6. LED

6.1. Introduction

There are 2 LEDs on the AIO-3576Q development board, as the following table shows:

LED	Pin name	Pin number
Yellow	GPIO3_A2	98
Green	GPIO3_A3	99

LEDs can be controlled by using the LED device subsystem or by directly operating GPIO.

6.2. Controlling LEDs by device

Linux has its own LED subsystem for LED devices. In iCore-3576Q, LEDs are configured as LED class devices.You can control them via /sys/class/leds/.

The default status of the three on-board leds are:

• Yellow: Turn on after the system powers on

• Green: defined by user

You can change the behavior of each LED by using the echo command to write command to its brightness property:

echo 0 >/sys/class/leds/:user/brightness  // led off
echo 255 >/sys/class/leds/:user/brightness  // led on

6.3. Using trigger control LED

Trigger contains a variety of ways to control the LED, here with two examples to illustrate.

• Simple trigger LED

• Complex trigger LED

For more information, please read the document leds-class.txt.

First of all, we need to know how many LED definition, while the corresponding property of the LED is.

Defined LED node in file kernel/arch/arm64/boot/dts/rockchip/rk3576-firefly-aio-3576q.dtsi, like this:

#if LED_GPIO_OR_PWM
	firefly_leds: leds {
		compatible = "pwm-leds";
		status = "okay";
		power_led {
			label = ":power";
			pwms = <&pwm2_8ch_0 0 50000 0>; //blue
			max-brightness = <255>;
			default-state = "on";
			linux,default-trigger = "ir_led";
		};
		user_led {
			label = ":user";
			pwms = <&pwm2_8ch_2 0 50000 0>; //red
			max-brightness = <255>;
			default-state = "off";
			linux,default-trigger = "none";
		};
		diy_led {
			label = ":diy";
			pwms = <&pwm2_8ch_1 0 50000 0>; //green
			max-brightness = <255>;
			default-state = "off";
			linux,default-trigger = "none";
		};
	};
#else
	firefly_leds: leds {
		compatible = "gpio-leds";
		status = "okay";
		power_led: power {
			label = ":power"; //blue led
			linux,default-trigger = "ir-power-click";
			default-state = "on";
			gpios = <&gpio2 RK_PD0 GPIO_ACTIVE_HIGH>;
			pinctrl-names = "default";
			pinctrl-0 = <&led_power>;
		};
		user_led: user {
			label = ":user"; //red led
			linux,default-trigger = "ir-user-click";
			default-state = "off";
			gpios = <&gpio2 RK_PD2 GPIO_ACTIVE_HIGH>;
			pinctrl-names = "default";
			pinctrl-0 = <&led_user>;
		};
		diy_led: diy {
			label = ":diy"; //green led
			linux,default-trigger = "ir-user-click";
			default-state = "off";
			gpios = <&gpio2 RK_PD1 GPIO_ACTIVE_HIGH>;
			pinctrl-names = "default";
			pinctrl-0 = <&led_diy>;
		};
	};
#endif

Note: The value of compatible must match the one in drivers/leds/leds-gpio.c.

6.3.1. Simple trigger LED

It is a simple trigger mode to control LEDs, please refer to kernel/drivers/leds/trigger/led-firefly-demo.c

6.3.2. Complex trigger LED

The following is the trigger mode control LED complex example, timer trigger is to let the LED to achieve constant on/off effect.

We need to configure the timer trigger on the kernel.

In the kernel-5.10 path using make menuconfig, in accordance with the following method to chose timer trigger driver.

Device Drivers
--->LED Support
   --->LED Trigger support
      --->LED Timer Trigger

LED Timer Trigger should be enabled by default. If not, enable it, save defconfig and re-build kernel to take effect.

Echo “timer” to trigger then we can see LED starts to blink.

echo "timer" > /sys/class/leds/:user/trigger

The user can also use the cat command to get the available values for the trigger:

# cat /sys/class/leds/:user/trigger
none ir-power-click rfkill-any rfkill-none test_ac-online test_battery-charging-or-full 
test_battery-charging test_battery-full test_battery-charging-blink-full-solid 
test_usb-online mmc0 [timer] heartbeat backlight default-on ir-user-click mmc1 
rfkill0 tcpm-source-psy-6-0022-online rfkill1 rfkill2