Comment 325 for bug 88746

I wonder if it could be something to do specifically with USB-connected HDD's, since my other devices work just fine? The controller in the drive/enclosure, perhaps? I wouldn't know where to start to look there.

I tried what Toby tried as well, without success:
I had never tried actually disabling autosuspend, only unloading ehci-hcd. I applied the usbcore autosuspend module option to a file in modprobe.d/, rebuilt my initramfs, and shut down. On reboot, I tried investigating the contents of

find /sys/ -name "autosuspend" && cat `find /sys/ -name "autosuspend"`

on my system. All reported -1, which is autosuspend off (as was set by the usbcore module option). However, on access to my USB external hdd, the same symptoms occur - all usb activity halts. My mouse and keyboard fail to respond, and the machine they are connected to must be rebooted to bring them back up - a simple rmmod/modprobe combo doesn't do the trick to re-enable them.

If I unload the ehci-hcd module, everything is as it was before I tried the fix. I can use my mouse, keyboard, and external hdd.