x86/PCI: don't fall back to defaults if _CRS has no apertures

Host bridges that lead to things like the Uncore need not have any
I/O port or MMIO apertures.  For example, in this case:

    ACPI: PCI Root Bridge [UNC1] (domain 0000 [bus ff])
    PCI: root bus ff: using default resources
    PCI host bridge to bus 0000:ff
    pci_bus 0000:ff: root bus resource [io  0x0000-0xffff]
    pci_bus 0000:ff: root bus resource [mem 0x00000000-0x3fffffffffff]

we should not pretend those default resources are available on bus ff.

CC: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

arch/x86/pci/acpi.c

@@ -404,7 +404,12 @@ struct pci_bus * __devinit pci_acpi_scan_root(struct acpi_pci_root *root)
 		kfree(sd);
 	} else {
 		get_current_resources(device, busnum, domain, &resources);
-		if (list_empty(&resources))
+
+		/*
+		 * _CRS with no apertures is normal, so only fall back to
+		 * defaults or native bridge info if we're ignoring _CRS.
+		 */
+		if (!pci_use_crs)
 			x86_pci_root_bus_resources(busnum, &resources);
 		bus = pci_create_root_bus(NULL, busnum, &pci_root_ops, sd,
 					  &resources);