[PATCH] x86_64 genapic update

x86_64 genapic mechanism should be aware of machines that use physical APIC
mode regardless of how many clusters/processors are detected.

ACPI 3.0 FADT makes this determination very simple by providing a feature
flag "force_apic_physical_destination_mode" to state whether the machine
unconditionally uses physical APIC mode.

Unisys' next generation x86_64 ES7000 will need to utilize this FADT
feature flag in order to boot the x86_64 kernel in the correct APIC mode. 
This patch has been tested on both x86_64 commodity and ES7000 boxes.

Signed-off-by: Jason Davis <jason.davis@unisys.com>
Acked-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/arch/x86_64/kernel/genapic.c b/arch/x86_64/kernel/genapic.c
index d2c42fb99cb3..69b9c25a8fc4 100644
--- a/arch/x86_64/kernel/genapic.c
+++ b/arch/x86_64/kernel/genapic.c
@@ -20,6 +20,10 @@
 #include <asm/smp.h>
 #include <asm/ipi.h>
 
+#if defined(CONFIG_ACPI_BUS)
+#include <acpi/acpi_bus.h>
+#endif
+
 /* which logical CPU number maps to which CPU (physical APIC ID) */
 u8 x86_cpu_to_apicid[NR_CPUS] = { [0 ... NR_CPUS-1] = BAD_APICID };
 EXPORT_SYMBOL(x86_cpu_to_apicid);
@@ -47,6 +51,18 @@ void __init clustered_apic_check(void)
                 goto print;
         }
 
+#if defined(CONFIG_ACPI_BUS)
+        /*
+         * Some x86_64 machines use physical APIC mode regardless of how many
+         * procs/clusters are present (x86_64 ES7000 is an example).
+         */
+        if (acpi_fadt.revision > FADT2_REVISION_ID)
+                if (acpi_fadt.force_apic_physical_destination_mode) {
+                        genapic = &apic_cluster;
+                        goto print;
+                }
+#endif
+
         memset(cluster_cnt, 0, sizeof(cluster_cnt));
 
         for (i = 0; i < NR_CPUS; i++) {