Answering my own mail:

> I tried a call to
> apm_powmgt_enable(1);
> (which is #ifdef'd out in the current driver)
> 
> This gives:
> APM power management enable <apmbios enable>:unrecognized device ID (9)

There is a bug in apm_powmgt_enable(1):
It passes APM_DEV_APM_BIOS as device specification, if
version 1.1 is active. (apm.c, line 476)
The correct value is APM_DEV_ALLDEVS.

Behaves much better now, no error messages anymore.
(Still strange: the suspend button works only once after a boot.)

best regards
Matthias Drochner