diff -urN 2.4.5ac2/arch/alpha/kernel/sys_rawhide.c 2.4.5ac3/arch/alpha/kernel/sys_rawhide.c
--- 2.4.5ac2/arch/alpha/kernel/sys_rawhide.c	Sun Apr  1 01:17:07 2001
+++ 2.4.5ac3/arch/alpha/kernel/sys_rawhide.c	Mon May 28 20:07:11 2001
@@ -59,10 +59,11 @@
 	irq -= 16;
 	hose = irq / 24;
 	irq -= hose * 24;
+	mask = 1 << irq;
 
 	spin_lock(&rawhide_irq_lock);
-	mask = cached_irq_masks[hose] |= 1 << irq;
-	mask |= hose_irq_masks[hose];
+	mask |= cached_irq_masks[hose];
+	cached_irq_masks[hose] = mask;
 	rawhide_update_irq_hw(hose, mask);
 	spin_unlock(&rawhide_irq_lock);
 }
@@ -75,14 +76,37 @@
 	irq -= 16;
 	hose = irq / 24;
 	irq -= hose * 24;
+	mask = ~(1 << irq) | hose_irq_masks[hose];
 
 	spin_lock(&rawhide_irq_lock);
-	mask = cached_irq_masks[hose] &= ~(1 << irq);
-	mask |= hose_irq_masks[hose];
+	mask &= cached_irq_masks[hose];
+	cached_irq_masks[hose] = mask;
 	rawhide_update_irq_hw(hose, mask);
 	spin_unlock(&rawhide_irq_lock);
 }
 
+static void
+rawhide_mask_and_ack_irq(unsigned int irq)
+{
+	unsigned int mask, mask1, hose;
+
+	irq -= 16;
+	hose = irq / 24;
+	irq -= hose * 24;
+	mask1 = 1 << irq;
+	mask = ~mask1 | hose_irq_masks[hose];
+
+	spin_lock(&rawhide_irq_lock);
+
+	mask &= cached_irq_masks[hose];
+	cached_irq_masks[hose] = mask;
+	rawhide_update_irq_hw(hose, mask);
+
+	/* Clear the interrupt.  */
+	*(vuip)MCPCIA_INT_REQ(MCPCIA_HOSE2MID(hose)) = mask1;
+
+	spin_unlock(&rawhide_irq_lock);
+}
 
 static unsigned int
 rawhide_startup_irq(unsigned int irq)
@@ -104,7 +128,7 @@
 	shutdown:	rawhide_disable_irq,
 	enable:		rawhide_enable_irq,
 	disable:	rawhide_disable_irq,
-	ack:		rawhide_disable_irq,
+	ack:		rawhide_mask_and_ack_irq,
 	end:		rawhide_end_irq,
 };
 
@@ -145,8 +169,12 @@
 	mcpcia_init_hoses();
 
 	for (hose = hose_head; hose; hose = hose->next) {
-		int h = hose->index;
-		rawhide_update_irq_hw(h, hose_irq_masks[h]);
+		unsigned int h = hose->index;
+		unsigned int mask = hose_irq_masks[h];
+
+		cached_irq_masks[h] = mask;
+		*(vuip)MCPCIA_INT_MASK0(MCPCIA_HOSE2MID(h)) = mask;
+		*(vuip)MCPCIA_INT_MASK1(MCPCIA_HOSE2MID(h)) = 0;
 	}
 
 	for (i = 16; i < 128; ++i) {