1 files changed, 77 insertions, 5 deletions

diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index 7f0af0e9b826..003170ea2e39 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -64,6 +64,77 @@ void pci_bus_remove_resources(struct pci_bus *bus)
 	}
 }
 
+static bool pci_bus_resource_better(struct resource *res1, bool pos1,
+				    struct resource *res2, bool pos2)
+{
+	/* If exactly one is positive decode, always prefer that one */
+	if (pos1 != pos2)
+		return pos1 ? true : false;
+
+	/* Prefer the one that contains the highest address */
+	if (res1->end != res2->end)
+		return (res1->end > res2->end) ? true : false;
+
+	/* Otherwise, prefer the one with highest "center of gravity" */
+	if (res1->start != res2->start)
+		return (res1->start > res2->start) ? true : false;
+
+	/* Otherwise, choose one arbitrarily (but consistently) */
+	return (res1 > res2) ? true : false;
+}
+
+static bool pci_bus_resource_positive(struct pci_bus *bus, struct resource *res)
+{
+	struct pci_bus_resource *bus_res;
+
+	/*
+	 * This relies on the fact that pci_bus.resource[] refers to P2P or
+	 * CardBus bridge base/limit registers, which are always positively
+	 * decoded.  The pci_bus.resources list contains host bridge or
+	 * subtractively decoded resources.
+	 */
+	list_for_each_entry(bus_res, &bus->resources, list) {
+		if (bus_res->res == res)
+			return (bus_res->flags & PCI_SUBTRACTIVE_DECODE) ?
+				false : true;
+	}
+	return true;
+}
+
+/*
+ * Find the next-best bus resource after the cursor "res".  If the cursor is
+ * NULL, return the best resource.  "Best" means that we prefer positive
+ * decode regions over subtractive decode, then those at higher addresses.
+ */
+static struct resource *pci_bus_find_resource_prev(struct pci_bus *bus,
+						   unsigned int type,
+						   struct resource *res)
+{
+	bool res_pos, r_pos, prev_pos = false;
+	struct resource *r, *prev = NULL;
+	int i;
+
+	res_pos = pci_bus_resource_positive(bus, res);
+	pci_bus_for_each_resource(bus, r, i) {
+		if (!r)
+			continue;
+
+		if ((r->flags & IORESOURCE_TYPE_BITS) != type)
+			continue;
+
+		r_pos = pci_bus_resource_positive(bus, r);
+		if (!res || pci_bus_resource_better(res, res_pos, r, r_pos)) {
+			if (!prev || pci_bus_resource_better(r, r_pos,
+							     prev, prev_pos)) {
+				prev = r;
+				prev_pos = r_pos;
+			}
+		}
+	}
+
+	return prev;
+}
+
 /**
  * pci_bus_alloc_resource - allocate a resource from a parent bus
  * @bus: PCI bus
@@ -89,9 +160,10 @@ pci_bus_alloc_resource(struct pci_bus *bus, struct resource *res,
 					  resource_size_t),
 		void *alignf_data)
 {
-	int i, ret = -ENOMEM;
+	int ret = -ENOMEM;
 	struct resource *r;
 	resource_size_t max = -1;
+	unsigned int type = res->flags & IORESOURCE_TYPE_BITS;
 
 	type_mask |= IORESOURCE_IO | IORESOURCE_MEM;
 
@@ -99,10 +171,9 @@ pci_bus_alloc_resource(struct pci_bus *bus, struct resource *res,
 	if (!(res->flags & IORESOURCE_MEM_64))
 		max = PCIBIOS_MAX_MEM_32;
 
-	pci_bus_for_each_resource(bus, r, i) {
-		if (!r)
-			continue;
-
+	/* Look for space at highest addresses first */
+	r = pci_bus_find_resource_prev(bus, type, NULL);
+	for ( ; r; r = pci_bus_find_resource_prev(bus, type, r)) {
 		/* type_mask must match */
 		if ((res->flags ^ r->flags) & type_mask)
 			continue;
@@ -299,6 +370,7 @@ void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
 	}
 	up_read(&pci_bus_sem);
 }
+EXPORT_SYMBOL_GPL(pci_walk_bus);
 
 EXPORT_SYMBOL(pci_bus_alloc_resource);
 EXPORT_SYMBOL_GPL(pci_bus_add_device);