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Date:	Wed, 20 Jan 2010 20:15:31 -0800
From:	Greg KH <>
	Suresh Siddha <>,
	Chris McDermott <>,
	Yinghai Lu <>
Subject: [10/30] x86, apic: use physical mode for IBM summit platforms

2.6.32-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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