psm(4) support for Elantech touchpads

[Vladimir Kondratyev]

Hello

Some time ago I bought Acer Aspire S7-191 ultrabook and was able to run 
FreeBSD on it.
However, builtin Elantech clickpad turned out to be almost unusable due 
to bad support of gestures in PS/2 mouse emulation mode. So I had to 
port OpenBSD Linux derived absolute mode driver and connect it to 
FreeBSD synaptics gesture processor.

Resulting patch for 11-CURRENT can be downloaded here: 
http://mail.cicgroup.ru/elantech-touchpad-r287559.diff

It still requires some work but I find it quite usable. It supports and 
was tested on hardware versions 2..4 Elantech touchpads (namely ASUS 
EEEPC 1015PN, ASUS K53E and Acer Aspire S7-191)

Usage:

cd /usr/src
fetch http://mail.cicgroup.ru/elantech-touchpad-r287559.diff
patch -p1 < elantech-touchpad-r287559.diff
make kernel
echo "hw.psm.elantech_support=1" >> /boot/loader.conf
reboot

You should see following boot messages if touchpad has been recognized 
by psm(4) driver:

psm0: <PS/2 Mouse> irq 12 on atkbdc0
psm0: [GIANT-LOCKED]
psm0: model Elantech Touchpad, device ID 0

Patch adds some sysctls under hw.psm.elantech node. They mean exactly 
the same as hw.psm.synaptics ones

Comments and suggestions are welcome.