[ACPI] handle system with NULL DSDT and valid XDSDT

        from ia64 via Alex Williamson

drivers/acpi/tables.c

@@ -276,10 +276,17 @@ acpi_get_table_header_early (
 
 	/* Map the DSDT header via the pointer in the FADT */
 	if (id == ACPI_DSDT) {
-		struct acpi_table_fadt *fadt = (struct acpi_table_fadt *) *header;
+		struct fadt_descriptor_rev2 *fadt = (struct fadt_descriptor_rev2 *) *header;
+
+		if (fadt->revision == 3 && fadt->Xdsdt) {
+			*header = (void *) __acpi_map_table(fadt->Xdsdt,
+					sizeof(struct acpi_table_header));
+		} else if (fadt->V1_dsdt) {
+			*header = (void *) __acpi_map_table(fadt->V1_dsdt,
+					sizeof(struct acpi_table_header));
+		} else
+			*header = 0;
 
-		*header = (void *) __acpi_map_table(fadt->dsdt_addr,
-				sizeof(struct acpi_table_header));
 		if (!*header) {
 			printk(KERN_WARNING PREFIX "Unable to map DSDT\n");
 			return -ENODEV;