ACPI: disable MPS when NO APIC-table found

When ACPI is asked to find an MADT (APIC table)
and fails, then ACPI expects to run in PIC mode.

However, if an MP Table is was found, IRQs will be
registered as if an IOAPIC is being used, even
though ACPI is configuring interrupt links links for PIC mode.

In this scenario, disable MPS so that IRQs
are registered in PIC mode, consistent with ACPI.

http://bugzilla.kernel.org/show_bug.cgi?id=12257

Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 4c51a2f8fd31..de8ce79dd881 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -1359,6 +1359,17 @@ static void __init acpi_process_madt(void)
                                "Invalid BIOS MADT, disabling ACPI\n");
                         disable_acpi();
                 }
+        } else {
+                /*
+                 * ACPI found no MADT, and so ACPI wants UP PIC mode.
+                 * In the event an MPS table was found, forget it.
+                 * Boot with "acpi=off" to use MPS on such a system.
+                 */
+                if (smp_found_config) {
+                        printk(KERN_WARNING PREFIX
+                                "No APIC-table, disabling MPS\n");
+                        smp_found_config = 0;
+                }
         }
 #endif
         return;