I'm not sure whether this strictly belongs under Hardware, but I can't see any better place to put it...
When I load the uhci_hcd module with no USB devices plugged in, or if I unplug all devices with the module loaded, my system hangs.
It is fine if I have any USB 1 device plugged in (I don't have any USB 2 ones to try), only when there are none connected is there a problem.
ehci_hcd has no problems at all, although, as said before, I don't have any USB 2 devices, and ehci_hcd does not detect USB 1 devs.
I have tried loading uhci_hcd both with and without ehci_hcd already loaded, and with "legacy USB" both on and off in my BIOS.
This problem has happened on various distros, although I have only been able to investigate it properly on my main Gentoo system.
I have tried many kernels from 2.6.11 to 2.6.12, both vanilla and with Gentoo patches, and other distros using those kernels also
hang unless I plug a USB device in. I did not have the problem with kernel 2.6.10. The ports are USB2 ones.
I have managed to capture a log of the crash, using the USB debug option, and putting an endless loop of sync commands after the command to load the uhci_hcd module, in order to get the logs onto the hard drive before the system hung (I did confirm on the console that the log I got had everything that was produced there, with dmesg -n 8). This logged run was with no USB modules loaded beforehand and no USB devices plugged in.
uname -a output:
Linux sodashark 2.6.12-gentoo #2 Mon Jun 20 19:40:08 BST 2005 i686 Intel(R) Pentium(R) M processor 1500MHz GenuineIntel GNU/Linux
URLs with information on problem (all of these are plain text files with DOS EOL):
Latest info on problem - http://www.chrise.me.uk/dump/uhci_crash.txt
System log from module load to hang - http://www.chrise.me.uk/dump/uhci_crash_log.txt
Kernel config file - http://www.chrise.me.uk/dump/uhci_crash_config.txt