linux/Documentation/leds/well-known-leds.txt

-*- org -*-

It is somehow important to provide consistent interface to the
userland. LED devices have one problem there, and that is naming of
directories in /sys/class/leds. It would be nice if userland would
just know right "name" for given LED function, but situation got more
complex.

Anyway, if backwards compatibility is not an issue, new code should
use one of the "good" names from this list, and you should extend the
list where applicable.

Legacy names are listed, too; in case you are writing application that
wants to use particular feature, you should probe for good name, first,
but then try the legacy ones, too.

Notice there's a list of functions in include/dt-bindings/leds/common.h .

* Gamepads and joysticks

Game controllers may feature LEDs to indicate a player number. This is commonly
used on game consoles in which multiple controllers can be connected to a system.
The "player LEDs" are then programmed with a pattern to indicate a particular
player. For example, a game controller with 4 LEDs, may be programmed with "x---"
to indicate player 1, "-x--" to indicate player 2 etcetera where "x" means on.
Input drivers can utilize the LED class to expose the individual player LEDs
of a game controller using the function "player".
Note: tracking and management of Player IDs is the responsibility of user space,
though drivers may pick a default value.

Good: "input*:*:player-{1,2,3,4,5}

* Keyboards
  
Good: "input*:*:capslock"
Good: "input*:*:scrolllock"
Good: "input*:*:numlock"
Legacy: "shift-key-light" (Motorola Droid 4, capslock)

Set of common keyboard LEDs, going back to PC AT or so.

Legacy: "tpacpi::thinklight" (IBM/Lenovo Thinkpads)
Legacy: "lp5523:kb{1,2,3,4,5,6}" (Nokia N900)

Frontlight/backlight of main keyboard.

Legacy: "button-backlight" (Motorola Droid 4)

Some phones have touch buttons below screen; it is different from main
keyboard. And this is their backlight.

* Sound subsystem

Good: "platform:*:mute"
Good: "platform:*:micmute"

LEDs on notebook body, indicating that sound input / output is muted.

* System notification

Legacy: "status-led:{red,green,blue}" (Motorola Droid 4)
Legacy: "lp5523:{r,g,b}" (Nokia N900)

Phones usually have multi-color status LED.

* Power management

Good: "platform:*:charging" (allwinner sun50i)

* Screen

Good: ":backlight" (Motorola Droid 4)