5 files changed, 10 insertions, 2 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index c9115c1b672c..136f02842de9 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -139,6 +139,7 @@ and is between 256 and 4096 characters. It is defined in the file
                         ht -- run only enough ACPI to enable Hyper Threading
                         strict -- Be less tolerant of platforms that are not
                                 strictly ACPI specification compliant.
+                        rsdt -- prefer RSDT over (default) XSDT
 
                         See also Documentation/power/pm.txt, pci=noacpi
 
diff --git a/arch/ia64/kernel/acpi.c b/arch/ia64/kernel/acpi.c
index bd7acc71e8a9..c19b686db9b8 100644
--- a/arch/ia64/kernel/acpi.c
+++ b/arch/ia64/kernel/acpi.c
@@ -65,6 +65,7 @@ EXPORT_SYMBOL(pm_idle);
 void (*pm_power_off) (void);
 EXPORT_SYMBOL(pm_power_off);
 
+u32 acpi_rsdt_forced;
 unsigned int acpi_cpei_override;
 unsigned int acpi_cpei_phys_cpuid;
 
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 4c51a2f8fd31..db1a90a76b3e 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -47,7 +47,7 @@
 #endif
 
 static int __initdata acpi_force = 0;
-
+u32 acpi_rsdt_forced;
 #ifdef  CONFIG_ACPI
 int acpi_disabled = 0;
 #else
@@ -1783,6 +1783,10 @@ static int __init parse_acpi(char *arg)
                         disable_acpi();
                 acpi_ht = 1;
         }
+        /* acpi=rsdt use RSDT instead of XSDT */
+        else if (strcmp(arg, "rsdt") == 0) {
+                acpi_rsdt_forced = 1;
+        }
         /* "acpi=noirq" disables ACPI interrupt routing */
         else if (strcmp(arg, "noirq") == 0) {
                 acpi_noirq_set();
diff --git a/drivers/acpi/tables/tbutils.c b/drivers/acpi/tables/tbutils.c
index 0cc92ef5236f..da9f240186e8 100644
--- a/drivers/acpi/tables/tbutils.c
+++ b/drivers/acpi/tables/tbutils.c
@@ -420,7 +420,8 @@ acpi_tb_parse_root_table(acpi_physical_address rsdp_address, u8 flags)
 
         /* Differentiate between RSDT and XSDT root tables */
 
-        if (rsdp->revision > 1 && rsdp->xsdt_physical_address) {
+        if (rsdp->revision > 1 && rsdp->xsdt_physical_address
+                        && !acpi_rsdt_forced) {
                 /*
                  * Root table is an XSDT (64-bit physical addresses). We must use the
                  * XSDT if the revision is > 1 and the XSDT pointer is present, as per
diff --git a/include/acpi/acpixf.h b/include/acpi/acpixf.h
index 33bc0e3b1954..05d2614e0078 100644
--- a/include/acpi/acpixf.h
+++ b/include/acpi/acpixf.h
@@ -48,6 +48,7 @@
 #include "actypes.h"
 #include "actbl.h"
 
+extern u32 acpi_rsdt_forced;
 /*
  * Global interfaces
  */