[patch 1/2] x86, apic: use physical mode for IBM summit platforms

[Suresh Siddha <suresh.b.siddha@intel.com>]

[-- Attachment #1: ibm_summit_oem_check_for_x64.patch --]
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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. 32bit 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 <suresh.b.siddha@intel.com>
Tested-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Chris McDermott <lcm@linux.vnet.ibm.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: stable@kernel.org
---
 arch/x86/kernel/apic/apic_flat_64.c |    5 +++++
 1 file changed, 5 insertions(+)

Index: tip/arch/x86/kernel/apic/apic_flat_64.c
===================================================================
--- tip.orig/arch/x86/kernel/apic/apic_flat_64.c
+++ tip/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;
+	}
 #endif
 
 	return 0;