immediately, back off to the next higher Cx sleep state. Some machines
with a Via chipset report a valid C3 but a register read doesn't actually
halt the CPU. This would cause the machine to appear unresponsive as it
repeatedly called cpu_idle() which immediately returned. Causing interrupts
(i.e. by pressing the power button) would cause the system to make forward
progress, showing that it wasn't actually hung.
Also, enable interrupts a little earlier. We don't need them disabled
to calculate the delta time for the read.
Reported by: silby
MFC after: 2 weeks
80f006a1e3