ACPI : Use RSDT instead of XSDT by adding boot option of "acpi=rsdt"

On some boxes there exist both RSDT and XSDT table. But unfortunately
sometimes there exists the following error when XSDT table is used:
   a. 32/64X address mismatch
   b. The 32/64X FACS address mismatch

   In such case the boot option of "acpi=rsdt" is provided so that
RSDT is tried instead of XSDT table when the system can't work well.

http://bugzilla.kernel.org/show_bug.cgi?id=8246

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
cc:Thomas Renninger <trenn@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>

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
 

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;
 

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();

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

include/acpi/acpixf.h

@@ -48,6 +48,7 @@
 #include "actypes.h"
 #include "actbl.h"
 
+extern u32 acpi_rsdt_forced;
 /*
  * Global interfaces
  */