[PATCH] x86: make CONFIG_HOTPLUG_CPU depend on !X86_PC

[PATCH] x86: make CONFIG_HOTPLUG_CPU depend on !X86_PC

Make CONFIG_HOTPLUG_CPU depend on !X86_PC, so we need to turn on either
CONFIG_GENERICARCH, CONFIG_BIGSMP or any other subarch except X86_PC when
CONFIG_HOTPLUG_CPU=y

With 2.6.15+ kernels when CONFIG_HOTPLUG_CPU is turned on we switch to
bigsmp mode for sending IPI's and ioapic configurations that caused the
following error message.

>> More than 8 CPUs detected and CONFIG_X86_PC cannot handle it.
>> Use CONFIG_X86_GENERICARCH or CONFIG_X86_BIGSMP.

Originally bigsmp was added just to handle >8 cpus, but now with hotplug
cpu support we need to use bigsmp mode (why?  see below), that cause the
above error message even if there were less than 8 cpus in the system.

The message is bogus, but we are cannot use logical flat mode due to issues
with broadcast IPI can confuse a CPU just comming up.  We use flat physical
mode just like x86_64 case.  More details on why bigsmp now uses flat
physical mode (vs.  cluster mode) in following link.

http://marc.theaimsgroup.com/?l=linux-kernel&m=113261865814107&w=2

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>