Last week I sent this same question to the openipmi-developer list on 
sourceforge, but did not get any replies.
Does anyone here know the answer?

========
AFAICT my system does not support ipmi, but despite that fact something is 
loading the ipmi_msghandler module and trying to load the ipmi_si module.

The second fails, but the first stays loaded. From dmesg:
ipmi message handler version 39.1
[...]
ipmi_si: Trying PCI-specified kcs state machine at mem address 0x90220000, 
slave address 0x0, irq 19
ipmi_si: There appears to be no BMC at this location
ipmi_si: Unable to find any System Interface(s)

This results in powertop showing:
   Top causes for wakeups:
   [...]
      2.1% ( 10.0)   <kernel module> : ipmi_init_msghandler (ipmi_timeout)

AFAICT from modules.pcimap, ipmi_si should only be loaded for PCI ID 
[103c:121a] (which I don't have), or for devices with class c0700 (which I 
also don't have).
I also cannot find anything in /etc that could be responsible.

So I wonder what _is_ responsible for trying to load the ipmi modules on my 
system and if that shouldn't be avoided.

My system is Debian testing running 2.6.23.

Cheers,
Frans Pop