[TOC]
LEDs provide status about the following:
- Dedicated battery state/charging state
- Chromebook power
- Adapter power
- Left side USB-C port (battery state/charging state)
- Right side USB-C port (battery state/charging state)
- Recovery mode
- Debug mode
LEDs can be configured as simple GPIOs, with on/off control only, or as PWM with adjustment brightness and color.
The CONFIG_PLATFORM_EC_LED_DT option, found in the Kconfig.led_dt file, enables devicetree based configuration of LED
policies and colors.
Enabling the devicetree LED implementation requires that you disable the legacy EC implementation.
Example:
# LED
CONFIG_PLATFORM_EC_LED_COMMON=n
Enable other config options supported in the legacy code.
LEDs are configured in two steps.
The LED colors are configured using either GPIO based LEDs or PWM based LEDs.
Configure GPIO based LEDs using cros-ec,gpio-led-pins compatible node
described by cros-ec,gpio_led_pins.yaml.
Example:
For this example, the board contains dual-channel LED, one channel turns on the blue color, and one channel turns on the amber color. To set the LED color to amber, the yellow channel is enabled and the blue channel is disabled.
gpio-led-pins {
compatible = "cros-ec,gpio-led-pins";
/* Amber - turn on yellow LED */
color_amber: color-amber {
led-pins = <&gpio_ec_chg_led_y_c1 &gpio_ec_chg_led_b_c1>;
led-values = <1 0>;
};
/* Blue - turn on blue LED */
color_blue: color-blue {
led-pins = <&gpio_ec_chg_led_y_c1 &gpio_ec_chg_led_b_c1>;
led-values = <0 1>;
};
/* White - turn on both LEDs */
color_white: color-white {
led-pins = <&gpio_ec_chg_led_y_c1 &gpio_ec_chg_led_b_c1>;
led-values = <1 1>;
};
/* Off - turn off both LEDs */
color_off: color-off {
led-pins = <&gpio_ec_chg_led_y_c1 &gpio_ec_chg_led_b_c1>;
led-values = <0 0>;
};
};
GPIO LED Pins dts file example: led_pins_herobrine.dts
Configure PWM based LEDs with two separate nodes.
The pwm-leds node, described in pwm-leds.yaml, configures the PWM channel
and frequency. The cros-ec,pwm-led-pins node, described in
cros-ec,pwm_led_pins.yaml, configures the LED colors. PWM LEDs can vary
duty-cycle percentage, providing finer color control over GPIO LEDs.
Example:
For this example, the board contains dual-channel LED, one channel controls white color intensity, and one channel controls the amber color intensity. To set the LED color to amber, the yellow channel duty-cycle is set to 100 percentage and white channel duty-cycle is set to 0.
pwmleds {
compatible = "pwm-leds";
pwm_y: pwm_y {
pwms = <&pwm2 0 PWM_HZ(100) PWM_POLARITY_INVERTED>;
};
pwm_w: pwm_w {
pwms = <&pwm3 0 PWM_HZ(100) PWM_POLARITY_INVERTED>;
};
};
pwm-led-pins {
compatible = "cros-ec,pwm-led-pins";
pwm-frequency = <100>;
/* Amber - turn on yellow LED */
color_amber: color-amber {
led-pwms = <&pwm_y &pwm_w>;
pwm-values = <100 0>;
};
/* White - turn on white LED */
color_white: color-white {
led-pwms = <&pwm_y &pwm_w>;
pwm-values = <0 100>;
};
/* Off - turn off both LEDs */
color_off: color-off {
led-pwms = <&pwm_y &pwm_w>;
pwm-values = <0 0>;
};
};
PWM LED Pins dts file example: led_pins_skyrim.dts
cros-ec,led-policy nodes describe the LED policy and set the LED behavior by
referencing cros-ec,gpio-led-pins or cros-ec,pwm-led-pins nodes.
These are described in cros-ec,led_policy.yaml
Example:
Color policies to configure physical behavior of an LED
e.g. If you want an LED to blink, create 2 color policies, one to turn on the LED and one to turn off the LED.
color-0 {
led-color = <&color_amber>;
period-ms = <1000>;
};
color-1 {
led-color = <&color-off>;
period-ms = <1000>;
};
To tie this behavior with a system state, properties defining system state and
color policies are added to cros-ec,led-policy node.
e.g. To add a blinking behavior for a system state where charge-state is "LED_PWR_STATE_DISCHARGE" and chipset-state is "POWER_S3", a policy node is defined as below.
led-policy {
compatible = "cros-ec,led-policy";
...
...
power-state-discharge-s3 {
charge-state = "LED_PWR_STATE_DISCHARGE";
chipset-state = "POWER_S3";
/* Amber 1 sec, off 3 sec */
color-0 {
led-color = <&color_amber>;
period-ms = <1000>;
};
color-1 {
led-color = <&color_off>;
period-ms = <3000>;
};
};
...
...
}
Note: It is recommended to split the policy specification and the pins specification into two devicetree files. e.g. led_policy_skyrim.dts, led_pins_skyrim.dts
LED policy dts file examples led_policy_skyrim.dts, led_policy_herobrine.dts
None
The LEDs are controlled by hook task in the file led_driver/led.c.
TODO: Enable support for ledtest
- Look for the gpio/pwm pins in the schematic with which the LEDs are attached to.
- In the above snippet, LEDs are configured to use PWM pins and attached to PWM2 and PWM3.
- Add PWM config nodes as shown in pwm-leds.yaml and led_pins_skyrim.dts.
- Add pin nodes based on the color of the LEDs attached as shown in
cros-ec,pwm_led_pins.yaml and led_pins_skyrim.dts. Name the nodes according
to the LED color for readability. e.g.
color-amber - Based on the device LED policy, create led_policy nodes as shown in cros-ec,led_policy.yaml and led_policy_skyrim.dts.