diff --git a/arch/ia64/pci/pci.c b/arch/ia64/pci/pci.c
index 64aff520b899..aa2533ae7e9e 100644
--- a/arch/ia64/pci/pci.c
+++ b/arch/ia64/pci/pci.c
@@ -335,8 +335,11 @@ pcibios_setup_root_windows(struct pci_bus *bus, struct pci_controller *ctrl)
 }
 
 struct pci_bus * __devinit
-pci_acpi_scan_root(struct acpi_device *device, int domain, int bus)
+pci_acpi_scan_root(struct acpi_pci_root *root)
 {
+	struct acpi_device *device = root->device;
+	int domain = root->segment;
+	int bus = root->secondary.start;
 	struct pci_controller *controller;
 	unsigned int windows = 0;
 	struct pci_bus *pbus;
diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
index 31930fd30ea9..9dcf43d7d0c0 100644
--- a/arch/x86/pci/acpi.c
+++ b/arch/x86/pci/acpi.c
@@ -224,8 +224,11 @@ get_current_resources(struct acpi_device *device, int busnum,
 	return;
 }
 
-struct pci_bus * __devinit pci_acpi_scan_root(struct acpi_device *device, int domain, int busnum)
+struct pci_bus * __devinit pci_acpi_scan_root(struct acpi_pci_root *root)
 {
+	struct acpi_device *device = root->device;
+	int domain = root->segment;
+	int busnum = root->secondary.start;
 	struct pci_bus *bus;
 	struct pci_sysdata *sd;
 	int node;
diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index aefce33f2a09..4eac59393edc 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -120,7 +120,8 @@ acpi_handle acpi_get_pci_rootbridge_handle(unsigned int seg, unsigned int bus)
 	struct acpi_pci_root *root;
 	
 	list_for_each_entry(root, &acpi_pci_roots, node)
-		if ((root->segment == (u16) seg) && (root->bus_nr == (u16) bus))
+		if ((root->segment == (u16) seg) &&
+		    (root->secondary.start == (u16) bus))
 			return root->device->handle;
 	return NULL;		
 }
@@ -154,7 +155,7 @@ EXPORT_SYMBOL_GPL(acpi_is_root_bridge);
 static acpi_status
 get_root_bridge_busnr_callback(struct acpi_resource *resource, void *data)
 {
-	int *busnr = data;
+	struct resource *res = data;
 	struct acpi_resource_address64 address;
 
 	if (resource->type != ACPI_RESOURCE_TYPE_ADDRESS16 &&
@@ -164,28 +165,27 @@ get_root_bridge_busnr_callback(struct acpi_resource *resource, void *data)
 
 	acpi_resource_to_address64(resource, &address);
 	if ((address.address_length > 0) &&
-	    (address.resource_type == ACPI_BUS_NUMBER_RANGE))
-		*busnr = address.minimum;
+	    (address.resource_type == ACPI_BUS_NUMBER_RANGE)) {
+		res->start = address.minimum;
+		res->end = address.minimum + address.address_length - 1;
+	}
 
 	return AE_OK;
 }
 
 static acpi_status try_get_root_bridge_busnr(acpi_handle handle,
-					     unsigned long long *bus)
+					     struct resource *res)
 {
 	acpi_status status;
-	int busnum;
 
-	busnum = -1;
+	res->start = -1;
 	status =
 	    acpi_walk_resources(handle, METHOD_NAME__CRS,
-				get_root_bridge_busnr_callback, &busnum);
+				get_root_bridge_busnr_callback, res);
 	if (ACPI_FAILURE(status))
 		return status;
-	/* Check if we really get a bus number from _CRS */
-	if (busnum == -1)
+	if (res->start == -1)
 		return AE_ERROR;
-	*bus = busnum;
 	return AE_OK;
 }
 
@@ -429,34 +429,47 @@ static int __devinit acpi_pci_root_add(struct acpi_device *device)
 	struct acpi_device *child;
 	u32 flags, base_flags;
 
+	root = kzalloc(sizeof(struct acpi_pci_root), GFP_KERNEL);
+	if (!root)
+		return -ENOMEM;
+
 	segment = 0;
 	status = acpi_evaluate_integer(device->handle, METHOD_NAME__SEG, NULL,
 				       &segment);
 	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
 		printk(KERN_ERR PREFIX "can't evaluate _SEG\n");
-		return -ENODEV;
+		result = -ENODEV;
+		goto end;
 	}
 
