Index: head/sys/x86/pci/qpi.c
===================================================================
--- head/sys/x86/pci/qpi.c
+++ head/sys/x86/pci/qpi.c
@@ -63,13 +63,19 @@
 static void
 qpi_identify(driver_t *driver, device_t parent)
 {
+	int do_qpi;
 
 	/* Check CPUID to ensure this is an i7 CPU of some sort. */
-	if (!(cpu_vendor_id == CPU_VENDOR_INTEL &&
-	    CPUID_TO_FAMILY(cpu_id) == 0x6 &&
-	    (CPUID_TO_MODEL(cpu_id) == 0x1a || CPUID_TO_MODEL(cpu_id) == 0x2c)))
+	if (cpu_vendor_id != CPU_VENDOR_INTEL ||
+	    CPUID_TO_FAMILY(cpu_id) != 0x6)
 		return;
 
+	/* Only discover buses with configuration devices if allowed by user */
+	do_qpi = 0;
+	TUNABLE_INT_FETCH("hw.attach_intel_csr_pci", &do_qpi);
+	if (!do_qpi)
+		return;
+
 	/* PCI config register access is required. */
 	if (pci_cfgregopen() == 0)
 		return;
@@ -97,6 +103,7 @@
 	struct qpi_device *qdev;
 	device_t child;
 	uint32_t devid;
+	int s;
 
 	/*
 	 * If a PCI bus already exists for this bus number, then
@@ -106,18 +113,23 @@
 		return (EEXIST);
 
 	/*
-	 * Attempt to read the device id for device 0, function 0 on
-	 * the bus.  A value of 0xffffffff means that the bus is not
-	 * present.
+	 * Attempt to read the device id for every slot, function 0 on
+	 * the bus.  If all read values are 0xffffffff this means that
+	 * the bus is not present.
 	 */
-	devid = pci_cfgregread(bus, 0, 0, PCIR_DEVVENDOR, 4);
+	for (s = 0; s <= PCI_SLOTMAX; s++) {
+		devid = pci_cfgregread(bus, s, 0, PCIR_DEVVENDOR, 4);
+		if (devid != 0xffffffff)
+			break;
+	}
 	if (devid == 0xffffffff)
 		return (ENOENT);
 
 	if ((devid & 0xffff) != 0x8086) {
-		device_printf(dev,
-		    "Device at pci%d.0.0 has non-Intel vendor 0x%x\n", bus,
-		    devid & 0xffff);
+		if (bootverbose)
+			device_printf(dev,
+			    "Device at pci%d.%d.0 has non-Intel vendor 0x%x\n",
+			    bus, s, devid & 0xffff);
 		return (ENXIO);
 	}
 
@@ -137,12 +149,12 @@
 	int bus;
 
 	/*
-	 * Each processor socket has a dedicated PCI bus counting down from
-	 * 255.  We keep probing buses until one fails.
+	 * Each processor socket has a dedicated PCI bus, sometimes
+	 * not enumerated by ACPI.  Probe all unattached buses from 0
+	 * to 255.
 	 */
-	for (bus = 255;; bus--)
-		if (qpi_probe_pcib(dev, bus) != 0)
-			break;
+	for (bus = PCI_BUSMAX; bus >= 0; bus--)
+		qpi_probe_pcib(dev, bus);
 
 	return (bus_generic_attach(dev));
 }