I'm using debian testing, 2.6.32-5-amd64 on acer aspire 5520g and i had this error
hub 4-0:1.0: unable to enumerate USB device on port 2 so i did modprobe -r ehci_hcd and now i have hub 2-0:1.0: unable to enumerate USB device on port 6.
dmesg show me this error in loop, the performace of this laptop are really compromised