Index: sys/dev/pci/pci.c
===================================================================
--- sys/dev/pci/pci.c
+++ sys/dev/pci/pci.c
@@ -6261,11 +6261,9 @@
 pci_find_pcie_root_port(device_t dev)
 {
 	struct pci_devinfo *dinfo;
-	devclass_t pci_class;
 	device_t pcib, bus;
 
-	pci_class = devclass_find("pci");
-	KASSERT(device_get_devclass(device_get_parent(dev)) == pci_class,
+	KASSERT(devclass_is_derived_from("pci", dev),
 	    ("%s: non-pci device %s", __func__, device_get_nameunit(dev)));
 
 	/*
@@ -6285,7 +6283,7 @@
 		 * pcib's parent must be a PCI bus for this to be a
 		 * PCI-PCI bridge.
 		 */
-		if (device_get_devclass(device_get_parent(pcib)) != pci_class)
+		if (!devclass_is_derived_from("pci", device_get_parent(pcib)))
 			return (NULL);
 
 		dinfo = device_get_ivars(pcib);
Index: sys/kern/subr_bus.c
===================================================================
--- sys/kern/subr_bus.c
+++ sys/kern/subr_bus.c
@@ -1755,6 +1755,23 @@
 	return (0);
 }
 
+bool
+devclass_is_derived_from(const char *name, device_t dev)
+{
+	devclass_t dc, ddc;
+
+	dc = devclass_find(name);
+	if (dc == NULL)
+		return (false);
+	ddc = device_get_devclass(dev);
+	while (dc != NULL) {
+		if (dc == ddc)
+			return (true);
+		dc = dc->parent;
+	}
+	return (false);
+}
+
 /**
  * @internal
  * @brief Make a new device and add it as a child of @p parent
Index: sys/sys/bus.h
===================================================================
--- sys/sys/bus.h
+++ sys/sys/bus.h
@@ -652,6 +652,7 @@
 devclass_t	devclass_get_parent(devclass_t dc);
 struct sysctl_ctx_list *devclass_get_sysctl_ctx(devclass_t dc);
 struct sysctl_oid *devclass_get_sysctl_tree(devclass_t dc);
+bool		devclass_is_derived_from(const char *, device_t);
 
 /*
  * Access functions for device resources.