Index: head/sys/dev/virtio/mmio/virtio_mmio.c
===================================================================
--- head/sys/dev/virtio/mmio/virtio_mmio.c
+++ head/sys/dev/virtio/mmio/virtio_mmio.c
@@ -145,6 +145,7 @@
 	/* Bus interface. */
 	DEVMETHOD(bus_driver_added,		  vtmmio_driver_added),
 	DEVMETHOD(bus_child_detached,		  vtmmio_child_detached),
+	DEVMETHOD(bus_child_pnpinfo_str,	  virtio_child_pnpinfo_str),
 	DEVMETHOD(bus_read_ivar,		  vtmmio_read_ivar),
 	DEVMETHOD(bus_write_ivar,		  vtmmio_write_ivar),
 
@@ -331,6 +332,14 @@
 		break;
 	case VIRTIO_IVAR_VENDOR:
 		*result = vtmmio_read_config_4(sc, VIRTIO_MMIO_VENDOR_ID);
+		break;
+	case VIRTIO_IVAR_SUBVENDOR:
+	case VIRTIO_IVAR_DEVICE:
+		/*
+		 * Dummy value for fields not present in this bus.  Used by
+		 * bus-agnostic virtio_child_pnpinfo_str.
+		 */
+		*result = 0;
 		break;
 	default:
 		return (ENOENT);
Index: head/sys/dev/virtio/pci/virtio_pci.c
===================================================================
--- head/sys/dev/virtio/pci/virtio_pci.c
+++ head/sys/dev/virtio/pci/virtio_pci.c
@@ -200,6 +200,7 @@
 	/* Bus interface. */
 	DEVMETHOD(bus_driver_added,		  vtpci_driver_added),
 	DEVMETHOD(bus_child_detached,		  vtpci_child_detached),
+	DEVMETHOD(bus_child_pnpinfo_str,	  virtio_child_pnpinfo_str),
 	DEVMETHOD(bus_read_ivar,		  vtpci_read_ivar),
 	DEVMETHOD(bus_write_ivar,		  vtpci_write_ivar),
 
Index: head/sys/dev/virtio/virtio.h
===================================================================
--- head/sys/dev/virtio/virtio.h
+++ head/sys/dev/virtio/virtio.h
@@ -81,6 +81,8 @@
 int	 virtio_config_generation(device_t dev);
 int	 virtio_reinit(device_t dev, uint64_t features);
 void	 virtio_reinit_complete(device_t dev);
+int	 virtio_child_pnpinfo_str(device_t busdev, device_t child, char *buf,
+	     size_t buflen);
 
 /*
  * Read/write a variable amount from the device specific (ie, network)
Index: head/sys/dev/virtio/virtio.c
===================================================================
--- head/sys/dev/virtio/virtio.c
+++ head/sys/dev/virtio/virtio.c
@@ -263,6 +263,30 @@
 	    offset, dst, len);
 }
 
+int
+virtio_child_pnpinfo_str(device_t busdev __unused, device_t child, char *buf,
+    size_t buflen)
+{
+
+	/*
+	 * All of these PCI fields will be only 16 bits, but on the vtmmio bus
+	 * the corresponding fields (only "vendor" and "device_type") are 32
+	 * bits.  Many virtio drivers can attach below either bus.
+	 * Gratuitously expand these two fields to 32-bits to allow sharing PNP
+	 * match table data between the mostly-similar buses.
+	 *
+	 * Subdevice and device_type are redundant in both buses, so I don't
+	 * see a lot of PNP utility in exposing the same value under a
+	 * different name.
+	 */
+	snprintf(buf, buflen, "vendor=0x%08x device=0x%04x subvendor=0x%04x "
+	    "device_type=0x%08x", (unsigned)virtio_get_vendor(child),
+	    (unsigned)virtio_get_device(child),
+	    (unsigned)virtio_get_subvendor(child),
+	    (unsigned)virtio_get_device_type(child));
+	return (0);
+}
+
 static int
 virtio_modevent(module_t mod, int type, void *unused)
 {