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-rw-r--r--Documentation/input/event-codes.rst15
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diff --git a/Documentation/input/event-codes.rst b/Documentation/input/event-codes.rst
index b24b5343f5eb..3118fc1c1e26 100644
--- a/Documentation/input/event-codes.rst
+++ b/Documentation/input/event-codes.rst
@@ -236,6 +236,21 @@ A few EV_ABS codes have special meanings:
- Used to describe multitouch input events. Please see
multi-touch-protocol.txt for details.
+* ABS_PRESSURE/ABS_MT_PRESSURE:
+
+ - For touch devices, many devices converted contact size into pressure.
+ A finger flattens with pressure, causing a larger contact area and thus
+ pressure and contact size are directly related. This is not the case
+ for other devices, for example digitizers and touchpads with a true
+ pressure sensor ("pressure pads").
+
+ A device should set the resolution of the axis to indicate whether the
+ pressure is in measurable units. If the resolution is zero, the
+ pressure data is in arbitrary units. If the resolution is nonzero, the
+ pressure data is in units/gram. For example, a value of 10 with a
+ resolution of 1 represents 10 gram, a value of 10 with a resolution on
+ 1000 represents 10 microgram.
+
EV_SW
-----