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-rw-r--r--Documentation/input/event-codes.txt11
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diff --git a/Documentation/input/event-codes.txt b/Documentation/input/event-codes.txt
index 53305bd..f1ea2c6 100644
--- a/Documentation/input/event-codes.txt
+++ b/Documentation/input/event-codes.txt
@@ -196,6 +196,17 @@ EV_MSC:
EV_MSC events are used for input and output events that do not fall under other
categories.
+A few EV_MSC codes have special meaning:
+
+* MSC_TIMESTAMP:
+ - Used to report the number of microseconds since the last reset. This event
+ should be coded as an uint32 value, which is allowed to wrap around with
+ no special consequence. It is assumed that the time difference between two
+ consecutive events is reliable on a reasonable time scale (hours).
+ A reset to zero can happen, in which case the time since the last event is
+ unknown. If the device does not provide this information, the driver must
+ not provide it to user space.
+
EV_LED:
----------
EV_LED events are used for input and output to set and query the state of