[RFC RESEND PATCH 3/4] hw/pci: Add pci_root_bus_max_bus

[Wang Xingang]

From: Xingang Wang <wangxingang5@huawei.com>

This helps to find max bus number of a root bus.

Signed-off-by: Xingang Wang <wangxingang5@huawei.com>
Signed-off-by: Jiahui Cen <cenjiahui@huawei.com>
---
 hw/pci/pci.c         | 33 +++++++++++++++++++++++++++++++++
 include/hw/pci/pci.h |  1 +
 2 files changed, 34 insertions(+)

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index dc969989c9..ed92ce0971 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -516,6 +516,39 @@ int pci_bus_num(PCIBus *s)
     return PCI_BUS_GET_CLASS(s)->bus_num(s);
 }
 
+int pci_root_bus_max_bus(PCIBus *bus)
+{
+    PCIHostState *host;
+    int max_bus = 0;
+    int type;
+    int devfn;
+
+    if (!pci_bus_is_root(bus)) {
+        return 0;
+    }
+
+    host = PCI_HOST_BRIDGE(BUS(bus)->parent);
+    max_bus = pci_bus_num(host->bus);
+
+    for (devfn = 0; devfn < ARRAY_SIZE(host->bus->devices); devfn++) {
+        PCIDevice *dev = host->bus->devices[devfn];
+
+        if (!dev) {
+            continue;
+        }
+
+        type = dev->config[PCI_HEADER_TYPE] & ~PCI_HEADER_TYPE_MULTI_FUNCTION;
+        if (type == PCI_HEADER_TYPE_BRIDGE) {
+            uint8_t subordinate = dev->config[PCI_SUBORDINATE_BUS];
+            if (subordinate > max_bus) {
+                max_bus = subordinate;
+            }
+        }
+    }
+
+    return max_bus;
+}
+
 int pci_bus_numa_node(PCIBus *bus)
 {
     return PCI_BUS_GET_CLASS(bus)->numa_node(bus);
diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index 1bc231480f..238b91817a 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -449,6 +449,7 @@ static inline PCIBus *pci_get_bus(const PCIDevice *dev)
     return PCI_BUS(qdev_get_parent_bus(DEVICE(dev)));
 }
 int pci_bus_num(PCIBus *s);
+int pci_root_bus_max_bus(PCIBus *bus);
 static inline int pci_dev_bus_num(const PCIDevice *dev)
 {
     return pci_bus_num(pci_get_bus(dev));
-- 
2.19.1