Workaround for AMD762MPX "mouse" bug

diff -burp linux/arch/i386/kernel/setup.c linux-tmp/arch/i386/kernel/setup.c
@@ -59,6 +59,8 @@ unsigned long mmu_cr4_features;
 
 int acpi_disabled __initdata = 0;
 
+static int vgaguard __initdata = 0;
+
 int MCA_bus;
 /* for MCA, but anyone else can use it if they want */
 unsigned int machine_id;

@@ -557,6 +559,9 @@ static void __init parse_cmdline_early (
 		if (c == ' ' && !memcmp(from, "acpi=off", 8))
 			acpi_disabled = 1;
 
+		if (c == ' ' && !memcmp(from, "vgaguard", 8))
+			vgaguard = 1;
+
 		/*
 		 * highmem=size forces highmem to be exactly 'size' bytes.
 		 * This works even on boxes that have no highmem otherwise.

@@ -748,6 +753,10 @@ static unsigned long __init setup_memory
 	 */
 	reserve_bootmem(0, PAGE_SIZE);
 
+	/* work around AMD-762 errata 56 - prefetch into VGA */
+	if (vgaguard)
+	     reserve_bootmem(640*1024 - PAGE_SIZE, PAGE_SIZE);
+
 #ifdef CONFIG_SMP
 	/*
 	 * But first pinch a few for the stack/trampoline stuff

diff -burp linux/drivers/pci/quirks.c linux-tmp/drivers/pci/quirks.c
@@ -349,6 +349,24 @@ static void __devinit quirk_amd_ioapic(s
 	}
 }
 
+/* Some AMD 762 chips hang when a PCI busmaster prefetches into the VGA text buffer
+   at 640K. Workaround is to put a suitable guard page before it
+   Connecting an PS/2 mouse has the same effect, in this case the BIOS reserves
+   an data area there. We cannot detect this in early boot, so tell the user to pass 
+   an option to work around. In theory it would be possible to check the E820
+   MAP for a suitable guard page and not print it then. */
+static void __devinit quirk_amd_ioapic2(struct pci_dev *dev)
+{
+	u8 rev;
+
+	pci_read_config_byte(dev, PCI_REVISION_ID, &rev);
+	if(rev >= 0x10) /* B0+ */
+	{
+		printk(KERN_WARNING "I/O APIC: AMD762 Errata #56 may be present.\n"
+		       KERN_WARNING "In case of instability boot with \"vgaguard\" or connect a PS/2 mouse.\n");
+	}
+}
+
 static void __init quirk_ioapic_rmw(struct pci_dev *dev)
 {
 	if (dev->devfn == 0 && dev->bus->number == 0)

@@ -604,6 +622,7 @@ static struct pci_fixup pci_fixups[] __d
 
 	{ PCI_FIXUP_FINAL,	PCI_VENDOR_ID_CYRIX,	PCI_DEVICE_ID_CYRIX_PCI_MASTER, quirk_mediagx_master },
 	
+	{ PCI_FIXUP_FINAL, 	PCI_VENDOR_ID_AMD,	PCI_DEVICE_ID_AMD_FE_GATE_700C,	quirk_amd_ioapic2 },
 
 	{ 0 }
 };