Comment 62 for bug 282220

Without 'acpi_sleep=s4_nohwsig':

Resume from hibernate always fails if the AC power is unplugged at any point, even if no periferals are attached, wether or not there is a battery in the unit.

With 'acpi_sleep=s4_nohwsig':

Resume works even if AC power is unplugged but (this I found later) there is one case where resume from both suspend and hibernate fail: when I resume/hibernate while docked, it won't resume after undocked, wether or not there is a battery on the unit and wether or not there are any peripherals (one external monitor, network, AC power) attached to the UltraDock. The reverse case works fine, I can hibernate/suspend while undocked and resume once docked.

For now I settled for setting 'acpi_sleep=s4_nohwsig' and keeping a battery on the unit at all times, even when docked, so that I don't have to hibernate it to undock it. In previous experience, keeping Li-ion batteries on laptos while working 10-12 hour workdays plugged into AC has tended to burn my batteries in less than six months, but this one seems to be holding out OK.