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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 17 Mar 2020 09:48:08 +0100
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Subject: Re: [PATCH v5 2/5] gpiolib: Add support for GPIO line table lookup
To:     Linus Walleij <linus.walleij@linaro.org>
Cc:     Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Harish Jenny K N <harish_kandiga@mentor.com>,
        Eugeniu Rosca <erosca@de.adit-jv.com>,
        Alexander Graf <graf@amazon.com>,
        Peter Maydell <peter.maydell@linaro.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Phil Reid <preid@electromag.com.au>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Christoffer Dall <christoffer.dall@arm.com>,
        Magnus Damm <magnus.damm@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
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Hi Linus,

On Thu, Mar 12, 2020 at 3:21 PM Linus Walleij <linus.walleij@linaro.org> wrote:
> On Tue, Feb 18, 2020 at 4:18 PM Geert Uytterhoeven
> <geert+renesas@glider.be> wrote:
> > Currently GPIOs can only be referred to by GPIO controller and offset in
> > GPIO lookup tables.
> >
> > Add support for looking them up by line name.
> > 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@glider.be>
> > Reviewed-by: Ulrich Hecht <uli+renesas@fpond.eu>
> > Reviewed-by: Eugeniu Rosca <erosca@de.adit-jv.com>
> > Tested-by: Eugeniu Rosca <erosca@de.adit-jv.com>
>
> I will try to understand why this change is necessary to implement
> the gpio aggregator (probablt I will comment that on the other
> patches like "aha now I see it" or so, but it would help a lot if the
> commit message
> would state the technical reason to why we need to do this change,
> like what it is that you want to do and why you cannot do it without
> this change.

It's very simple: how do you want the user to refer to a specific GPIO
line? Currently he can only do so by gpiochip label and index.
However, there exists another stable reference: the (optional) line name,
which can be attached using "gpio-line-names" in DT or ACPI.
As this is the most use-centric way to refer to a GPIO, it makes sense
to support lookup based on that, too.

Will reword to make this clearer.


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