While I'm thinking of it, in the my last alps driver dkms, I put in an
ACPI interface to uniquely detect the touchpad type. After spending a
good couple of days figuring out the ACPI spec and this mysterious _HID
(hardware id) and _CID (compatibility id) as it relates to how ALPS
identifies its touchpads, I can confirm Linus' quote "ACPI is a complete
design disaster in every way. But we're kind of stuck with it." Some
ALPS touchpads have different _HID values. Some have the same _HID but
different behavior.
As far as I can tell ACPI has varying degrees of usefulness based on the
h/w manufacturer. The ALPS MS Windows drivers appear to use ACPI to
figure out if the touchpad is, in fact, from ALPS and then a complicated
series of proprietary retrievals to figure out the behavior.
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