ALPS Touchpad Protocol
----------------------

Introduction
------------

Currently the ALPS touchpad driver supports two protocol versions in use by
ALPS touchpads, the "old" and "new" protocol versions. Fundamentally these
differ only in the format of their event packets (in reality many features may
be found on new protocol devices that aren't found on the old protocol
devices, but these are handled transparently as feature differences rather
than protocol differences).

Detection
---------

All ALPS touchpads should respond to the "E6 report" command sequence:
E8-E6-E6-E6-E9. An ALPS touchpad should respond with either 00-00-0A or
00-00-64.

If the E6 report is successful, the touchpad model is identified using the "E7
report" sequence: E8-E7-E7-E7-E9. The response is the model signature and is
matched against known models in the alps_model_data_array.

Packet Format
-------------

In the following tables, the following notation us used.

 CAPITALS = stick, miniscules = touchpad

?'s can have different meanings on different models, such as wheel rotation,
extra buttons, stick buttons on a dualpoint, etc.

PS/2 packet format
------------------

 byte 0:  0    0 YSGN XSGN    1    M    R    L
 byte 1: X7   X6   X5   X4   X3   X2   X1   X0
 byte 2: Y7   Y6   Y5   Y4   Y3   Y2   Y1   Y0

Note that the device never signals overflow condition.

ALPS Absolute Mode - Old Format
-------------------------------

 byte 0:  1    0    0    0    1   x9   x8   x7
 byte 1:  0   x6   x5   x4   x3   x2   x1   x0
 byte 2:  0    ?    ?    l    r    ?  fin  ges
 byte 3:  0    ?    ?    ?    ?   y9   y8   y7
 byte 4:  0   y6   y5   y4   y3   y2   y1   y0
 byte 5:  0   z6   z5   z4   z3   z2   z1   z0

ALPS Absolute Mode - New Format
-------------------------------

 byte 0:  1    ?    ?    ?    1    ?    ?    ?
 byte 1:  0   x6   x5   x4   x3   x2   x1   x0
 byte 2:  0  x10   x9   x8   x7    ?  fin  ges
 byte 3:  0   y9   y8   y7    1    M    R    L
 byte 4:  0   y6   y5   y4   y3   y2   y1   y0
 byte 5:  0   z6   z5   z4   z3   z2   z1   z0

Dualpoint device -- interleaved packet format
---------------------------------------------

 byte 0:    1    1    0    0    1    1    1    1
 byte 1:    0   x6   x5   x4   x3   x2   x1   x0
 byte 2:    0  x10   x9   x8   x7    0  fin  ges
 byte 3:    0    0 YSGN XSGN    1    1    1    1
 byte 4:   X7   X6   X5   X4   X3   X2   X1   X0
 byte 5:   Y7   Y6   Y5   Y4   Y3   Y2   Y1   Y0
 byte 6:    0   y9   y8   y7    1    m    r    l
 byte 7:    0   y6   y5   y4   y3   y2   y1   y0
 byte 8:    0   z6   z5   z4   z3   z2   z1   z0