Re: Replacing global GPIO numbers in sysfs with hardware offsets

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Linus,

On Fri, 28 Feb 2025 at 08:50, Linus Walleij <linus.walleij@linaro.org> wrote:
> On Wed, Feb 26, 2025 at 1:43 PM Marek Vasut <marex@denx.de> wrote:
> > > I understand, I'm fine with sysfs if it needs to be a "support forever"
> > > ABI, as long as it's:
> > >
> > > - Using the per-chip HW numberspace
> >
> > This is no issue for me.

So that would be 0..<N-1>, not <base>..<base+N-1>?
Hence you cannot have global (un)export files in sysfs, but need
per-chip (un)export files?

> > > - Doesn't need any echo NN > export to see the lines in
> > >    sysfs.
> >
> > Can we really make do without export/unexport ?
>
> I was more thinking that we should not need export/unexport
> just to see the line. Propsal elsewhere in this thread:
>
> /sys/bus/gpio/gpiochip0
> /sys/bus/gpio/gpiochip0/gpio0
> /sys/bus/gpio/gpiochip0/gpio0/userspace
> /sys/bus/gpio/gpiochip0/gpio0/value
> /sys/bus/gpio/gpiochip0/gpio1
> /sys/bus/gpio/gpiochip0/gpio1/userspace
> /sys/bus/gpio/gpiochip0/gpio1/value
>
> Take a GPIO, shake it, give it back to the kernel:
> echo 1 > /sys/bus/gpio/gpiochip0/gpio1/userspace
> echo 0 > /sys/bus/gpio/gpiochip0/gpio1/value
> sleep 1
> echo 1 > /sys/bus/gpio/gpiochip0/gpio1/value
> echo 0 > /sys/bus/gpio/gpiochip0/gpio1/userspace
>
> So we can always "see" this GPIO line, instead of
> exporting/unexporting there is a knob to assign/unassign
> it to userspace.

Why would you want to always "see" all GPIO lines?
What is the use case for that? What am I missing?

If it is recommended not to use this interface, I think all GPIOs
should be invisible by default.  Hence I still prefer the (un)export
interface.

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds