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From: Linus Walleij <linus.walleij@linaro.org>
To: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Peter Maydell <peter.maydell@linaro.org>,
	QEMU Developers <qemu-devel@nongnu.org>,
	Phil Reid <preid@electromag.com.au>,
	Jonathan Corbet <corbet@lwn.net>,
	Marc Zyngier <marc.zyngier@arm.com>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>,
	Magnus Damm <magnus.damm@gmail.com>,
	Christoffer Dall <christoffer.dall@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	Rob Herring <robh+dt@kernel.org>,
	Harish Jenny K N <harish_kandiga@mentor.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Alexander Graf <graf@amazon.com>,
	Eugeniu Rosca <erosca@de.adit-jv.com>
Subject: Re: [PATCH v6 4/8] gpiolib: Add support for GPIO lookup by line name
Date: Thu, 26 Mar 2020 22:18:39 +0100
Message-ID: <CACRpkdbN82n3B+Q-QVjB1jLpJAYS19fKukkDXQm3gZsuFFFM_w@mail.gmail.com> (raw)
In-Reply-To: <20200324135653.6676-4-geert+renesas@glider.be>

On Tue, Mar 24, 2020 at 2:57 PM Geert Uytterhoeven
<geert+renesas@glider.be> 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@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 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.

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.

Yours,
Linus Walleij


  reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-24 13:53 [PATCH v6 0/8] gpio: Add GPIO Aggregator Geert Uytterhoeven
2020-03-24 13:56 ` [PATCH v6 1/8] ARM: integrator: impd1: Use GPIO_LOOKUP() helper macro Geert Uytterhoeven
2020-03-24 13:56   ` [PATCH v6 2/8] i2c: i801: " Geert Uytterhoeven
2020-03-25  9:14     ` Jean Delvare
2020-04-15 10:57     ` Wolfram Sang
2020-03-24 13:56   ` [PATCH v6 3/8] mfd: sm501: Use GPIO_LOOKUP_IDX() " Geert Uytterhoeven
2020-04-15  9:25     ` Lee Jones
2020-03-24 13:56   ` [PATCH v6 4/8] gpiolib: Add support for GPIO lookup by line name Geert Uytterhoeven
2020-03-26 21:18     ` Linus Walleij [this message]
2020-05-11 10:18       ` Geert Uytterhoeven
2020-03-24 13:56   ` [PATCH v6 5/8] gpiolib: Introduce gpiod_set_config() Geert Uytterhoeven
2020-03-26 21:26     ` Linus Walleij
2020-03-27  8:45       ` Geert Uytterhoeven
2020-03-27 21:33         ` Linus Walleij
2020-03-27 21:37     ` Linus Walleij
2020-03-24 13:56   ` [PATCH v6 6/8] gpio: Add GPIO Aggregator Geert Uytterhoeven
2020-03-24 13:56   ` [PATCH v6 7/8] docs: gpio: Add GPIO Aggregator documentation Geert Uytterhoeven
2020-03-24 13:56   ` [PATCH v6 8/8] MAINTAINERS: Add GPIO Aggregator section Geert Uytterhoeven
2020-03-26 21:07   ` [PATCH v6 1/8] ARM: integrator: impd1: Use GPIO_LOOKUP() helper macro Linus Walleij

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