Linux tells ICH4 users that they can (manually) invoke
"hpet=force" to enable the undocumented ICH-4M HPET.
The HPET becomes available for both clocksource and clockevents.
But as of ff69f2bba6
(acpi: fix of pmtimer overflow that make Cx states time incorrect)
the HPET may be used via clocksource for idle accounting, and
hpet=force on an ICH4 box hangs boot.
It turns out that touching the MMIO HPET withing
the ARB_DIS part of C3 will hang the hardware.
The fix is to simply move the timer access outside
the ARB_DIS region. This is a no-op on modern hardware
because ARB_DIS is no longer used.
http://bugzilla.kernel.org/show_bug.cgi?id=13087
Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
f461ddea0a