From: Arnd Bergmann <arnd@arndb.de>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
Alexandre Courbot <gnurou@gmail.com>,
Alexandre Courbot <acourbot@nvidia.com>,
Bartosz Golaszewski <brgl@bgdev.pl>,
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 14:46:23 +0200 [thread overview]
Message-ID: <CAK8P3a0uuJ_z8wmNmQTW_qPNqzz7XoxZdHgqbzmK+ydtjraeHg@mail.gmail.com> (raw)
In-Reply-To: <CACRpkda0+iy8H0YmyowSDn8RbYgnVbC1k+o5F67inXg4Qb934Q@mail.gmail.com>
On Thu, Aug 18, 2022 at 2:25 PM Linus Walleij <linus.walleij@linaro.org> wrote:
> 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:
> > > 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.
How do the consumers find the numbers for these four?
> > > 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.
S32_MAX might be a better upper bound. That allows to
just have no number assigned to a gpio chip. Any driver
code calling desc_to_gpio() could then get back -1
or a negative error code.
Making the ones that are invalid today valid sounds like
a step backwards to me if the goal is to stop using
gpio numbers and most consumers no longer need them.
Arnd
next prev parent reply other threads:[~2022-08-18 12:46 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
2022-08-18 12:46 ` Arnd Bergmann [this message]
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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