[PATCH] x86_64: Only do the clustered systems have unsynchronized TSC assumption on IBM systems

Big Unisys systems have multiple clusters too, but they have an
synchronized TSC.

I'm using the SMBIOS to check for vendor == IBM.

Cc: Chris McDermott <lcm@us.ibm.com>
Cc: "Protasevich, Natalie" <Natalie.Protasevich@unisys.com>

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 8 insertions, 4 deletions

diff --git a/arch/i386/kernel/acpi/boot.c b/arch/i386/kernel/acpi/boot.c
index 79577f0ace98..8309a7b2cd63 100644
--- a/arch/i386/kernel/acpi/boot.c
+++ b/arch/i386/kernel/acpi/boot.c
@@ -44,9 +44,6 @@ extern void __init clustered_apic_check(void);
 extern int gsi_irq_sharing(int gsi);
 #include <asm/proto.h>
 
-static inline int acpi_madt_oem_check(char *oem_id, char *oem_table_id) { return 0; }
-
-
 #else                           /* X86 */
 
 #ifdef  CONFIG_X86_LOCAL_APIC
diff --git a/arch/x86_64/kernel/apic.c b/arch/x86_64/kernel/apic.c
index e5b14c57eaa0..d70605eda333 100644
--- a/arch/x86_64/kernel/apic.c
+++ b/arch/x86_64/kernel/apic.c
@@ -962,12 +962,14 @@ void smp_apic_timer_interrupt(struct pt_regs *regs)
         irq_exit();
 }
 
+int __initdata unsync_tsc_on_multicluster;
+
 /*
  * oem_force_hpet_timer -- force HPET mode for some boxes.
  *
  * Thus far, the major user of this is IBM's Summit2 series:
  *
- * Clustered boxes may have unsynced TSC problems if they are
+ * Some clustered boxes may have unsynced TSC problems if they are
  * multi-chassis. Use available data to take a good guess.
  * If in doubt, go HPET.
  */
@@ -977,6 +979,11 @@ __cpuinit int oem_force_hpet_timer(void)
         unsigned id;
         DECLARE_BITMAP(clustermap, NUM_APIC_CLUSTERS);
 
+        /* Only do this check on IBM machines - big Unisys systems
+           use multiple clusters too, but have synchronized TSC */
+        if (!unsync_tsc_on_multicluster)
+                return 0;
+
         bitmap_zero(clustermap, NUM_APIC_CLUSTERS);
 
         for (i = 0; i < NR_CPUS; i++) {