Documentation/ABI/testing/sysfs-class-led-trigger-pattern

   1 What:           /sys/class/leds/<led>/pattern
   2 Date:           September 2018
   3 KernelVersion:  4.20
   4 Description:
   5                 Specify a software pattern for the LED, that supports altering
   6                 the brightness for the specified duration with one software
   7                 timer. It can do gradual dimming and step change of brightness.
   8
   9                 The pattern is given by a series of tuples, of brightness and
  10                 duration (ms). The LED is expected to traverse the series and
  11                 each brightness value for the specified duration. Duration of
  12                 0 means brightness should immediately change to new value, and
  13                 writing malformed pattern deactivates any active one.
  14
  15                 1. For gradual dimming, the dimming interval now is set as 50
  16                 milliseconds. So the tuple with duration less than dimming
  17                 interval (50ms) is treated as a step change of brightness,
  18                 i.e. the subsequent brightness will be applied without adding
  19                 intervening dimming intervals.
  20
  21                 The gradual dimming format of the software pattern values should be:
  22                 "brightness_1 duration_1 brightness_2 duration_2 brightness_3
  23                 duration_3 ...". For example:
  24
  25                 echo 0 1000 255 2000 > pattern
  26
  27                 It will make the LED go gradually from zero-intensity to max (255)
  28                 intensity in 1000 milliseconds, then back to zero intensity in 2000
  29                 milliseconds:
  30
  31                 LED brightness
  32                     ^
  33                 255-|       / \            / \            /
  34                     |      /    \         /    \         /
  35                     |     /       \      /       \      /
  36                     |    /          \   /          \   /
  37                   0-|   /             \/             \/
  38                     +---0----1----2----3----4----5----6------------> time (s)
  39
  40                 2. To make the LED go instantly from one brightness value to another,
  41                 we should use zero-time lengths (the brightness must be same as
  42                 the previous tuple's). So the format should be:
  43                 "brightness_1 duration_1 brightness_1 0 brightness_2 duration_2
  44                 brightness_2 0 ...". For example:
  45
  46                 echo 0 1000 0 0 255 2000 255 0 > pattern
  47
  48                 It will make the LED stay off for one second, then stay at max brightness
  49                 for two seconds:
  50
  51                 LED brightness
  52                     ^
  53                 255-|        +---------+    +---------+
  54                     |        |         |    |         |
  55                     |        |         |    |         |
  56                     |        |         |    |         |
  57                   0-|   -----+         +----+         +----
  58                     +---0----1----2----3----4----5----6------------> time (s)
  59
  60 What:           /sys/class/leds/<led>/hw_pattern
  61 Date:           September 2018
  62 KernelVersion:  4.20
  63 Description:
  64                 Specify a hardware pattern for the LED, for LED hardware that
  65                 supports autonomously controlling brightness over time, according
  66                 to some preprogrammed hardware patterns. It deactivates any active
  67                 software pattern.
  68
  69                 Since different LED hardware can have different semantics of
  70                 hardware patterns, each driver is expected to provide its own
  71                 description for the hardware patterns in their ABI documentation
  72                 file.
  73
  74 What:           /sys/class/leds/<led>/repeat
  75 Date:           September 2018
  76 KernelVersion:  4.20
  77 Description:
  78                 Specify a pattern repeat number. -1 means repeat indefinitely,
  79                 other negative numbers and number 0 are invalid.
  80
  81                 This file will always return the originally written repeat
  82                 number.