Re: [PATCH] gpio: omap: make gpio numbering deterministical by using of aliases

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Wed, Jun 15, 2016 at 9:24 AM, Uwe Kleine-König
<u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
> On Wed, Jun 15, 2016 at 08:56:58AM +0200, Linus Walleij wrote:

>> The GPIO numbering scheme is a matter of Linux internals and
>> not about hardware description IMO.
>
> Not sure if I should agree here or not. It's very usual that the
> "internal" gpio numbers match the hardware reference manual. I know this
> from imx, at91, all pre-dt platforms, I'm sure there are more, and I bet
> I'm not the only one relying on this for omap.

I think it will still match nicely against the chip-local offsets of the
primary gpiochip so it'll be fine with a chardev too. The same was/is
the case of the first interrupts on x86 I think, but with the plethora of
irqchips and dependency on probe order etc the assumption is
nowadays to dangerous.

>
> And this is very usual in the dt world, too:
>
> $ git grep -El 'gpio. = \&gpio' arch/arm/boot/dts | wc -l
> 37

Aha I didn't even know. Well I guess I could allow it for OMAP too
then, but I want an ACK from one of the DT binding maintainers.

>> The way forward is to use the character device and use gpiochip
>> devices with offset indexes and look up GPIOs by name from the
>> character devices. If nothing substantial happens I am merging the
>> final pieces of the GPIO chardev ABI for v4.8 and that is doing all that
>> sysfs was doing and then some. I just need to change a small thing
>> before sending the final version for review.
>
> Hmm, so /sys/class/gpio was obsoleted before the substitution was ready?

Yeah, the sysfs was so broken that it could not be maintained.

> I'd say an overlapping of several kernel versions would be good as we
> cannot expect that userspace changes as fast as the kernel.

This is why it is scheduled for removal in 2020 and not tomorrow.

> Independent of the inclusion of my patch series in the mainline kernel
> I'll have to use it on my custom kernel to keep the hardware do what it
> should.

Nah well, let's discuss it.

Yours,
Linus Walleij
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