There are a few problems with ACPI init. One of these is that acpi=off

will disable the ACPI interpreter init, but not stop the OS from using
ACPI tables for finding CPUs and IOAPICs. Another problem is that if we
use the tables, but then the interpreter fails to init, we are in deep
trouble, because it is too late to revert to using MPS, but we cannot get
_PRT info without the interpreter.

This changeset doesn't fix the latter problem, but it does at least make
"acpi=off" actually do what it says, and not use the ACPI interpreter *or*
the tables.

arch/i386/kernel/setup.c

@@ -46,6 +46,8 @@ struct cpuinfo_x86 boot_cpu_data = { 0, 0, 0, 0, -1, 1, 0, 0, -1 };
 
 unsigned long mmu_cr4_features;
 
+int acpi_disabled __initdata = 0;
+
 int MCA_bus;
 /* for MCA, but anyone else can use it if they want */
 unsigned int machine_id;
@@ -522,7 +524,7 @@ static void __init setup_memory_region(void)
 } /* setup_memory_region */
 
 
-static void __init parse_mem_cmdline (char ** cmdline_p)
+static void __init parse_cmdline_early (char ** cmdline_p)
 {
 	char c = ' ', *to = command_line, *from = COMMAND_LINE;
 	int len = 0;
@@ -569,6 +571,11 @@ static void __init parse_mem_cmdline (char ** cmdline_p)
 				}
 			}
 		}
+
+		/* "acpi=off" disables both ACPI table parsing and interpreter init */
+		if (c == ' ' && !memcmp(from, "acpi=off", 8))
+			acpi_disabled = 1;
+
 		/*
 		 * highmem=size forces highmem to be exactly 'size' bytes.
 		 * This works even on boxes that have no highmem otherwise.
@@ -637,7 +644,7 @@ void __init setup_arch(char **cmdline_p)
 	data_resource.start = virt_to_phys(&_etext);
 	data_resource.end = virt_to_phys(&_edata)-1;
 
-	parse_mem_cmdline(cmdline_p);
+	parse_cmdline_early(cmdline_p);
 
 #define PFN_UP(x)	(((x) + PAGE_SIZE-1) >> PAGE_SHIFT)
 #define PFN_DOWN(x)	((x) >> PAGE_SHIFT)
@@ -840,7 +847,8 @@ void __init setup_arch(char **cmdline_p)
 	/*
 	 * Parse the ACPI tables for possible boot-time SMP configuration.
 	 */
-	acpi_boot_init(*cmdline_p);
+	if (!acpi_disabled)
+		acpi_boot_init(*cmdline_p);
 #endif
 #ifdef CONFIG_X86_LOCAL_APIC
 	if (smp_found_config)

drivers/acpi/bus.c

@@ -46,8 +46,10 @@ MODULE_LICENSE("GPL");
 
 #define	PREFIX			"ACPI: "
 
+
+extern int			acpi_disabled;
+
 FADT_DESCRIPTOR			acpi_fadt;
-static u8			acpi_disabled;
 struct acpi_device		*acpi_root;
 struct proc_dir_entry		*acpi_root_dir;