Re: [PATCH] [RFC] gpiolib: introduce gpio_name() helper

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

Hi Arnd,

On Mon, 29 Jun 2026 at 19:54, Arnd Bergmann <arnd@arndb.de> wrote:
> On Mon, Jun 29, 2026, at 17:29, Geert Uytterhoeven wrote:
> > On Mon, 29 Jun 2026 at 15:59, Arnd Bergmann <arnd@kernel.org> wrote:
> >> From: Arnd Bergmann <arnd@arndb.de>
> >>
> >> Most remaining users of desc_to_gpio() only call it for printing debug
> >> information.
> >>
> >> Replace this with a new gpiod_name() helper that returns the
> >> gpio_desc->name string after checking the gpio_desc pointer.
> >>
> >> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

> >> --- a/drivers/gpio/gpio-aggregator.c
> >> +++ b/drivers/gpio/gpio-aggregator.c
> >> @@ -758,8 +758,8 @@ int gpiochip_fwd_desc_add(struct gpiochip_fwd *fwd, struct gpio_desc *desc,
> >>
> >>         fwd->descs[offset] = desc;
> >>
> >> -       dev_dbg(chip->parent, "%u => gpio %d irq %d\n", offset,
> >> -               desc_to_gpio(desc), gpiod_to_irq(desc));
> >> +       dev_dbg(chip->parent, "%u => gpio %s irq %d\n", offset,
> >> +               gpiod_name(desc), gpiod_to_irq(desc));
> >>
> >>         return 0;
> >>  }
> >
> > Before, this printed:
> >
> >     gpio-aggregator gpio-aggregator.1: 0 => gpio 589 irq 188
> >     gpio-aggregator gpio-aggregator.1: 1 => gpio 590 irq 189
> >
> > After, this prints:
> >
> >     gpio-aggregator gpio-aggregator.1: 0 => gpio (null) irq 188
> >     gpio-aggregator gpio-aggregator.1: 1 => gpio (null) irq 189
> >
> > Same results for instantiation using sysfs or configfs[1], although
> > the latter does have optional support for specifying the name.
>
> I wonder how many of the other instances have the same problem
> then. Would it be appropriate for gpiochip_fwd_desc_add() to set
> a name itself to address this one?

I don't think it would be appropriate for the GPIO aggregator to set
that name.  What we want to print here (for debugging) is the physical
GPIO that an aggregator's GPIO is mapped to, not some consumer or line
name (which is not guaranteed to be unique).
E.g. "<chip-name>.<offset>" would be fine.  As gpiod_name() can only
return a fixed string or an existing string, it can't return such a
formatted string, though. And consumers don't have access to chip info?

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