smp, generic: introduce arch_disable_smp_support() instead of disable_ioapic_setup()

Impact: cleanup

disable_ioapic_setup() in init/main.c is ugly as the function is
x86-specific. The #ifdef inline prototype there is ugly too.

Replace it with a generic arch_disable_smp_support() function - which
has a weak alias for non-x86 architectures and for non-ioapic x86 builds.
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/io_apic.h

@@ -143,15 +143,6 @@ extern int noioapicreroute;
 /* 1 if the timer IRQ uses the '8259A Virtual Wire' mode */
 extern int timer_through_8259;
 
-static inline void disable_ioapic_setup(void)
-{
-#ifdef CONFIG_PCI
-	noioapicquirk = 1;
-	noioapicreroute = -1;
-#endif
-	skip_ioapic_setup = 1;
-}
-
 /*
  * If we use the IO-APIC for IRQ routing, disable automatic
  * assignment of PCI IRQ's.

arch/x86/kernel/apic.c

@@ -1138,9 +1138,7 @@ void __cpuinit setup_local_APIC(void)
 	int i, j;
 
 	if (disable_apic) {
-#ifdef CONFIG_X86_IO_APIC
-		disable_ioapic_setup();
-#endif
+		arch_disable_smp_support();
 		return;
 	}
 

arch/x86/kernel/io_apic.c

@@ -98,10 +98,19 @@ DECLARE_BITMAP(mp_bus_not_pci, MAX_MP_BUSSES);
 
 int skip_ioapic_setup;
 
+void arch_disable_smp_support(void)
+{
+#ifdef CONFIG_PCI
+	noioapicquirk = 1;
+	noioapicreroute = -1;
+#endif
+	skip_ioapic_setup = 1;
+}
+
 static int __init parse_noapic(char *str)
 {
 	/* disable IO-APIC */
-	disable_ioapic_setup();
+	arch_disable_smp_support();
 	return 0;
 }
 early_param("noapic", parse_noapic);

arch/x86/kernel/smpboot.c

@@ -1071,7 +1071,7 @@ static int __init smp_sanity_check(unsigned max_cpus)
 		printk(KERN_ERR "... forcing use of dummy APIC emulation."
 				"(tell your hw vendor)\n");
 		smpboot_clear_io_apic();
-		disable_ioapic_setup();
+		arch_disable_smp_support();
 		return -1;
 	}
 

include/linux/smp.h

@@ -66,6 +66,12 @@ extern int __cpu_up(unsigned int cpunum);
  */
 extern void smp_cpus_done(unsigned int max_cpus);
 
+/*
+ * Callback to arch code if there's nosmp or maxcpus=0 on the
+ * boot command line:
+ */
+extern void arch_disable_smp_support(void);
+
 /*
  * Call a function on all other processors
  */

init/main.c

@@ -136,14 +136,14 @@ unsigned int __initdata setup_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
+
+void __weak arch_disable_smp_support(void) { }
 
 static int __init nosmp(char *str)
 {
 	setup_max_cpus = 0;
-	disable_ioapic_setup();
+	arch_disable_smp_support();
+
 	return 0;
 }
 
@@ -153,14 +153,14 @@ static int __init maxcpus(char *str)
 {
 	get_option(&str, &setup_max_cpus);
 	if (setup_max_cpus == 0)
-		disable_ioapic_setup();
+		arch_disable_smp_support();
 
 	return 0;
 }
 
 early_param("maxcpus", maxcpus);
 #else
-#define setup_max_cpus NR_CPUS
+const unsigned int setup_max_cpus = NR_CPUS;
 #endif
 
 /*