Re: [PATCH v6 4/8] gpiolib: Add support for GPIO lookup by line name

[Geert Uytterhoeven]

Hi Linus,

On Thu, Mar 26, 2020 at 10:18 PM Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
> On Tue, Mar 24, 2020 at 2:57 PM Geert Uytterhoeven
> <geert+renesas@xxxxxxxxx> wrote:
> > Currently a GPIO lookup table can only refer to a specific GPIO by a
> > tuple, consisting of a GPIO controller label and a GPIO offset inside
> > the controller.
> >
> > However, a GPIO may also carry a line name, defined by DT or ACPI.
> > If present, the line name is the most use-centric way to refer to a
> > GPIO.  Hence add support for looking up GPIOs by line name.
> >
> > Implement this by reusing the existing gpiod_lookup infrastructure.
> > Rename gpiod_lookup.chip_label to gpiod_lookup.key, to make it clear
> > that this field can have two meanings, and update the kerneldoc and
> > GPIO_LOOKUP*() macros.
> >
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> > Reviewed-by: Ulrich Hecht <uli+renesas@xxxxxxxx>
> > Reviewed-by: Eugeniu Rosca <erosca@xxxxxxxxxxxxxx>
> > Tested-by: Eugeniu Rosca <erosca@xxxxxxxxxxxxxx>
>
> I kind of like this approach, however there are things here that
> need to be considered: the line name is in no way globally unique,
> and I think there are already quite a few GPIO chips that
> have the same line names assigned for every instance of that
> chip.
>
> gpiochip_set_desc_names() only warns if there is a line with
> the same name on the same gpio_chip.

on a _different_ gpio chip.

> I suppose we need to document that the line name look-up
> will be on a first-come-first-served basis: whatever line
> we find first with this name is what you will get a reference
> to, no matter what chip it is on, and it is possible albeit
> not recommended that some other chip has a line with the
> same name.

Agreed.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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