[PATCH] fixup for C1 Halt Disconnect problem on nForce2 chipsets

Based on information provided by "Allen Martin" <AMartin@nvidia.com>:

A hang is caused when the CPU generates a very fast CONNECT/HALT cycle
sequence.  Workaround is to set the SYSTEM_IDLE_TIMEOUT to 80 ns.
This allows the state-machine and timer to return to a proper state within
80 ns of the CONNECT and probe appearing together.  Since the CPU will not
issue another HALT within 80 ns of the initial HALT, the failure condition
is avoided.

arch/i386/pci/fixup.c

@@ -187,6 +187,42 @@ static void __devinit pci_fixup_transparent_bridge(struct pci_dev *dev)
 		dev->transparent = 1;
 }
 
+/*
+ * Fixup for C1 Halt Disconnect problem on nForce2 systems.
+ *
+ * From information provided by "Allen Martin" <AMartin@nvidia.com>:
+ *
+ * A hang is caused when the CPU generates a very fast CONNECT/HALT cycle
+ * sequence.  Workaround is to set the SYSTEM_IDLE_TIMEOUT to 80 ns.
+ * This allows the state-machine and timer to return to a proper state within
+ * 80 ns of the CONNECT and probe appearing together.  Since the CPU will not
+ * issue another HALT within 80 ns of the initial HALT, the failure condition
+ * is avoided.
+ */
+static void __init pci_fixup_nforce2(struct pci_dev *dev)
+{
+	u32 val, fixed_val;
+	u8 rev;
+
+	pci_read_config_byte(dev, PCI_REVISION_ID, &rev);
+
+	/*
+	 * Chip  Old value   New value
+	 * C17   0x1F0FFF01  0x1F01FF01
+	 * C18D  0x9F0FFF01  0x9F01FF01
+	 *
+	 * Northbridge chip version may be determined by
+	 * reading the PCI revision ID (0xC1 or greater is C18D).
+	 */
+	fixed_val = rev < 0xC1 ? 0x1F01FF01 : 0x9F01FF01;
+
+	pci_read_config_dword(dev, 0x6c, &val);
+	if (val != fixed_val) {
+		printk(KERN_WARNING "PCI: nForce2 C1 Halt Disconnect fixup\n");
+		pci_write_config_dword(dev, 0x6c, fixed_val);
+	}
+}
+
 struct pci_fixup pcibios_fixups[] = {
 	{
 		.pass		= PCI_FIXUP_HEADER,
@@ -290,5 +326,11 @@ struct pci_fixup pcibios_fixups[] = {
 		.device		= PCI_ANY_ID,
 		.hook		= pci_fixup_transparent_bridge
 	},
+	{
+		.pass		= PCI_FIXUP_HEADER,
+		.vendor		= PCI_VENDOR_ID_NVIDIA,
+		.device		= PCI_DEVICE_ID_NVIDIA_NFORCE2,
+		.hook		= pci_fixup_nforce2
+	},
 	{ .pass = 0 }
 };