--- linux-2.6.9/arch/i386/pci/irq.c~
+++ linux-2.6.9/arch/i386/pci/irq.c
@@ -250,6 +250,44 @@
 }
 
 /*
+ * OPTI Viper-M/N+: Bit field with 3 bits per entry.
+ * Due to the lack of a specification the information about this chipset
+ * was taken from the NetBSD source code.
+ */
+static int pirq_viper_get(struct pci_dev *router, struct pci_dev *dev, int pirq)
+{
+	static const int viper_irq_decode[] = { 0, 5, 9, 10, 11, 12, 14, 15 };
+	u32 irq;
+
+	pci_read_config_dword(router, 0x40, &irq);
+	irq >>= (pirq-1)*3;
+	irq &= 7;
+
+	return viper_irq_decode[irq];
+}
+
+static int pirq_viper_set(struct pci_dev *router, struct pci_dev *dev, int pirq, int irq)
+{
+	static const int viper_irq_map[] = { -1, -1, -1, -1, -1, 1, -1, -1, -1, 2, 3, 4, 5, -1, 6, 7 };
+	int newval = viper_irq_map[irq];
+	u32 val;
+	u32 mask = 7 << (3*(pirq-1));
+#if 0
+	mask |= 0x10000UL << (pirq-1);	/* edge triggered */
+#endif
+
+	if ( newval == -1 )
+		return 0;
+	
+	pci_read_config_dword(router, 0x40, &val);
+	val &= ~mask;
+	val |= newval << (3*(pirq-1));
+	pci_write_config_dword(router, 0x40, val);
+
+	return 1;
+}
+
+/*
  * Cyrix: nibble offset 0x5C
  * 0x5C bits 7:4 is INTB bits 3:0 is INTA 
  * 0x5D bits 7:4 is INTD bits 3:0 is INTC
@@ -567,9 +605,16 @@
 			r->name = "OPTI";
 			r->get = pirq_opti_get;
 			r->set = pirq_opti_set;
-			return 1;
+			break;
+		case PCI_DEVICE_ID_OPTI_82C558:
+			r->name = "OPTI VIPER";
+			r->get = pirq_viper_get;
+			r->set = pirq_viper_set;
+			break;
+		default:
+			return 0;
 	}
-	return 0;
+	return 1;
 }
 
 static __init int ite_router_probe(struct irq_router *r, struct pci_dev *router, u16 device)