[PATCH] Allow more APIC irq sources

The "irq_vector[]" array is indexed by the sum of all RTEs in all I/O
APICs, and is not necessarily limited by the x86 CPU irq vector inputs.

In fact, the irq vector index would overflow on big machines with lots
of IO APIC's, causing the boot to fail.

So grow the array for the big SMP boxes, keeping the default the same as
before (and shrink the vector entry size down to a 8-bit value, since
that's the size of the actual CPU vector entry).

arch/i386/kernel/io_apic.c

@@ -1138,12 +1138,13 @@ static inline int IO_APIC_irq_trigger(int irq)
 	return 0;
 }
 
-int irq_vector[NR_IRQS] = { FIRST_DEVICE_VECTOR , 0 };
+/* irq_vectors is indexed by the sum of all RTEs in all I/O APICs. */
+u8 irq_vector[NR_IRQ_VECTORS] = { FIRST_DEVICE_VECTOR , 0 };
 
 static int __init assign_irq_vector(int irq)
 {
 	static int current_vector = FIRST_DEVICE_VECTOR, offset = 0;
-	BUG_ON(irq >= NR_IRQS);
+	BUG_ON(irq >= NR_IRQ_VECTORS);
 	if (IO_APIC_VECTOR(irq) > 0)
 		return IO_APIC_VECTOR(irq);
 next:

include/asm-i386/hw_irq.h

@@ -25,8 +25,8 @@
  * Interrupt entry/exit code at both C and assembly level
  */
 
-extern int irq_vector[NR_IRQS];
-#define IO_APIC_VECTOR(irq)	irq_vector[irq]
+extern u8 irq_vector[NR_IRQ_VECTORS];
+#define IO_APIC_VECTOR(irq)	((int)irq_vector[irq])
 
 extern void (*interrupt[NR_IRQS])(void);
 

include/asm-i386/mach-default/irq_vectors.h

@@ -78,8 +78,14 @@
  */
 #ifdef CONFIG_X86_IO_APIC
 #define NR_IRQS 224
+# if (224 >= 32 * NR_CPUS)
+# define NR_IRQ_VECTORS NR_IRQS
+# else
+# define NR_IRQ_VECTORS (32 * NR_CPUS)
+# endif
 #else
 #define NR_IRQS 16
+#define NR_IRQ_VECTORS NR_IRQS
 #endif
 
 #define FPU_IRQ			13