force HPET support on buggy NVidia-based machines

diff -r bf828db8d017 xen/arch/x86/time.c
@@ -320,6 +320,130 @@ static u32 read_hpet_count(void)
     return hpet_read32(HPET_COUNTER);
 }
 
+#define PDprintk(x...)
+
+static inline u32 read_pci_config(u8 bus, u8 slot, u8 func, u8 offset)
+{
+    u32 v;
+    outl(0x80000000 | (bus<<16) | (slot<<11) | (func<<8) | offset, 0xcf8);
+    v = inl(0xcfc);
+    if (v != 0xffffffff)
+        PDprintk("%x reading 4 from %x: %x\n", slot, offset, v);
+    return v;
+}
+
+static inline u8 read_pci_config_byte(u8 bus, u8 slot, u8 func, u8 offset)
+{
+    u8 v;
+    outl(0x80000000 | (bus<<16) | (slot<<11) | (func<<8) | offset, 0xcf8);
+    v = inb(0xcfc + (offset&3));
+    PDprintk("%x reading 1 from %x: %x\n", slot, offset, v);
+    return v;
+}
+
+
+static void detect_nforce_hpet(int num, int slot, int func)
+{
+	u32 addr;
+
+	addr = read_pci_config(num, slot, func, 0x44);
+	if (!addr) {
+		return;
+	}
+
+	hpet_address = addr;
+	printk(KERN_INFO "NVidia quirk. Enabled hidden HPET that BIOS had "
+	       "configured at base: %#x\n", addr);
+}
+
+struct pci_entry {
+	u16 class;
+	u16 vendor;
+	u16 device;
+	void (*f)(int num, int slot, int func);
+};
+
+#define PCI_HEADER_TYPE                 0x0e
+#define PCI_VENDOR_ID			0x00
+#define PCI_CLASS_REVISION   		0x08
+#define PCI_CLASS_BRIDGE_ISA            0x0601
+#define PCI_VENDOR_ID_NVIDIA            0x10de
+
+
+static struct pci_entry nforce_hpet_chips[] __initdata = {
+	{ PCI_CLASS_BRIDGE_ISA, PCI_VENDOR_ID_NVIDIA, 0x0050, detect_nforce_hpet },
+	{ PCI_CLASS_BRIDGE_ISA, PCI_VENDOR_ID_NVIDIA, 0x0051, detect_nforce_hpet },
+	{ PCI_CLASS_BRIDGE_ISA, PCI_VENDOR_ID_NVIDIA, 0x0360, detect_nforce_hpet },
+	{ PCI_CLASS_BRIDGE_ISA, PCI_VENDOR_ID_NVIDIA, 0x0361, detect_nforce_hpet },
+	{ PCI_CLASS_BRIDGE_ISA, PCI_VENDOR_ID_NVIDIA, 0x0362, detect_nforce_hpet },
+	{ PCI_CLASS_BRIDGE_ISA, PCI_VENDOR_ID_NVIDIA, 0x0363, detect_nforce_hpet },
+	{ PCI_CLASS_BRIDGE_ISA, PCI_VENDOR_ID_NVIDIA, 0x0364, detect_nforce_hpet },
+	{ PCI_CLASS_BRIDGE_ISA, PCI_VENDOR_ID_NVIDIA, 0x0365, detect_nforce_hpet },
+	{ PCI_CLASS_BRIDGE_ISA, PCI_VENDOR_ID_NVIDIA, 0x0366, detect_nforce_hpet },
+	{ PCI_CLASS_BRIDGE_ISA, PCI_VENDOR_ID_NVIDIA, 0x0367, detect_nforce_hpet },
+	{}
+};
+
+
+void early_pci_scan(struct pci_entry matching[])
+{
+	int num, slot, func;
+
+	/* Poor man's PCI discovery */
+	for (num = 0; num < 32; num++) {
+		for (slot = 0; slot < 32; slot++) {
+			for (func = 0; func < 8; func++) {
+				u32 class;
+				u32 vendor;
+				u8 type;
+				int i;
+				class = read_pci_config(num,slot,func,
+							PCI_CLASS_REVISION);
+				if (class == 0xffffffff)
+					break;
+
+				class >>= 16;
+
+				vendor = read_pci_config(num, slot, func,
+							 PCI_VENDOR_ID);
+
+				for (i = 0; matching[i].f; i++) {
+					if (class != matching[i].class)
+						continue;
+
+					if ((vendor & 0xffff) != matching[i].vendor)
+						continue;
+
+					if (matching[i].device != 0xffff &&
+					    (vendor >> 16) != matching[i].device)
+						continue;
+
+					matching[i].f(num, slot, func);
+					return;
+				}
+
+				/* No multi-function device? */
+				type = read_pci_config_byte(num,slot,func,
+							    PCI_HEADER_TYPE);
+				if (!(type & 0x80))
+					break;
+			}
+		}
+	}
+}
+
+static int enable_nvidia_hpet(void)
+{
+	if (hpet_address)
+		return 0;
+
+	early_pci_scan(nforce_hpet_chips);
+
+	return hpet_address != 0;
+}
+
+
+
 static int init_hpet(struct platform_timesource *pts)
 {
     u64 hpet_rate;

@@ -540,6 +664,11 @@ static void init_platform_timer(void)
             rc = (init_pit(pts), 1);
         else if ( !strcmp(opt_clocksource, "hpet") )
             rc = init_hpet(pts);
+        else if ( !strcmp(opt_clocksource, "hpet_nv") ) 
+        {
+            enable_nvidia_hpet();
+	    rc = init_hpet(pts);
+        }
         else if ( !strcmp(opt_clocksource, "cyclone") )
             rc = init_cyclone(pts);
         else if ( !strcmp(opt_clocksource, "acpi") )