1 files changed, 11 insertions, 2 deletions

diff --git a/arch/x86_64/kernel/pci-calgary.c b/arch/x86_64/kernel/pci-calgary.c
index 1100031528dc..3c0c7fde09d8 100644
--- a/arch/x86_64/kernel/pci-calgary.c
+++ b/arch/x86_64/kernel/pci-calgary.c
@@ -790,7 +790,16 @@ static inline unsigned int __init locate_register_space(struct pci_dev *dev)
         int rionodeid;
         u32 address;
 
-        rionodeid = (dev->bus->number % 15 > 4) ? 3 : 2;
+        /*
+         * Each Calgary has four busses. The first four busses (first Calgary)
+         * have RIO node ID 2, then the next four (second Calgary) have RIO
+         * node ID 3, the next four (third Calgary) have node ID 2 again, etc.
+         * We use a gross hack - relying on the dev->bus->number ordering,
+         * modulo 14 - to decide which Calgary a given bus is on. Busses 0, 1,
+         * 2 and 4 are on the first Calgary (id 2), 6, 8, a and c are on the
+         * second (id 3), and then it repeats modulo 14.
+         */
+        rionodeid = (dev->bus->number % 14 > 4) ? 3 : 2;
         /*
          * register space address calculation as follows:
          * FE0MB-8MB*OneBasedChassisNumber+1MB*(RioNodeId-ChassisBase)
@@ -798,7 +807,7 @@ static inline unsigned int __init locate_register_space(struct pci_dev *dev)
          * RioNodeId is 2 for first Calgary, 3 for second Calgary
          */
         address = START_ADDRESS -
-                (0x800000 * (ONE_BASED_CHASSIS_NUM + dev->bus->number / 15)) +
+                (0x800000 * (ONE_BASED_CHASSIS_NUM + dev->bus->number / 14)) +
                 (0x100000) * (rionodeid - CHASSIS_BASE);
         return address;
 }