LED

Introduction

There are 3 LEDs on the ROC-RK3576-PC development board, as the
following table shows:

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 ROC-RK3576-PC,
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:

Blue:   Turn on after the system powers on.

Red:    defined by user.

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

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/ROC-
RK3576-PC.dts.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