[Qemu-devel] [PATCH v1 1/2] s390x/pci: Fix primary bus number for PCI bridges

[David Hildenbrand <david@redhat.com>]

The primary bus number corresponds always to the bus number of the
bus the bridge is attached to.

Right now, if we have two bridges attached to the same bus (e.g. root
bus) this is however not the case. Fix assignment.

While at it
- Add a comment why we have to reassign durign every reset (which I
  found to be supprising)
- Drop setting the PCI_SUBORDINATE_BUS temporarily to 0xff. As we are
  setting it via a DFS and not via a BFS (as discussed e.g. in [1]), this
  is not necessary. The last number when we return is the highest
  number.

Please note that hotplugging of bridges is in general still broken, will
be fixed next.

[1] http://www.science.unitn.it/~fiorella/guidelinux/tlk/node76.html

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 hw/s390x/s390-pci-bus.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
index f017c1ded0..b7c4613fde 100644
--- a/hw/s390x/s390-pci-bus.c
+++ b/hw/s390x/s390-pci-bus.c
@@ -862,7 +862,8 @@ static void s390_pcihost_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
         qbus_set_hotplug_handler(bus, DEVICE(s), errp);
 
         if (dev->hotplugged) {
-            pci_default_write_config(pdev, PCI_PRIMARY_BUS, s->bus_no, 1);
+            pci_default_write_config(pdev, PCI_PRIMARY_BUS,
+                                     pci_dev_bus_num(pdev), 1);
             s->bus_no += 1;
             pci_default_write_config(pdev, PCI_SECONDARY_BUS, s->bus_no, 1);
             do {
@@ -1016,8 +1017,6 @@ static void s390_pci_enumerate_bridge(PCIBus *bus, PCIDevice *pdev,
                                       void *opaque)
 {
     S390pciState *s = opaque;
-    unsigned int primary = s->bus_no;
-    unsigned int subordinate = 0xff;
     PCIBus *sec_bus = NULL;
 
     if ((pci_default_read_config(pdev, PCI_HEADER_TYPE, 1) !=
@@ -1026,7 +1025,7 @@ static void s390_pci_enumerate_bridge(PCIBus *bus, PCIDevice *pdev,
     }
 
     (s->bus_no)++;
-    pci_default_write_config(pdev, PCI_PRIMARY_BUS, primary, 1);
+    pci_default_write_config(pdev, PCI_PRIMARY_BUS, pci_dev_bus_num(pdev), 1);
     pci_default_write_config(pdev, PCI_SECONDARY_BUS, s->bus_no, 1);
     pci_default_write_config(pdev, PCI_SUBORDINATE_BUS, s->bus_no, 1);
 
@@ -1035,7 +1034,7 @@ static void s390_pci_enumerate_bridge(PCIBus *bus, PCIDevice *pdev,
         return;
     }
 
-    pci_default_write_config(pdev, PCI_SUBORDINATE_BUS, subordinate, 1);
+    /* Assign numbers to all child bridges. The last is the highest number. */
     pci_for_each_device(sec_bus, pci_bus_num(sec_bus),
                         s390_pci_enumerate_bridge, s);
     pci_default_write_config(pdev, PCI_SUBORDINATE_BUS, s->bus_no, 1);
@@ -1046,6 +1045,10 @@ static void s390_pcihost_reset(DeviceState *dev)
     S390pciState *s = S390_PCI_HOST_BRIDGE(dev);
     PCIBus *bus = s->parent_obj.bus;
 
+    /*
+     * When resetting a PCI bridge, the assigned numbers are set to 0. So
+     * on every system reset, we also have to reassign numbers.
+     */
     s->bus_no = 0;
     pci_for_each_device(bus, pci_bus_num(bus), s390_pci_enumerate_bridge, s);
 }
-- 
2.17.2