Le 18/08/2022 à 14:46, Arnd Bergmann a écrit :

On Thu, Aug 18, 2022 at 2:25 PM Linus Walleij [off-list ref] wrote:

quoted

On Thu, Aug 18, 2022 at 1:33 PM Arnd Bergmann [off-list ref] wrote:

quoted

On Thu, Aug 18, 2022 at 1:13 PM Linus Walleij [off-list ref] wrote:

quoted

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?

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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.

What about GPIO AGGREGATOR, drivers/gpio/gpio-aggregator.c

	bitmap = bitmap_alloc(ARCH_NR_GPIOS, GFP_KERNEL);


Christophe
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