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Subject[22/89] x86, apic: use physical mode for IBM summit platforms
2.6.31-stable review patch.  If anyone has any objections, please let us know.

From: Suresh Siddha <>

commit dfea91d5a7c795fd6f4e1a97489a98e4e767463e upstream.

Chris McDermott from IBM confirmed that hurricane chipset in IBM summit
platforms doesn't support logical flat mode. Irrespective of the other
things like apic_id's, total number of logical cpu's, Linux kernel
should default to physical mode for this system.

The 32-bit kernel does so using the OEM checks for the IBM summit
platform. Add a similar OEM platform check for the 64bit kernel too.

Otherwise the linux kernel boot can hang on this platform under certain
bios/platform settings.

Signed-off-by: Suresh Siddha <>
Tested-by: Ananth N Mavinakayanahalli <>
Cc: Chris McDermott <>
Cc: Yinghai Lu <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Greg Kroah-Hartman <>

arch/x86/kernel/apic/apic_flat_64.c | 5 +++++
1 file changed, 5 insertions(+)
--- a/arch/x86/kernel/apic/apic_flat_64.c
+++ b/arch/x86/kernel/apic/apic_flat_64.c
@@ -240,6 +240,11 @@ static int physflat_acpi_madt_oem_check(
printk(KERN_DEBUG "system APIC only can use physical flat");
return 1;
+ if (!strncmp(oem_id, "IBM", 3) && !strncmp(oem_table_id, "EXA", 3)) {
+ printk(KERN_DEBUG "IBM Summit detected, will use apic physical");
+ return 1;
+ }

return 0;

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