linux-kernel - Re: Define LEDs with mixed colors

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Date:   Mon, 1 Nov 2021 13:18:40 +0100
From:   Pavel Machek <pavel@....cz>
To:     "hamza.farooq@...mens.com" <hamza.farooq@...mens.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        "henning.schild@...mens.com" <henning.schild@...mens.com>,
        "jan.kiszka@...mens.com" <jan.kiszka@...mens.com>,
        "Haeussler, Gerd" <gerd.haeussler.ext@...mens.com>
Subject: Re: Define LEDs with mixed colors

Hi!

> > > I am toying with the idea of writing a multicolor LED GPIO driver. What
> > would be the right way to define mixed color LEDs (for leds-gpio), in device
> > tree or ACPI?
> > > Consider the following:
> > >
> > > leds {
> > > 	compatible = "gpio-leds";
> > > 	led0 {
> > > 		gpios = <&mcu_pio 0 GPIO_ACTIVE_LOW>;
> > > 		color = <LED_COLOR_ID_RED>;
> > > 	};
> > >
> > > 	led1 {
> > > 		gpios = <&mcu_pio 1 GPIO_ACTIVE_HIGH>;
> > > 		color = <LED_COLOR_ID_GREEN>;
> > > 	};
> > > 	led2 {
> > > 		gpios = <&mcu_pio 0 GPIO_ACTIVE_LOW
> > > 			&mcu_pio 1 GPIO_ACTIVE_LOW>;
> > > 		color = <LED_COLOR_ID_AMBER>;
> > > 	};
> > > };
> > >
> > > This probably won't work as "gpios" seem to be single object in gpio-leds
> > driver code, but what can I do to achieve something similar?
> > > It is important to define this LED in DT/ACPI in order for the user app to see
> > it in the /sys/class/led folder, without having to write platform-specific
> > driver.
> > >
> > 
> > So you have one package with red and green LED, each connected to one
> > GPIO?
> Right. It is possible to create orange color, and I want to use DT/ACPI to present this info to the userland.
> 
> > 
> > Can you take a look at Documentation/leds/leds-class-multicolor.rst?
> Couldn't find a hint there therefore this email thread. I might eventually write a multicolor led-gpio driver so want to know how to handle mixed LED.
>

There's no similar driver in the tree, and we don't have estabilished
API. You are mostly on your own.

Best regards,
								Pavel

-- 
http://www.livejournal.com/~pavelmachek

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