Linux kernel configuration - INPUT_LEDS

jakthree · August 2, 2021, 5:50pm

Kernel 5.11.10
I enabled ‘Export input device LEDs in sysfs’ (INPUT_LEDS) in my kernel .config because it has ‘INPUT’ and ‘LED’ in it’s name. However I’m not sure what the purpose of INPUT_LEDS. I have two guesses.

It is an LED that is associated with a GPIO button (KEYBOARD_GPIO) such as the NumLock key on a keyboard. When the NumLock key is pressed then the LED will toggle on/off.
If this is correct the why not just use:

leds {
  pinctrl-names = "default";
  pinctrl-0 = <&user_leds_s0>;
  compatible = "gpio-leds";
  led1 {
    label = "board:green:led";
    gpios = <&gpio1 23 GPIO_ACTIVE_LOW>;
    linux,default-trigger = "numlock";
    default-state = "off";
  };
}

It is an LED that is being used as input device. Search for ‘Using Light Emitting Diode Arrays as
Touch-Sensitive Input and Output Devices’.

What is the intended purpose of the kernel config setting ‘INPUT_LEDS’?

Thank you,

RobertCNelson · August 2, 2021, 5:53pm

github.com

torvalds/linux/blob/master/drivers/input/Kconfig#L28-L39


      
          config INPUT_LEDS
          	tristate "Export input device LEDs in sysfs"
          	depends on LEDS_CLASS
          	default INPUT
          	help
          	  Say Y here if you would like to export LEDs on input devices
          	  as standard LED class devices in sysfs.
          
          	  If unsure, say Y.
          
          	  To compile this driver as a module, choose M here: the
          	  module will be called input-leds.

Say Y here if you would like to export LEDs on input devices as standard LED class devices in sysfs.

Think LED’s on keyboard, mice, etc… aka “input” devices…

Regards,