diff --git a/drivers/pci/host-bridge.c b/drivers/pci/host-bridge.c
new file mode 100644
index 0000000..28b24a5
--- /dev/null
+++ b/drivers/pci/host-bridge.c
@@ -0,0 +1,93 @@
+/*
+ * host bridge related code
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/pci.h>
+#include <linux/module.h>
+
+#include "pci.h"
+
+static LIST_HEAD(pci_host_bridges);
+
+void add_to_pci_host_bridges(struct pci_host_bridge *bridge)
+{
+	list_add_tail(&bridge->list, &pci_host_bridges);
+}
+
+static struct pci_host_bridge *pci_host_bridge(struct pci_dev *dev)
+{
+	struct pci_bus *bus;
+	struct pci_host_bridge *bridge;
+
+	bus = dev->bus;
+	while (bus->parent)
+		bus = bus->parent;
+
+	list_for_each_entry(bridge, &pci_host_bridges, list) {
+		if (bridge->bus == bus)
+			return bridge;
+	}
+
+	return NULL;
+}
+
+static bool resource_contains(struct resource *res1, struct resource *res2)
+{
+	return res1->start <= res2->start && res1->end >= res2->end;
+}
+
+void pcibios_resource_to_bus(struct pci_dev *dev, struct pci_bus_region *region,
+			     struct resource *res)
+{
+	struct pci_host_bridge *bridge = pci_host_bridge(dev);
+	struct pci_host_bridge_window *window;
+	resource_size_t offset = 0;
+
+	list_for_each_entry(window, &bridge->windows, list) {
+		if (resource_type(res) != resource_type(window->res))
+			continue;
+
+		if (resource_contains(window->res, res)) {
+			offset = window->offset;
+			break;
+		}
+	}
+
+	region->start = res->start - offset;
+	region->end = res->end - offset;
+}
+EXPORT_SYMBOL(pcibios_resource_to_bus);
+
+static bool region_contains(struct pci_bus_region *region1,
+			    struct pci_bus_region *region2)
+{
+	return region1->start <= region2->start && region1->end >= region2->end;
+}
+
+void pcibios_bus_to_resource(struct pci_dev *dev, struct resource *res,
+			     struct pci_bus_region *region)
+{
+	struct pci_host_bridge *bridge = pci_host_bridge(dev);
+	struct pci_host_bridge_window *window;
+	struct pci_bus_region bus_region;
+	resource_size_t offset = 0;
+
+	list_for_each_entry(window, &bridge->windows, list) {
+		if (resource_type(res) != resource_type(window->res))
+			continue;
+
+		bus_region.start = window->res->start - window->offset;
+		bus_region.end = window->res->end - window->offset;
+
+		if (region_contains(&bus_region, region)) {
+			offset = window->offset;
+			break;
+		}
+	}
+
+	res->start = region->start + offset;
+	res->end = region->end + offset;
+}
+EXPORT_SYMBOL(pcibios_bus_to_resource);