ACPI: boot correctly with "nosmp" or "maxcpus=0"

In MPS mode, "nosmp" and "maxcpus=0" boot a UP kernel with IOAPIC disabled.
However, in ACPI mode, these parameters didn't completely disable
the IO APIC initialization code and boot failed.

init/main.c:
	Disable the IO_APIC if "nosmp" or "maxcpus=0"
	undefine disable_ioapic_setup() when it doesn't apply.

i386:
	delete ioapic_setup(), it was a duplicate of parse_noapic()
	delete undefinition of disable_ioapic_setup()

x86_64:
	rename disable_ioapic_setup() to parse_noapic() to match i386
	define disable_ioapic_setup() in header to match i386

http://bugzilla.kernel.org/show_bug.cgi?id=1641

Acked-by: Andi Kleen <ak@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>

Documentation/kernel-parameters.txt

@@ -952,14 +952,10 @@ and is between 256 and 4096 characters. It is defined in the file
 			Format: <1-256>
 
 	maxcpus=	[SMP] Maximum number of processors that	an SMP kernel
-			should make use of.
-			Using "nosmp" or "maxcpus=0" will disable SMP
-			entirely (the MPS table probe still happens, though).
-			A command-line option of "maxcpus=<NUM>", where <NUM>
-			is an integer greater than 0, limits the maximum number
-			of CPUs activated in SMP mode to <NUM>.
-			Using "maxcpus=1" on an SMP kernel is the trivial
-			case of an SMP kernel with only one CPU.
+			should make use of.  maxcpus=n : n >= 0 limits the
+			kernel to using 'n' processors.  n=0 is a special case,
+			it is equivalent to "nosmp", which also disables
+			the IO APIC.
 
 	max_addr=[KMG]	[KNL,BOOT,ia64] All physical memory greater than or
 			equal to this physical address is ignored.
@@ -1184,7 +1180,8 @@ and is between 256 and 4096 characters. It is defined in the file
 
 	nosep		[BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
 
-	nosmp		[SMP] Tells an SMP kernel to act as a UP kernel.
+	nosmp		[SMP] Tells an SMP kernel to act as a UP kernel,
+			and disable the IO APIC.  legacy for "maxcpus=0".
 
 	nosoftlockup	[KNL] Disable the soft-lockup detector.
 

arch/i386/kernel/io_apic.c

@@ -754,14 +754,6 @@ static int pirq_entries [MAX_PIRQS];
 static int pirqs_enabled;
 int skip_ioapic_setup;
 
-static int __init ioapic_setup(char *str)
-{
-	skip_ioapic_setup = 1;
-	return 1;
-}
-
-__setup("noapic", ioapic_setup);
-
 static int __init ioapic_pirq_setup(char *str)
 {
 	int i, max;

arch/x86_64/kernel/io_apic.c

@@ -397,14 +397,12 @@ static void clear_IO_APIC (void)
 int skip_ioapic_setup;
 int ioapic_force;
 
-/* dummy parsing: see setup.c */
-
-static int __init disable_ioapic_setup(char *str)
+static int __init parse_noapic(char *str)
 {
-	skip_ioapic_setup = 1;
+	disable_ioapic_setup();
 	return 0;
 }
-early_param("noapic", disable_ioapic_setup);
+early_param("noapic", parse_noapic);
 
 /* Actually the next is obsolete, but keep it for paranoid reasons -AK */
 static int __init disable_timer_pin_setup(char *arg)

include/asm-i386/io_apic.h

@@ -150,7 +150,6 @@ extern int (*ioapic_renumber_irq)(int ioapic, int irq);
 
 #else  /* !CONFIG_X86_IO_APIC */
 #define io_apic_assign_pci_irqs 0
-static inline void disable_ioapic_setup(void) { }
 #endif
 
 #endif

include/asm-x86_64/io_apic.h

@@ -109,6 +109,12 @@ extern int mpc_default_type;
 /* 1 if "noapic" boot option passed */
 extern int skip_ioapic_setup;
 
+static inline void disable_ioapic_setup(void)
+{
+	skip_ioapic_setup = 1;
+}
+
+
 /*
  * If we use the IO-APIC for IRQ routing, disable automatic
  * assignment of PCI IRQ's.

init/main.c

@@ -146,9 +146,14 @@ static unsigned int __initdata max_cpus = NR_CPUS;
  * greater than 0, limits the maximum number of CPUs activated in
  * SMP mode to <NUM>.
  */
+#ifndef CONFIG_X86_IO_APIC
+static inline void disable_ioapic_setup(void) {};
+#endif
+
 static int __init nosmp(char *str)
 {
 	max_cpus = 0;
+	disable_ioapic_setup();
 	return 0;
 }
 
@@ -157,10 +162,13 @@ early_param("nosmp", nosmp);
 static int __init maxcpus(char *str)
 {
 	get_option(&str, &max_cpus);
-	return 1;
+	if (max_cpus == 0)
+		disable_ioapic_setup();
+
+	return 0;
 }
 
-__setup("maxcpus=", maxcpus);
+early_param("maxcpus=", maxcpus);
 #else
 #define max_cpus NR_CPUS
 #endif