1.. SPDX-License-Identifier: GPL-2.0 2 3==================================== 4Multicolor LED handling under Linux 5==================================== 6 7Description 8=========== 9The multicolor class groups monochrome LEDs and allows controlling two 10aspects of the final combined color: hue and lightness. The former is 11controlled via the multi_intensity array file and the latter is controlled 12via brightness file. 13 14Multicolor Class Control 15======================== 16The multicolor class presents files that groups the colors as indexes in an 17array. These files are children under the LED parent node created by the 18led_class framework. The led_class framework is documented in led-class.rst 19within this documentation directory. 20 21Each colored LED will be indexed under the multi_* files. The order of the 22colors will be arbitrary. The multi_index file can be read to determine the 23color name to indexed value. 24 25The multi_index file is an array that contains the string list of the colors as 26they are defined in each multi_* array file. 27 28The multi_intensity is an array that can be read or written to for the 29individual color intensities. All elements within this array must be written in 30order for the color LED intensities to be updated. 31 32Directory Layout Example 33======================== 34root:/sys/class/leds/multicolor:status# ls -lR 35-rw-r--r-- 1 root root 4096 Oct 19 16:16 brightness 36-r--r--r-- 1 root root 4096 Oct 19 16:16 max_brightness 37-r--r--r-- 1 root root 4096 Oct 19 16:16 multi_index 38-rw-r--r-- 1 root root 4096 Oct 19 16:16 multi_intensity 39 40Multicolor Class Brightness Control 41=================================== 42The brightness level for each LED is calculated based on the color LED 43intensity setting divided by the global max_brightness setting multiplied by 44the requested brightness. 45 46led_brightness = brightness * multi_intensity/max_brightness 47 48Example: 49A user first writes the multi_intensity file with the brightness levels 50for each LED that are necessary to achieve a certain color output from a 51multicolor LED group. 52 53cat /sys/class/leds/multicolor:status/multi_index 54green blue red 55 56echo 43 226 138 > /sys/class/leds/multicolor:status/multi_intensity 57 58red - 59 intensity = 138 60 max_brightness = 255 61green - 62 intensity = 43 63 max_brightness = 255 64blue - 65 intensity = 226 66 max_brightness = 255 67 68The user can control the brightness of that multicolor LED group by writing the 69global 'brightness' control. Assuming a max_brightness of 255 the user 70may want to dim the LED color group to half. The user would write a value of 71128 to the global brightness file then the values written to each LED will be 72adjusted base on this value. 73 74cat /sys/class/leds/multicolor:status/max_brightness 75255 76echo 128 > /sys/class/leds/multicolor:status/brightness 77 78adjusted_red_value = 128 * 138/255 = 69 79adjusted_green_value = 128 * 43/255 = 21 80adjusted_blue_value = 128 * 226/255 = 113 81 82Reading the global brightness file will return the current brightness value of 83the color LED group. 84 85cat /sys/class/leds/multicolor:status/brightness 86128 87