From: Linus Walleij <linus.walleij@linaro.org>
To: Arnd Bergmann <arnd@arndb.de>,
Alexandre Courbot <gnurou@gmail.com>,
Alexandre Courbot <acourbot@nvidia.com>,
Bartosz Golaszewski <brgl@bgdev.pl>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>,
Jonathan Corbet <corbet@lwn.net>,
Russell King <linux@armlinux.org.uk>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>,
"moderated list:ARM PORT" <linux-arm-kernel@lists.infradead.org>,
"open list:GENERIC INCLUDE/ASM HEADER FILES"
<linux-arch@vger.kernel.org>
Subject: Re: [PATCH] gpio: Allow user to customise maximum number of GPIOs
Date: Thu, 18 Aug 2022 14:25:39 +0200 [thread overview]
Message-ID: <CACRpkda0+iy8H0YmyowSDn8RbYgnVbC1k+o5F67inXg4Qb934Q@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a0j-54_OkXC7x3NSNaHhwJ+9umNgbpsrPxUB4dwewK63A@mail.gmail.com>
On Thu, Aug 18, 2022 at 1:33 PM Arnd Bergmann <arnd@arndb.de> wrote:
> On Thu, Aug 18, 2022 at 1:13 PM Linus Walleij <linus.walleij@linaro.org> wrote:
> > static inline bool gpio_is_valid(int number)
> > {
> > return number >= 0 && number < ARCH_NR_GPIOS;
> > }
> >
> > ?
> >
> > If using GPIO descriptors, any descriptor != NULL is valid,
> > this one is just used with legacy GPIOs. Maybe we should just
> > delete gpio_is_valid() everywhere and then drop the cap?
>
> I think it makes sense to keep gpio_is_valid() for as long as we
> support the numbers.
Hmmm....
> > I think there may be systems and users that still depend on GPIO base
> > numbers being assigned from ARCH_NR_GPIOS and
> > downwards (userspace GPIO numbers in sysfs will also change...)
> > otherwise we could assign from 0 and up.
>
> Is it possible to find in-kernel users that depend on well-known
> numbers for dynamically assigned gpios? I would argue
> that those are always broken.
Most in-kernel users hard-code the base to something like
0 etc it's only the ones that code -1 into .base that are in
trouble because that will activate dynamic assignment for the
base.
git grep 'base = -1' yields these suspects:
arch/arm/common/sa1111.c: sachip->gc.base = -1;
arch/arm/common/scoop.c: devptr->gpio.base = -1;
arch/powerpc/platforms/52xx/mpc52xx_gpt.c: gpt->gc.base = -1;
arch/powerpc/platforms/83xx/mcu_mpc8349emitx.c: gc->base = -1;
That's all! We could just calculate these to 512-ngpios and
hardcode that instead.
> Even for the sysfs interface, it is questionable to rely on
> specific numbers because at least in an arm multiplatform
> kernel the top number changes based on kernel configuration.
Yeah :/ still these users tend to angrily report any breakage
due to expected (fragile) behaviour.
> > Right now the safest would be:
> > Assign from 512 and downwards until we hit 0 then assign
> > from something high, like U32_MAX and downward.
> >
> > That requires dropping gpio_is_valid() everywhere.
> >
> > If we wanna be bold, just delete gpio_is_valid() and assign
> > bases from 0 and see what happens. But I think that will
> > lead to regressions.
>
> I'm still unsure how removing gpio_is_valid() would help.
If we allow GPIO base all the way to U32_MAX
this function becomes:
static inline bool gpio_is_valid(int number)
{
return number >= 0 && number < U32_MAX;
}
and we can then just
#define gpio_is_valid true
and in that case it is better to delete the use of this function
altogether since it can not fail.
> What I could imagine as a next step would be to mark all
> consumer drivers and the sysfs interface that use gpio
> numbers as 'depends on GPIO_LEGACY' and then only
> provide the corresponding drivers if that option is set.
Hm I wonder what Bartosz and Alexandre Courbot and thinks
about a GPIO_LEGACY symbol to phase out the global
GPIO numberspace. I kind of like the idea.
I made the sysfs depend on CONFIG_EXPERT to at least make it less
accessible and not provide users with guns to shoot themselves
in the foot.
Yours,
Linus Walleij
next prev parent reply other threads:[~2022-08-18 12:25 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-09 10:40 [PATCH] gpio: Allow user to customise maximum number of GPIOs Christophe Leroy
2022-08-11 19:57 ` H. Peter Anvin
2022-08-12 21:58 ` Andy Shevchenko
2022-08-12 23:21 ` H. Peter Anvin
2022-08-17 17:21 ` Christophe Leroy
2022-08-17 17:46 ` Arnd Bergmann
2022-08-18 6:00 ` Christophe Leroy
2022-08-18 8:25 ` Arnd Bergmann
2022-08-18 9:33 ` Linus Walleij
2022-08-18 9:47 ` Arnd Bergmann
2022-08-18 11:13 ` Linus Walleij
2022-08-18 11:33 ` Arnd Bergmann
2022-08-18 12:25 ` Linus Walleij [this message]
2022-08-18 12:46 ` Arnd Bergmann
2022-08-18 13:11 ` Christophe Leroy
2022-08-25 13:36 ` Linus Walleij
2022-08-25 14:00 ` Christophe Leroy
2022-08-26 13:49 ` Linus Walleij
2022-08-26 15:08 ` Christophe Leroy
2022-08-26 21:54 ` Linus Walleij
2022-08-28 9:06 ` Christophe Leroy
2022-08-28 10:04 ` Arnd Bergmann
2022-08-30 7:58 ` Davide Ciminaghi
2022-08-31 13:32 ` Linus Walleij
2022-08-31 14:12 ` Davide Ciminaghi
2022-08-31 21:07 ` Andy Shevchenko
2022-08-31 21:48 ` Davide Ciminaghi
2022-08-30 8:33 ` Alessandro Rubini
2022-08-30 9:03 ` Christophe Leroy
2022-08-28 11:35 ` Linus Walleij
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