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+What: /sys/class/leds/<led>/pattern
+Date: September 2018
+KernelVersion: 4.20
+Description:
+ Specify a software pattern for the LED, that supports altering
+ the brightness for the specified duration with one software
+ timer. It can do gradual dimming and step change of brightness.
+
+ The pattern is given by a series of tuples, of brightness and
+ duration (ms). The LED is expected to traverse the series and
+ each brightness value for the specified duration. Duration of
+ 0 means brightness should immediately change to new value, and
+ writing malformed pattern deactivates any active one.
+
+ 1. For gradual dimming, the dimming interval now is set as 50
+ milliseconds. So the tuple with duration less than dimming
+ interval (50ms) is treated as a step change of brightness,
+ i.e. the subsequent brightness will be applied without adding
+ intervening dimming intervals.
+
+ The gradual dimming format of the software pattern values should be:
+ "brightness_1 duration_1 brightness_2 duration_2 brightness_3
+ duration_3 ...". For example:
+
+ echo 0 1000 255 2000 > pattern
+
+ It will make the LED go gradually from zero-intensity to max (255)
+ intensity in 1000 milliseconds, then back to zero intensity in 2000
+ milliseconds:
+
+ LED brightness
+ ^
+ 255-| / \ / \ /
+ | / \ / \ /
+ | / \ / \ /
+ | / \ / \ /
+ 0-| / \/ \/
+ +---0----1----2----3----4----5----6------------> time (s)
+
+ 2. To make the LED go instantly from one brigntess value to another,
+ we should use use zero-time lengths (the brightness must be same as
+ the previous tuple's). So the format should be:
+ "brightness_1 duration_1 brightness_1 0 brightness_2 duration_2
+ brightness_2 0 ...". For example:
+
+ echo 0 1000 0 0 255 2000 255 0 > pattern
+
+ It will make the LED stay off for one second, then stay at max brightness
+ for two seconds:
+
+ LED brightness
+ ^
+ 255-| +---------+ +---------+
+ | | | | |
+ | | | | |
+ | | | | |
+ 0-| -----+ +----+ +----
+ +---0----1----2----3----4----5----6------------> time (s)
+
+What: /sys/class/leds/<led>/hw_pattern
+Date: September 2018
+KernelVersion: 4.20
+Description:
+ Specify a hardware pattern for the LED, for LED hardware that
+ supports autonomously controlling brightness over time, according
+ to some preprogrammed hardware patterns. It deactivates any active
+ software pattern.
+
+ Since different LED hardware can have different semantics of
+ hardware patterns, each driver is expected to provide its own
+ description for the hardware patterns in their ABI documentation
+ file.
+
+What: /sys/class/leds/<led>/repeat
+Date: September 2018
+KernelVersion: 4.20
+Description:
+ Specify a pattern repeat number. -1 means repeat indefinitely,
+ other negative numbers and number 0 are invalid.
+
+ This file will always return the originally written repeat
+ number.