[PATCH v8 2/9] documention: leds: Add multicolor class documentation

[Dan Murphy]

Add the support documentation on the multicolor LED framework.
This document defines the directores and file generated by the
multicolor framework.  It also documents usage.

Signed-off-by: Dan Murphy <dmurphy@xxxxxx>
---
 Documentation/leds/index.rst                 |  1 +
 Documentation/leds/leds-class-multicolor.rst | 91 ++++++++++++++++++++
 2 files changed, 92 insertions(+)
 create mode 100644 Documentation/leds/leds-class-multicolor.rst

diff --git a/Documentation/leds/index.rst b/Documentation/leds/index.rst
index 060f4e485897..bc70c6aa7138 100644
--- a/Documentation/leds/index.rst
+++ b/Documentation/leds/index.rst
@@ -9,6 +9,7 @@ LEDs
 
    leds-class
    leds-class-flash
+   leds-class-multicolor
    ledtrig-oneshot
    ledtrig-transient
    ledtrig-usbport
diff --git a/Documentation/leds/leds-class-multicolor.rst b/Documentation/leds/leds-class-multicolor.rst
new file mode 100644
index 000000000000..063c9a411a1d
--- /dev/null
+++ b/Documentation/leds/leds-class-multicolor.rst
@@ -0,0 +1,91 @@
+====================================
+Multi Color LED handling under Linux
+====================================
+
+Description
+===========
+There are varying monochrome LED colors available for application.  These
+LEDs can be used as a single use case LED or can be mixed with other color
+LEDs to produce the full spectrum of color.  Color LEDs that are grouped
+can be presented under a single LED node with individual color control.
+The multicolor class groups these LEDs and allows dynamically setting the value
+of a single LED or setting the intensity values of the LEDs in the group and
+updating the LEDs virtually simultaneously.
+
+Multicolor Class Control
+========================
+The multicolor class presents the LED groups under a directory called "colors".
+This directory is a child under the LED parent node created by the led_class
+framework.  The led_class framework is documented in led-class.rst within this
+documentation directory.
+
+Each colored LED will have two files created under the colors directory
+<led_color>_intensity and <led_color>_max_intensity. These files will contain
+one of LED_COLOR_ID_* definitions from the header
+include/dt-bindings/leds/common.h.
+
+Directory Layout Example
+========================
+root:/sys/class/leds/rgb:grouped_leds# ls -lR colors/
+-rw-rwxr-- 1 root root 4096 Jul 7 03:10 red_max_intensity
+--w--wx-w- 1 root root 4096 Jul 7 03:10 red_intensity
+-rw-rwxr-- 1 root root 4096 Jul 7 03:10 green_max_intensity
+--w--wx-w- 1 root root 4096 Jul 7 03:10 green_intensity
+-rw-rwxr-- 1 root root 4096 Jul 7 03:10 blue_max_intensity
+--w--wx-w- 1 root root 4096 Jul 7 03:10 blue_intensity
+
+Multicolor Class Brightness Control
+===================================
+The multiclor class framework will calculate each monochrome LEDs intensity.
+
+The brightness level for each LED is calculated based on the color LED
+intensity setting divided by the color LED max intensity setting multiplied by
+the requested value.
+
+led_brightness = requested_value * led_color_intensity/led_color_max_intensity
+
+Example:
+Three LEDs are present in the group as defined in "Directory Layout Example"
+within this document.
+
+A user first writes the color LED brightness file with the brightness level that
+is necessary to achieve a blueish violet output from the RGB LED group.
+
+echo 138 > /sys/class/leds/rgb:grouped_leds/red_intensity
+echo 43 > /sys/class/leds/rgb:grouped_leds/green_intensity
+echo 226 > /sys/class/leds/rgb:grouped_leds/blue_intensity
+
+red -
+	intensity = 138
+	max_intensity = 255
+green -
+	intensity = 43
+	max_intensity = 255
+blue -
+	intensity = 226
+	max_intensity = 255
+
+The user can control the brightness of that RGB group by writing the parent
+'brightness' control.  Assuming a parent max_brightness of 255 the user may want
+to dim the LED color group to half.  The user would write a value of 128 to the
+parent brightness file then the values written to each LED will be adjusted
+base on this value
+
+cat /sys/class/leds/rgb:grouped_leds/max_brightness
+255
+echo 128 > /sys/class/leds/rgb:grouped_leds/brightness
+
+adjusted_red_value = 128 * 138/255 = 69
+adjusted_green_value = 128 * 43/255 = 21
+adjusted_blue_value = 128 * 226/255 = 113
+
+Reading the parent brightness file will return the current brightness value of
+the color LED group.
+
+cat /sys/class/leds/rgb:grouped_leds/max_brightness
+255
+
+echo 128 > /sys/class/leds/rgb:grouped_leds/brightness
+
+cat /sys/class/leds/rgb:grouped_leds/max_brightness
+128
-- 
2.22.0.214.g8dca754b1e