Re: [PATCH] pinctrl: msm: allow the gpio base to be configurable

[Bartosz Golaszewski <brgl@xxxxxxxx>]

2018-01-26 14:16 GMT+01:00 Timur Tabi <timur@xxxxxxxxxxxxxx>:
> On 1/26/18 7:01 AM, Linus Walleij wrote:
>>
>> This is a feature not a bug. It encourages people not to
>> depend on the global GPIO numberspace.
>>
>> Just set it to -1.
>
>
> If I change it to -1, then I think I'm going to break every existing MSM
> platform that depends on the base address being 0, because then every MSM
> driver will have a non-zero base, and none of the existing drivers register
> more than one GPIO device.
>
> So how about this:
>
>         static int base = 0;
>
>         chip->base = base;
>         base = -1;
>
> This way, existing code works as before.  If any driver registers two GPIO
> devices, the first one will get a base of 0, and the second one will get
> some other base.
>
>>> gpiochip_find_base: found new base at 437
>>
>> (...)
>>>
>>> gpiochip_find_base: found new base at 362
>>
>> These are awesome bases, just beautiful. Use this.
>>
>> If you don't like seeing GPIO base numbers like this: use things
>> like the chardev and the tools in tools/gpio or libgpiod when
>> developing, and you will never see them. They should not make
>> a difference anyway.
>
>
> Can you tell me more about the chardev?  I've always been using "echo X >
> /sys/class/gpio/export", so I guess that's not the right way to do things.
>

Hi Timur,

take a look at the in-project documentation[1] and read the article[2]
about libgpiod. That should get you started.

Let me know if anything's not clear.

Thanks,
Bartosz

[1] https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/
[2] https://www.cnx-software.com/2017/11/03/learn-more-about-linuxs-new-gpio-user-space-subsystem-libgpiod/
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