linux-kernel - Re: [PATCH] leds: leds-dual-gpio: Add dual GPIO LEDs driver

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Message-ID: <2315048.uTtSMl1LR1@ada>
Date:   Fri, 12 Mar 2021 09:31:58 +0100
From:   Alexander Dahl <ada@...rsis.com>
To:     linux-leds@...r.kernel.org
Cc:     Hermes Zhang <chenhui.zhang@...s.com>, Pavel Machek <pavel@....cz>,
        Dan Murphy <dmurphy@...com>, kernel@...s.com,
        Hermes Zhang <chenhuiz@...s.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] leds: leds-dual-gpio: Add dual GPIO LEDs driver

Hallo Hermes,

thanks for your effort.

Am Donnerstag, 11. März 2021, 14:04:08 CET schrieb Hermes Zhang:
> From: Hermes Zhang <chenhuiz@...s.com>
> 
> Introduce a new Dual GPIO LED driver. These two GPIOs LED will act as
> one LED as normal GPIO LED but give the possibility to change the
> intensity in four levels: OFF, LOW, MIDDLE and HIGH.

Interesting use case. Is there any real world hardware wired like that you 
could point to?

> +config LEDS_DUAL_GPIO
> +	tristate "LED Support for Dual GPIO connected LEDs"
> +	depends on LEDS_CLASS
> +	depends on GPIOLIB || COMPILE_TEST
> +	help
> +	  This option enables support for the two LEDs connected to GPIO
> +	  outputs. These two GPIO LEDs act as one LED in the sysfs and
> +	  perform different intensity by enable either one of them or both.

Well, although I never had time to implement that, I suspect that could 
conflict if someone will eventually write a driver for two pin dual color LEDs 
connected to GPIO pins.  We actually do that on our hardware and I know others 
do, too.

I asked about that back in 2019, see this thread:

https://www.spinics.net/lists/linux-leds/msg11665.html

At the time the multicolor framework was not yet merged, so today I would 
probably make something which either uses the multicolor framework or at least 
has a similar interface to userspace. However, it probably won't surprise you 
all, this is not highest priority on my ToDo list. ;-)

(What we actually do is pretend those are separate LEDs and ignore the 
conflicting case where both GPIOs are on and the LED is dark then.)

Greets
Alex