LED

Introduction

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

Controlling LEDs by device

Linux has its own LED subsystem for LED devices. In iCore-3576JQ, 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:

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

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-3576jq.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".

Simple trigger LED

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

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