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-rw-r--r--Documentation/input/event-codes.txt13
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diff --git a/Documentation/input/event-codes.txt b/Documentation/input/event-codes.txt
index f1ea2c69648d..c587a966413e 100644
--- a/Documentation/input/event-codes.txt
+++ b/Documentation/input/event-codes.txt
@@ -281,6 +281,19 @@ gestures can normally be extracted from it.
If INPUT_PROP_SEMI_MT is not set, the device is assumed to be a true MT
device.
+INPUT_PROP_TOPBUTTONPAD:
+-----------------------
+Some laptops, most notably the Lenovo *40 series provide a trackstick
+device but do not have physical buttons associated with the trackstick
+device. Instead, the top area of the touchpad is marked to show
+visual/haptic areas for left, middle, right buttons intended to be used
+with the trackstick.
+
+If INPUT_PROP_TOPBUTTONPAD is set, userspace should emulate buttons
+accordingly. This property does not affect kernel behavior.
+The kernel does not provide button emulation for such devices but treats
+them as any other INPUT_PROP_BUTTONPAD device.
+
Guidelines:
==========
The guidelines below ensure proper single-touch and multi-finger functionality.