diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index b5f9f57f436a..f279826204eb 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -752,24 +752,32 @@ static void pci_bridge_check_ranges(struct pci_bus *bus)
 }
 
 /*
- * Helper function for sizing routines: find first available bus resource
- * of a given type.  Note: we intentionally skip the bus resources which
- * have already been assigned (that is, have non-NULL parent resource).
+ * Helper function for sizing routines.  Assigned resources have non-NULL
+ * parent resource.
+ *
+ * Return first unassigned resource of the correct type.  If there is none,
+ * return first assigned resource of the correct type.  If none of the
+ * above, return NULL.
+ *
+ * Returning an assigned resource of the correct type allows the caller to
+ * distinguish between already assigned and no resource of the correct type.
  */
-static struct resource *find_free_bus_resource(struct pci_bus *bus,
-					       unsigned long type_mask,
-					       unsigned long type)
+static struct resource *find_bus_resource_of_type(struct pci_bus *bus,
+						  unsigned long type_mask,
+						  unsigned long type)
 {
+	struct resource *r, *r_assigned = NULL;
 	int i;
-	struct resource *r;
 
 	pci_bus_for_each_resource(bus, r, i) {
 		if (r == &ioport_resource || r == &iomem_resource)
 			continue;
 		if (r && (r->flags & type_mask) == type && !r->parent)
 			return r;
+		if (r && (r->flags & type_mask) == type && !r_assigned)
+			r_assigned = r;
 	}
-	return NULL;
+	return r_assigned;
 }
 
 static resource_size_t calculate_iosize(resource_size_t size,
@@ -866,8 +874,8 @@ static void pbus_size_io(struct pci_bus *bus, resource_size_t min_size,
 			 struct list_head *realloc_head)
 {
 	struct pci_dev *dev;
-	struct resource *b_res = find_free_bus_resource(bus, IORESOURCE_IO,
-							IORESOURCE_IO);
+	struct resource *b_res = find_bus_resource_of_type(bus, IORESOURCE_IO,
+							   IORESOURCE_IO);
 	resource_size_t size = 0, size0 = 0, size1 = 0;
 	resource_size_t children_add_size = 0;
 	resource_size_t min_align, align;
@@ -875,6 +883,10 @@ static void pbus_size_io(struct pci_bus *bus, resource_size_t min_size,
 	if (!b_res)
 		return;
 
+	/* If resource is already assigned, nothing more to do */
+	if (b_res->parent)
+		return;
+
 	min_align = window_alignment(bus, IORESOURCE_IO);
 	list_for_each_entry(dev, &bus->devices, bus_list) {
 		int i;
@@ -978,7 +990,7 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
 	resource_size_t min_align, align, size, size0, size1;
 	resource_size_t aligns[18]; /* Alignments from 1MB to 128GB */
 	int order, max_order;
-	struct resource *b_res = find_free_bus_resource(bus,
+	struct resource *b_res = find_bus_resource_of_type(bus,
 					mask | IORESOURCE_PREFETCH, type);
 	resource_size_t children_add_size = 0;
 	resource_size_t children_add_align = 0;
@@ -987,6 +999,10 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
 	if (!b_res)
 		return -ENOSPC;
 
+	/* If resource is already assigned, nothing more to do */
+	if (b_res->parent)
+		return 0;
+
 	memset(aligns, 0, sizeof(aligns));
 	max_order = 0;
 	size = 0;