1 files changed, 49 insertions, 21 deletions

diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index 5624db8c9ad0..003170ea2e39 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -64,17 +64,57 @@ 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 highest-address bus resource below the cursor "res".  If the
- * cursor is NULL, return the highest resource.
+ * 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;
@@ -82,26 +122,14 @@ static struct resource *pci_bus_find_resource_prev(struct pci_bus *bus,
                 if ((r->flags & IORESOURCE_TYPE_BITS) != type)
                         continue;
 
-                /* If this resource is at or past the cursor, skip it */
-                if (res) {
-                        if (r == res)
-                                continue;
-                        if (r->end > res->end)
-                                continue;
-                        if (r->end == res->end && r->start > res->start)
-                                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;
+                        }
                 }
-
-                if (!prev)
-                        prev = r;
-
-                /*
-                 * A small resource is higher than a large one that ends at
-                 * the same address.
-                 */
-                if (r->end > prev->end ||
-                    (r->end == prev->end && r->start > prev->start))
-                        prev = r;
         }
 
         return prev;