[PATCH] Do not enforce unique IO_APIC_ID check for xAPIC systems (i386)

This patch is per Andi's request to remove NO_IOAPIC_CHECK from genapic and
use heuristics to prevent unique I/O APIC ID check for systems that don't
need it.  The patch disables unique I/O APIC ID check for Xeon-based and
other platforms that don't use serial APIC bus for interrupt delivery.
Andi stated that AMD systems don't need unique IO_APIC_IDs either.

Signed-off-by: Natalie Protasevich <Natalie.Protasevich@unisys.com>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 10 insertions, 5 deletions

diff --git a/arch/i386/kernel/io_apic.c b/arch/i386/kernel/io_apic.c
index 7a324e8b86f9..51f7a5d8721f 100644
--- a/arch/i386/kernel/io_apic.c
+++ b/arch/i386/kernel/io_apic.c
@@ -1659,6 +1659,12 @@ static void __init setup_ioapic_ids_from_mpc(void)
         unsigned long flags;
 
         /*
+         * Don't check I/O APIC IDs for xAPIC systems.  They have
+         * no meaning without the serial APIC bus.
+         */
+        if (!(boot_cpu_data.x86_vendor == X86_VENDOR_INTEL && boot_cpu_data.x86 < 15))
+                return;
+        /*
          * This is broken; anything with a real cpu count has to
          * circumvent this idiocy regardless.
          */
@@ -1684,10 +1690,6 @@ static void __init setup_ioapic_ids_from_mpc(void)
                         mp_ioapics[apic].mpc_apicid = reg_00.bits.ID;
                 }
 
-                /* Don't check I/O APIC IDs for some xAPIC systems.  They have
-                 * no meaning without the serial APIC bus. */
-                if (NO_IOAPIC_CHECK)
-                        continue;
                 /*
                  * Sanity check, is the ID really free? Every APIC in a
                  * system must have a unique ID or we get lots of nice
diff --git a/arch/i386/kernel/mpparse.c b/arch/i386/kernel/mpparse.c
index 1347ab4939e7..0a061056b828 100644
--- a/arch/i386/kernel/mpparse.c
+++ b/arch/i386/kernel/mpparse.c
@@ -914,7 +914,10 @@ void __init mp_register_ioapic (
         mp_ioapics[idx].mpc_apicaddr = address;
 
         set_fixmap_nocache(FIX_IO_APIC_BASE_0 + idx, address);
-        mp_ioapics[idx].mpc_apicid = io_apic_get_unique_id(idx, id);
+        if ((boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) && (boot_cpu_data.x86 < 15))
+                mp_ioapics[idx].mpc_apicid = io_apic_get_unique_id(idx, id);
+        else
+                mp_ioapics[idx].mpc_apicid = id;
         mp_ioapics[idx].mpc_apicver = io_apic_get_version(idx);
         
         /*