USB prevents system from powering off and ucom prevents usb from being unloaded - ideas?

Michael Nottebrock lofi at
Wed Jan 16 09:38:45 PST 2008

Subject line is the executive summary of my problem:

I have a box with an Intel 945GC A2 chipset that will not poweroff on shutdown 
if the usb kernel module is loaded (or statically compiled into the kernel). 
Unloading the usb kernel modules sometime during shutdown (I hacked the usbd 
rc script for this) to work around the problem helped until I needed to hook 
up another device which uses ucom(4) to the machine. On kldunload, ucom 
claims to detach, but remains loaded and subsequent kldunload attempts 
trigger the error "kldunload: attempt to unload file that was loaded by the 
kernel". The stuck ucom in turn prevents usb from getting unloaded and the 
machine cannot poweroff.

I have already tried disabling EHCI, but it does not help. Any ideas on either 
getting uhci to properly detach on shutdown or getting rid of ucom?

   ,_,   | Michael Nottebrock               | lofi at
 (/^ ^\) | FreeBSD - The Power to Serve     |
   \u/   | K Desktop Environment on FreeBSD |
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