linux-kernel - Re: [PATCH 0/4] gpio: mxc: silence warning about GPIO base being statically allocated

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Message-ID: <CAMRc=MewWr8nrUBgWe+ckTuVdmLC=grkw1aWeXnWszcaBZvZvQ@mail.gmail.com>
Date: Thu, 23 Jan 2025 10:19:26 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Ahmad Fatoum <a.fatoum@...gutronix.de>
Cc: Andy Shevchenko <andy.shevchenko@...il.com>, Linus Walleij <linus.walleij@...aro.org>, 
	Andy Whitcroft <apw@...onical.com>, Joe Perches <joe@...ches.com>, 
	Dwaipayan Ray <dwaipayanray1@...il.com>, Lukas Bulwahn <lukas.bulwahn@...il.com>, 
	Fabio Estevam <festevam@...il.com>, Shawn Guo <shawnguo@...nel.org>, 
	Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>, 
	Dario Binacchi <dario.binacchi@...rulasolutions.com>, Haibo Chen <haibo.chen@....com>, 
	Catalin Popescu <catalin.popescu@...ca-geosystems.com>, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, imx@...ts.linux.dev, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/4] gpio: mxc: silence warning about GPIO base being
 statically allocated

On Tue, Jan 21, 2025 at 11:37 AM Ahmad Fatoum <a.fatoum@...gutronix.de> wrote:
>
> Hello Bartosz,
>
> On 15.01.25 17:52, Bartosz Golaszewski wrote:
> >
> > I recently wrote a user-space compatibility layer for sysfs[1]. While
> > right now it doesn't support static base numbers, I'm very open to
> > adding it except that I wasn't sure how to approach it.
> >
> > Is this of any use to you and could it help you switch to libgpiod
> > without changing your user-space set-up (given the support for static
> > GPIO numbering)?
>
> If the goal is to have a drop-in replacement for sysfs outside
> of the kernel, I think it needs to maintain the same numbering.
>
> I am not sure I see myself using it, because the new projects are using
> libgpiod from the get-go. My issue is not with removal of sysfs, but with
> user hostile deprecation approaches.
>
> > If so, how would you like to see this implemented? A
> > config file at /etc that would list chip labels and their desired GPIO
> > base?
>
> Many GPIOs tend to not have labels. I think the mapping config file
> should rather map GPIO controllers to a base address. The same thing the
> kernel is currently doing. This assumes the numbering of the built-in
> GPIO controllers is deterministic, e.g. by consulting /aliases. I haven't
> checked, but I hope this is already the case.

Well, they will have labels, it's just that the label will be
something like "6e80000.gpio" which can very well be mapped onto a
predefined GPIO range.

The file could look like:

/etc/gpio-static-base.conf

```
6e80000.gpio 12
foobar 340
```

Where the first column is the label and the second the static base
that must be less than 512 - ngpio.

Bart