 	/* Check _CRS first, then _BBN.  If no _BBN, default to zero. */
-	bus = 0;
-	status = try_get_root_bridge_busnr(device->handle, &bus);
+	root->secondary.flags = IORESOURCE_BUS;
+	status = try_get_root_bridge_busnr(device->handle, &root->secondary);
 	if (ACPI_FAILURE(status)) {
+		/*
+		 * We need both the start and end of the downstream bus range
+		 * to interpret _CBA (MMCONFIG base address), so it really is
+		 * supposed to be in _CRS.  If we don't find it there, all we
+		 * can do is assume [_BBN-0xFF] or [0-0xFF].
+		 */
+		root->secondary.end = 0xFF;
+		printk(KERN_WARNING FW_BUG PREFIX
+		       "no secondary bus range in _CRS\n");
 		status = acpi_evaluate_integer(device->handle, METHOD_NAME__BBN,					       NULL, &bus);
-		if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
-			printk(KERN_ERR PREFIX
-			     "no bus number in _CRS and can't evaluate _BBN\n");
-			return -ENODEV;
+		if (ACPI_SUCCESS(status))
+			root->secondary.start = bus;
+		else if (status == AE_NOT_FOUND)
+			root->secondary.start = 0;
+		else {
+			printk(KERN_ERR PREFIX "can't evaluate _BBN\n");
+			result = -ENODEV;
+			goto end;
 		}
 	}
 
-	root = kzalloc(sizeof(struct acpi_pci_root), GFP_KERNEL);
-	if (!root)
-		return -ENOMEM;
-
 	INIT_LIST_HEAD(&root->node);
 	root->device = device;
 	root->segment = segment & 0xFFFF;
-	root->bus_nr = bus & 0xFF;
 	strcpy(acpi_device_name(device), ACPI_PCI_ROOT_DEVICE_NAME);
 	strcpy(acpi_device_class(device), ACPI_PCI_ROOT_CLASS);
 	device->driver_data = root;
@@ -475,9 +488,9 @@ static int __devinit acpi_pci_root_add(struct acpi_device *device)
 	/* TBD: Locking */
 	list_add_tail(&root->node, &acpi_pci_roots);
 
-	printk(KERN_INFO PREFIX "%s [%s] (%04x:%02x)\n",
+	printk(KERN_INFO PREFIX "%s [%s] (domain %04x %pR)\n",
 	       acpi_device_name(device), acpi_device_bid(device),
-	       root->segment, root->bus_nr);
+	       root->segment, &root->secondary);
 
 	/*
 	 * Scan the Root Bridge
@@ -486,11 +499,11 @@ static int __devinit acpi_pci_root_add(struct acpi_device *device)
 	 * PCI namespace does not get created until this call is made (and 
 	 * thus the root bridge's pci_dev does not exist).
 	 */
-	root->bus = pci_acpi_scan_root(device, segment, bus);
+	root->bus = pci_acpi_scan_root(root);
 	if (!root->bus) {
 		printk(KERN_ERR PREFIX
 			    "Bus %04x:%02x not present in PCI namespace\n",
-			    root->segment, root->bus_nr);
+			    root->segment, (unsigned int)root->secondary.start);
 		result = -ENODEV;
 		goto end;
 	}
diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
index 7bf83ddf82e0..baacd98e7cc6 100644
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -373,7 +373,7 @@ struct acpi_pci_root {
 	struct acpi_pci_id id;
 	struct pci_bus *bus;
 	u16 segment;
-	u8 bus_nr;
+	struct resource secondary;	/* downstream bus range */
 
 	u32 osc_support_set;	/* _OSC state of support bits */
 	u32 osc_control_set;	/* _OSC state of control bits */
diff --git a/include/acpi/acpi_drivers.h b/include/acpi/acpi_drivers.h
index 4f7b44866b76..23d78b4d088b 100644
--- a/include/acpi/acpi_drivers.h
+++ b/include/acpi/acpi_drivers.h
@@ -104,8 +104,7 @@ int acpi_pci_bind_root(struct acpi_device *device);
 
 /* Arch-defined function to add a bus to the system */
 
-struct pci_bus *pci_acpi_scan_root(struct acpi_device *device, int domain,
-				   int bus);
+struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root);
 void pci_acpi_crs_quirks(void);
 
 /* --------------------------------------------------------------------------