Index: sys/dev/pci/pci_pci.c
===================================================================
--- sys/dev/pci/pci_pci.c
+++ sys/dev/pci/pci_pci.c
@@ -957,6 +957,16 @@
 #endif
 
     /*
+     * Internal bridges in Cavium ThunderX SoC
+     * behave as subtractive, but they are unable
+     * to be identified. Force setting an appropriate
+     * flag.
+     */
+    case 0xa002177d: /* ThunderX */
+	sc->flags |= PCIB_SUBTRACTIVE;
+	break;
+
+    /*
      * The i82380FB mobile docking controller is a PCI-PCI bridge,
      * and it is a subtractive bridge.  However, the ProgIf is wrong
      * so the normal setting of PCIB_SUBTRACTIVE bit doesn't