leds: add oneshot trigger

Add oneshot trigger to blink a led with configurale parameters via
sysfs.

Signed-off-by: Fabio Baltieri <fabio.baltieri@gmail.com>
Cc: Shuah Khan <shuahkhan@gmail.com>
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>

1 files changed, 59 insertions, 0 deletions

diff --git a/Documentation/leds/ledtrig-oneshot.txt b/Documentation/leds/ledtrig-oneshot.txt
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index 000000000000..07cd1fa41a3a
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+++ b/Documentation/leds/ledtrig-oneshot.txt
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+One-shot LED Trigger
+====================
+
+This is a LED trigger useful for signaling the user of an event where there are
+no clear trap points to put standard led-on and led-off settings.  Using this
+trigger, the application needs only to signal the trigger when an event has
+happened, than the trigger turns the LED on and than keeps it off for a
+specified amount of time.
+
+This trigger is meant to be usable both for sporadic and dense events.  In the
+first case, the trigger produces a clear single controlled blink for each
+event, while in the latter it keeps blinking at constant rate, as to signal
+that the events are arriving continuously.
+
+A one-shot LED only stays in a constant state when there are no events.  An
+additional "invert" property specifies if the LED has to stay off (normal) or
+on (inverted) when not rearmed.
+
+The trigger can be activated from user space on led class devices as shown
+below:
+
+  echo oneshot > trigger
+
+This adds the following sysfs attributes to the LED:
+
+  delay_on - specifies for how many milliseconds the LED has to stay at
+             LED_FULL brightness after it has been armed.
+             Default to 100 ms.
+
+  delay_off - specifies for how many milliseconds the LED has to stay at
+              LED_OFF brightness after it has been armed.
+              Default to 100 ms.
+
+  invert - reverse the blink logic.  If set to 0 (default) blink on for delay_on
+           ms, then blink off for delay_off ms, leaving the LED normally off.  If
+           set to 1, blink off for delay_off ms, then blink on for delay_on ms,
+           leaving the LED normally on.
+           Setting this value also immediately change the LED state.
+
+  shot - write any non-empty string to signal an events, this starts a blink
+         sequence if not already running.
+
+Example use-case: network devices, initialization:
+
+  echo oneshot > trigger # set trigger for this led
+  echo 33 > delay_on     # blink at 1 / (33 + 33) Hz on continuous traffic
+  echo 33 > delay_off
+
+interface goes up:
+
+  echo 1 > invert # set led as normally-on, turn the led on
+
+packet received/transmitted:
+
+  echo 1 > shot # led starts blinking, ignored if already blinking
+
+interface goes down
+
+  echo 0 > invert # set led as normally-off, turn the led off