ACPI: Add support to parse 2nd MADT

When a BIOS bug presents multiple APIC/MADTs,
Linux currently uses the 1st and ignores the 2nd.

But some machines work better if we use the 2nd.

http://bugzilla.kernel.org/show_bug.cgi?id=7465

Add a warning and boot parameter "acpi_apic_instance=2"
to allow parsing the 2nd.

No change to default behaviour in this patch.

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

1 files changed, 6 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 856c8b114e71..22c6b8ccaea5 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -138,6 +138,12 @@ and is between 256 and 4096 characters. It is defined in the file
 
                         See also Documentation/pm.txt, pci=noacpi
 
+        acpi_apic_instance=     [ACPI, IOAPIC]
+                        Format: <int>
+                        2: use 2nd APIC table, if available
+                        1,0: use 1st APIC table
+                        default: 0
+
         acpi_sleep=     [HW,ACPI] Sleep options
                         Format: { s3_bios, s3_mode }
                         See Documentation/power/video.txt