My laptop is Toshiba M840. When I suspend, my laptop auto resumes immediately. I used
acpitool to check what devices made my computer waking up. After I disable the XHC, my computer suspends properly. But after restart, the XHC was enabled.
How can I disable it forever?
You can try to disable it with a Upstart script every startup automatically:
Create a file
start on started dbus stop on stopping dbus script sudo -u root sh -c "echo 'XHC' > /proc/acpi/wakeup" end script