Re: [PATCH] gpio: Allow user to customise maximum number of GPIOs

Christophe Leroy
2022-08-28T09:06:41Z

Le 26/08/2022 à 23:54, Linus Walleij a écrit :
> On Fri, Aug 26, 2022 at 5:08 PM Christophe Leroy
> <christophe.leroy@csgroup.eu> wrote:
>> Le 26/08/2022 à 15:49, Linus Walleij a écrit :
>>> On Thu, Aug 25, 2022 at 4:00 PM Christophe Leroy
>>> <christophe.leroy@csgroup.eu> wrote:
>>>
>>>>> Christophe? Will you take a stab at it?
>>>>
>>>> Which patch should I write ?
>>>
>>> One that removes CONFIG_ARCH_HAS_NR_GPIO entirely, then
>>> allocate bases for new GPIO chips from 0 and upward instead.
>>> And then see what happens.
>>>
>>
>> Ok, I can give it a try.
>
> Nice!
>
>> But what do I do with:
>>
>> drivers/gpio/gpio-aggregator.c: bitmap = bitmap_alloc(ARCH_NR_GPIOS,
>> GFP_KERNEL);
>
> That's just used locally in that driver to loop over the arguments to the
> aggregator (from the file in sysfs). I would set some arbitrary root
> like
> #define AGGREGATOR_MAX_GPIOS 512
> and just search/replace with that.
>

And what about gsta_gpio_setup() that requests base 0 with the following
comment:

/*
* ARCH_NR_GPIOS is currently 256 and dynamic allocation starts
* from the end. However, for compatibility, we need the first
* ConneXt device to start from gpio 0: it's the main chipset
* on most boards so documents and drivers assume gpio0..gpio127
*/

And I guess there might be other drivers like that (I found that one
because of its comment mentionning ARCH_NR_GPIOS.

Another solution could be to leave first GPIOs for static allocation,
and allocate dynamic ones from 256 or from 512 ?

Maybe in two steps:
- First step: Allocate dynamic from 256 upwards and add a pr_warn() for
all static allocations.
- Second step later: Allocate dynamic from 0 and forbid static allocation.

Any opinion ?

Christophe