From: mikep@csd.uu.se

There has been a number of problem reports about local APIC
interacting badly with ACPI on P4s due to the P4 local APIC
force-enable change in 2.5.74,

This patch reverts the 2.5.74 patch, so if the BIOS disables
the local APIC on a P4, we don't enable it by default any more.

The rescue the situation for those P4 systems where the local
APIC _can_ be enabled safely, I've added two kernel parameters
that can be used to override broken BIOSen:
- "nolapic" prevents the kernel from enabling or using the local
  APIC. This is stronger than listing a machine in the DMI scan
  blacklist, since it also works for machines that boot with the
  local APIC already enabled.
- "lapic" tells the kernel to force-enable the P4 local APIC if
  the BIOS disabled it. I haven't changed the logic for P6/K7
  family processors, so we still force-enable those unless
  "nolapic" was passed to the kernel.

The patch also includes a cleanup: the dont_use_local_apic_timer
flag variable is not set any more since 2.5.74, so it's removed.