[PATCH] powerpc: Fix PowerMac IRQ handling bug

The port to genirq & the new powerpc interrupt model in 2.6.18 introduced a
bug in the legacy PowerMac PIC code (used on older machines) because of a
typo potentially causing hangs due to interrupt storms. This fixes it,
along with a performance issue causing us to do spurrious retriggers after
masking an interrupt.

Signed-off-by: Benjamin Herrenschmidt <[e-mail]>
Cc: "Antonino A. Daplas" <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/powerpc/platforms/powermac/pic.c

···
 static void pmac_mask_and_ack_irq(unsigned int virq)
 {
 	unsigned int src = irq_map[virq].hwirq;
-        unsigned long bit = 1UL << (virq & 0x1f);
-        int i = virq >> 5;
+        unsigned long bit = 1UL << (src & 0x1f);
+        int i = src >> 5;
         unsigned long flags;
 
 	spin_lock_irqsave(&pmac_pic_lock, flags);
···
 
   	spin_lock_irqsave(&pmac_pic_lock, flags);
         __clear_bit(src, ppc_cached_irq_mask);
-        __pmac_set_irq_mask(src, 0);
+        __pmac_set_irq_mask(src, 1);
   	spin_unlock_irqrestore(&pmac_pic_lock, flags);
 }