Re: [PATCH] gpiolib: Disallow identical line names in the same chip

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

Hi Linus,

On Sat, Dec 12, 2020 at 1:36 AM Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
> We need to make this namespace hierarchical: at least do not
> allow two lines on the same chip to have the same name, this
> is just too much flexibility. If we name a line on a chip,
> name it uniquely on that chip.
>
> I don't know what happens if we just apply this, I *hope* there
> are not a lot of systems out there breaking this simple and
> intuitive rule.
>
> As a side effect, this makes the device tree naming code
> scream a bit if names are not globally unique.
>
> I think there are not super-many device trees out there naming
> their lines so let's fix this before the problem becomes
> widespread.
>
> Cc: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> Cc: Johan Hovold <johan@xxxxxxxxxx>
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---
> This may be just the first step in tightening this up.
> Googling gives at hand that the colission warning doesn't
> happen much so we might go as far as to say the name can
> be required to be globally unique, but that creates a flat
> namespace so I don't know if that is desireable.

As the names are specified in DT, I think the biggest "use case" for
collisions is GPIO chips on expansion boards, if multiple instances
of the same board can be connected.

This is a bit similar to clock outputs, cfr. commit f491276a51685987
("clk: vc5: Allow Versaclock driver to support multiple instances"), but
in the clock case, the name of the clock output is dictated by the
driver, not by DT.

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