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.
> >
> I'm not sure to understand the question, or the idea behind the question.

Do users of the forwarder library want to use these functions directly
as callbacks in their own gpiochip?
E.g. do they want to use:

    chip->get_multiple_rv = gpiochip_fwd_get_multiple;

I hope my question is more clear now.
Thanks!

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