OvmfPkg/PciHostBridgeLib: Scan for root bridges when running over Xen

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Gary Lin <glin@suse.com>

OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c

@@ -28,6 +28,7 @@
 #include <Library/PciHostBridgeLib.h>
 #include <Library/PciLib.h>
 #include <Library/QemuFwCfgLib.h>
+#include "PciHostBridge.h"
 
 
 #pragma pack(1)
@@ -113,7 +114,6 @@ STATIC PCI_ROOT_BRIDGE_APERTURE mNonExistAperture = { MAX_UINT64, 0 };
 
   @retval EFI_OUT_OF_RESOURCES  Memory allocation failed.
 **/
-STATIC
 EFI_STATUS
 InitRootBridge (
   IN  UINT64                   Supports,
@@ -217,6 +217,10 @@ PciHostBridgeGetRootBridges (
   PCI_ROOT_BRIDGE_APERTURE Mem;
   PCI_ROOT_BRIDGE_APERTURE MemAbove4G;
 
+  if (PcdGetBool (PcdPciDisableBusEnumeration)) {
+    return ScanForRootBridges (Count);
+  }
+
   Attributes = EFI_PCI_ATTRIBUTE_IDE_PRIMARY_IO |
     EFI_PCI_ATTRIBUTE_IDE_SECONDARY_IO |
     EFI_PCI_ATTRIBUTE_ISA_IO_16 |