x86/PCI: Add x86_pci_root_bus_node() to look up NUMA node from PCI bus

The AMD early_fill_mp_bus_info() already allocates a struct pci_root_info
for each PCI host bridge it finds, and that structure contains the NUMA
node number.  We don't need to keep the same information in the
mp_bus_to_node[] table.

This adds x86_pci_root_bus_node(), which returns the NUMA node number, or
NUMA_NO_NODE if the node is unknown.

Note that unlike get_mp_bus_to_node(), x86_pci_root_bus_node() only works
for root buses.  For example, if amd_bus.c finds a host bridge on node 1 to
[bus 00-0f], get_mp_bus_to_node() returns 1 for any bus between 00 and 0f,
but x86_pci_root_bus_node() returns 1 for bus 00 and NUMA_NO_NODE for buses
01-0f.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

arch/x86/include/asm/topology.h

@@ -131,6 +131,7 @@ static inline void arch_fix_phys_package_id(int num, u32 slot)
 }
 
 struct pci_bus;
+int x86_pci_root_bus_node(int bus);
 void x86_pci_root_bus_resources(int bus, struct list_head *resources);
 
 #ifdef CONFIG_SMP

arch/x86/pci/bus_numa.c

@@ -20,6 +20,16 @@ static struct pci_root_info *x86_find_pci_root_info(int bus)
 	return NULL;
 }
 
+int x86_pci_root_bus_node(int bus)
+{
+	struct pci_root_info *info = x86_find_pci_root_info(bus);
+
+	if (!info)
+		return NUMA_NO_NODE;
+
+	return info->node;
+}
+
 void x86_pci_root_bus_resources(int bus, struct list_head *resources)
 {
 	struct pci_root_info *info = x86_find_pci_root_info(bus);