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dt-bindings: leds: Add pattern initialization from Device Tree

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Document new led-pattern property for initialization of LED triggers.
The property format is trigger-specific (except being array of
integers).  For pattern trigger, the explanation of pattern format was
moved to a common file shared with sysfs ABI.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
This commit is contained in:
Krzysztof Kozlowski 2019-01-09 15:44:45 +01:00 committed by Jacek Anaszewski
parent bfeffd1552
commit 1dd7093742
3 changed files with 64 additions and 48 deletions
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51
Documentation/ABI/testing/sysfs-class-led-trigger-pattern
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@ -7,55 +7,10 @@ Description:
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.
duration (ms).
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 brightness value to another,
we should 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)
The exact format is described in:
Documentation/devicetree/bindings/leds/leds-trigger-pattern.txt
What: /sys/class/leds/<led>/hw_pattern
Date: September 2018

12
Documentation/devicetree/bindings/leds/common.txt
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@ -37,6 +37,18 @@ Optional properties for child nodes:
"ide-disk" - LED indicates IDE disk activity (deprecated),
in new implementations use "disk-activity"
"timer" - LED flashes at a fixed, configurable rate
"pattern" - LED alters the brightness for the specified duration with one
software timer (requires "led-pattern" property)
- led-pattern : Array of integers with default pattern for certain triggers.
Each trigger may parse this property differently:
- one-shot : two numbers specifying delay on and delay off (in ms),
- timer : two numbers specifying delay on and delay off (in ms),
- pattern : the pattern is given by a series of tuples, of
brightness and duration (in ms). The exact format is
described in:
Documentation/devicetree/bindings/leds/leds-trigger-pattern.txt
- led-max-microamp : Maximum LED supply current in microamperes. This property
can be made mandatory for the board configurations

49
Documentation/devicetree/bindings/leds/leds-trigger-pattern.txt Normal file
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@ -0,0 +1,49 @@
* Pattern format for LED pattern trigger
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 (using sysfs interface):
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 brightness value to another, we should
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 (using sysfs interface):
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)