This patch introduces an option to force PS/2 USB emulation off.  Most
of the patch is by Vojtech Pavlik, I only updated it to 2.6.9ish
kernel and made it conditional on the nops2usbemul option.

--- a/drivers/pci/quirks.c	2004-10-17 04:24:28.000000000 -0300
+++ b/drivers/pci/quirks.c	2004-10-17 15:19:35.000000000 -0300
@@ -545,6 +545,76 @@
 }
 DECLARE_PCI_FIXUP_FINAL(PCI_ANY_ID,		PCI_ANY_ID,			quirk_cardbus_legacy );
 
+#if defined(__i386__) || defined(__x86_64__)
+#define UHCI_USBLEGSUP 0xc0 /* legacy support */
+#define UHCI_USBCMD 0 /* command register */
+#define UHCI_USBINTR 4 /* interrupt register */
+#define UHCI_USBLEGSUP_DEFAULT 0x2000 /* only PIRQ enable set */
+#define UHCI_USBCMD_GRESET 0x0004 /* Global reset */
+
+#define OHCI_CONTROL 0x04
+#define OHCI_CMDSTATUS 0x08
+#define OHCI_INTRENABLE 0x10
+#define OHCI_OCR (1 << 3) /* ownership change request */
+#define OHCI_CTRL_IR (1 << 8) /* interrupt routing */
+#define OHCI_INTR_OC (1 << 30) /* ownership change */
+
+/* If the BIOS doesn't have an option to disable legacy USB emulation,
+   and such emulation actually gets in the way of proper probing of
+   PS/2 devices, the nops2usbemul option should help.  */
+static void __init quirk_usb_disable_smm_bios(struct pci_dev *pdev)
+{
+  extern char saved_command_line[];
+
+  if (!strstr(saved_command_line, "nops2usbemul"))
+    return;
+
+  if (pdev->class == ((PCI_CLASS_SERIAL_USB << 8) | 0x00)) { /* UHCI */
+    int i;
+    unsigned long base = 0;;
+
+    for (i = 0; i < PCI_ROM_RESOURCE; i++)
+      if ((pci_resource_flags(pdev, i) & IORESOURCE_IO)) {
+	base = pci_resource_start(pdev, i);
+	break;
+      }
+
+    if (!base)
+      return;
+
+    outw(0, base + UHCI_USBINTR);
+    outw(UHCI_USBCMD_GRESET, base + UHCI_USBCMD);
+    set_current_state(TASK_UNINTERRUPTIBLE);
+    schedule_timeout((HZ*50+999) / 1000);
+    outw(0, base + UHCI_USBCMD);
+    set_current_state(TASK_UNINTERRUPTIBLE);
+    schedule_timeout((HZ*10+999) / 1000);
+
+    pci_write_config_word(pdev, UHCI_USBLEGSUP, UHCI_USBLEGSUP_DEFAULT);
+  }
+
+  if (pdev->class == ((PCI_CLASS_SERIAL_USB << 8) | 0x10)) { /* OHCI */
+    char *base = ioremap_nocache(pci_resource_start(pdev, 0),
+				 pci_resource_len(pdev, 0));
+    if (base == NULL) return;
+
+    if (readl(base + OHCI_CONTROL) & OHCI_CTRL_IR) {
+      int temp = 500; /* arbitrary: five seconds */
+      writel(OHCI_INTR_OC, base + OHCI_INTRENABLE);
+      writel(OHCI_OCR, base + OHCI_CMDSTATUS);
+      while (temp && readl(base + OHCI_CONTROL) & OHCI_CTRL_IR) {
+	temp--;
+	set_current_state(TASK_UNINTERRUPTIBLE);
+	schedule_timeout( HZ / 100);
+      }
+    }
+    iounmap(base);
+  }
+}
+
+DECLARE_PCI_FIXUP_FINAL(PCI_ANY_ID, PCI_ANY_ID, quirk_usb_disable_smm_bios);
+#endif
+
 /*
  * Following the PCI ordering rules is optional on the AMD762. I'm not
  * sure what the designers were smoking but let's not inhale...

--- a/Documentation/kernel-parameters.txt	2004-10-17 04:23:11.000000000 -0300
+++ b/Documentation/kernel-parameters.txt	2004-10-17 15:19:15.000000000 -0300
@@ -818,6 +818,8 @@
 
 	nousb		[USB] Disable the USB subsystem
 
+	nops2usbemul	[PCI,IA-32,X86_64] Disable PS/2 USB emulation
+
 	nowb		[ARM]
  
 	opl3=		[HW,OSS]