[PATCH V2] pci: fixes to allow booting from extra root pci buses.

[Marcel Apfelbaum]

The fixes solves the following issue:
The PXB device exposes a new  pci root bridge with the
fw path:  /pci-root@4/..., in which 4 is the root bus number.
Before this patch the fw path was wrongly computed:
    /pci-root@1/pci@i0cf8/...
Fix the above issues: Correct the bus number and remove the
extra host bridge description.

The IEEE Std 1275-1994:

IEEE Standard for Boot (Initialization Configuration)
    Firmware: Core Requirements and Practices
      3.2.1.1 Node names
          Each node in the device tree is identified by a node name
          using the following notation:
              driver-name@unit-address:device-arguments

The driver name field is a sequence of between one and 31
          letters [...]. By convention, this name includes the name of
          the device’s manufacturer and the device’s model name separated by
          a “,”.

The unit address field is the text representation of the
          physical address of the device within the address space
          defined by its parent node. The form of the text
          representation is bus-dependent.
    3.2.1.2 Path names
        A particular node is uniquely identified by describing its position
        in the device tree by completely specifying the
        path from the root node through all intermediate nodes to the node
        in question. The textual representation of a
        such a path is called a device path. Device paths are composed as
        follows:
        /node-name0/node-name1/ ... /node-nameN
        When Open Firmware is searching for a particular node, and either
        the driver name or @unit-address portion of
        the node name is not given, Open Firmware shall arbitrarily choose a
        node matching the portion that is present.

Signed-off-by: Marcel Apfelbaum 
---
v1->v2:
  - fixed a bug preventing the boot of devices behind the main host bridge
    This approach leaves previous code paths intact so it will work the same
    as before if no PXB is present.
  - Added spec for fw path naming conventions. (Michael S. Tsirkin)

src/boot.c   | 3 ++-
 src/hw/pci.c | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/boot.c b/src/boot.c
index ec59c37..e241d1c 100644
--- a/src/boot.c
+++ b/src/boot.c
@@ -114,7 +114,8 @@ build_pci_path(char *buf, int max, const char *devname, struct pci_device *pci)
     } else {
         if (pci->rootbus)
             p += snprintf(p, max, "/pci-root@%x", pci->rootbus);
-        p += snprintf(p, buf+max-p, "%s", FW_PCI_DOMAIN);
+        else
+            p += snprintf(p, buf+max-p, "%s", FW_PCI_DOMAIN);
     }

int dev = pci_bdf_to_dev(pci->bdf), fn = pci_bdf_to_fn(pci->bdf);
diff --git a/src/hw/pci.c b/src/hw/pci.c
index 0379b55..9e77af4 100644
--- a/src/hw/pci.c
+++ b/src/hw/pci.c
@@ -133,7 +133,7 @@ pci_probe_devices(void)
                 if (bus != lastbus)
                     rootbuses++;
                 lastbus = bus;
-                rootbus = rootbuses;
+                rootbus = bus;
                 if (bus > MaxPCIBus)
                     MaxPCIBus = bus;
             } else {