Index: sys/dev/usb/serial/u3g.c
===================================================================
--- sys/dev/usb/serial/u3g.c
+++ sys/dev/usb/serial/u3g.c
@@ -991,8 +991,8 @@
 	}
 	sc->sc_numports = nports;
 
-	error = ucom_attach(&sc->sc_super_ucom, sc->sc_ucom,
-	    sc->sc_numports, sc, &u3g_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, sc->sc_ucom,
+	    sc->sc_numports, sc, &u3g_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		DPRINTF("ucom_attach failed\n");
 		goto detach;
Index: sys/dev/usb/serial/uark.c
===================================================================
--- sys/dev/usb/serial/uark.c
+++ sys/dev/usb/serial/uark.c
@@ -225,8 +225,8 @@
 	usbd_xfer_set_stall(sc->sc_xfer[UARK_BULK_DT_RD]);
 	mtx_unlock(&sc->sc_mtx);
 
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &uark_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &uark_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		DPRINTF("ucom_attach failed\n");
 		goto detach;
Index: sys/dev/usb/serial/ubsa.c
===================================================================
--- sys/dev/usb/serial/ubsa.c
+++ sys/dev/usb/serial/ubsa.c
@@ -324,8 +324,8 @@
 	usbd_xfer_set_stall(sc->sc_xfer[UBSA_BULK_DT_RD]);
 	mtx_unlock(&sc->sc_mtx);
 
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &ubsa_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &ubsa_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		DPRINTF("ucom_attach failed\n");
 		goto detach;
Index: sys/dev/usb/serial/ubser.c
===================================================================
--- sys/dev/usb/serial/ubser.c
+++ sys/dev/usb/serial/ubser.c
@@ -285,8 +285,8 @@
 		sc->sc_ucom[n].sc_portno = n;
 	}
 
-	error = ucom_attach(&sc->sc_super_ucom, sc->sc_ucom,
-	    sc->sc_numser, sc, &ubser_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, sc->sc_ucom,
+	    sc->sc_numser, sc, &ubser_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		goto detach;
 	}
Index: sys/dev/usb/serial/uchcom.c
===================================================================
--- sys/dev/usb/serial/uchcom.c
+++ sys/dev/usb/serial/uchcom.c
@@ -354,8 +354,8 @@
 	usbd_xfer_set_stall(sc->sc_xfer[UCHCOM_BULK_DT_RD]);
 	mtx_unlock(&sc->sc_mtx);
 
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &uchcom_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &uchcom_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		goto detach;
 	}
Index: sys/dev/usb/serial/ucycom.c
===================================================================
--- sys/dev/usb/serial/ucycom.c
+++ sys/dev/usb/serial/ucycom.c
@@ -272,8 +272,8 @@
 		    "transfers failed\n");
 		goto detach;
 	}
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &ucycom_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &ucycom_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		goto detach;
 	}
Index: sys/dev/usb/serial/ufoma.c
===================================================================
--- sys/dev/usb/serial/ufoma.c
+++ sys/dev/usb/serial/ufoma.c
@@ -445,8 +445,8 @@
 	usbd_xfer_set_stall(sc->sc_bulk_xfer[UFOMA_BULK_ENDPT_READ]);
 	mtx_unlock(&sc->sc_mtx);
 
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &ufoma_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &ufoma_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		DPRINTF("ucom_attach failed\n");
 		goto detach;
Index: sys/dev/usb/serial/uftdi.c
===================================================================
--- sys/dev/usb/serial/uftdi.c
+++ sys/dev/usb/serial/uftdi.c
@@ -1129,8 +1129,8 @@
 	/* Indicate tx bits in sc_lsr can be used to determine busy vs idle. */
 	ucom_use_lsr_txbits(&sc->sc_ucom);
 
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &uftdi_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &uftdi_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		goto detach;
 	}
Index: sys/dev/usb/serial/ugensa.c
===================================================================
--- sys/dev/usb/serial/ugensa.c
+++ sys/dev/usb/serial/ugensa.c
@@ -251,8 +251,8 @@
 	}
 	device_printf(dev, "Found %d serial ports.\n", sc->sc_nports);
 
-	error = ucom_attach(&sc->sc_super_ucom, sc->sc_ucom, sc->sc_nports, sc,
-	    &ugensa_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, sc->sc_ucom, sc->sc_nports, sc,
+	    &ugensa_callback, &sc->sc_mtx, uaa->device);
 
 	if (error) {
 		DPRINTF("ucom attach failed\n");
Index: sys/dev/usb/serial/uipaq.c
===================================================================
--- sys/dev/usb/serial/uipaq.c
+++ sys/dev/usb/serial/uipaq.c
@@ -1162,8 +1162,8 @@
 	usbd_xfer_set_stall(sc->sc_xfer[UIPAQ_BULK_DT_RD]);
 	mtx_unlock(&sc->sc_mtx);
 
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &uipaq_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &uipaq_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		goto detach;
 	}
Index: sys/dev/usb/serial/umcs.c
===================================================================
--- sys/dev/usb/serial/umcs.c
+++ sys/dev/usb/serial/umcs.c
@@ -387,8 +387,8 @@
 	}
 	mtx_unlock(&sc->sc_mtx);
 
-	error = ucom_attach(&sc->sc_super_ucom, sc->sc_ucom, sc->sc_numports, sc,
-	    &umcs7840_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, sc->sc_ucom, sc->sc_numports, sc,
+	    &umcs7840_callback, &sc->sc_mtx, uaa->device);
 	if (error)
 		goto detach;
 
Index: sys/dev/usb/serial/umct.c
===================================================================
--- sys/dev/usb/serial/umct.c
+++ sys/dev/usb/serial/umct.c
@@ -303,8 +303,8 @@
 			sc->sc_obufsize = 16;
 		}
 	}
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &umct_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &umct_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		goto detach;
 	}
Index: sys/dev/usb/serial/umodem.c
===================================================================
--- sys/dev/usb/serial/umodem.c
+++ sys/dev/usb/serial/umodem.c
@@ -459,8 +459,8 @@
 
 	ucom_set_usb_mode(&sc->sc_super_ucom, uaa->usb_mode);
 
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &umodem_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &umodem_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		device_printf(dev, "Can't attach com\n");
 		goto detach;
Index: sys/dev/usb/serial/umoscom.c
===================================================================
--- sys/dev/usb/serial/umoscom.c
+++ sys/dev/usb/serial/umoscom.c
@@ -337,8 +337,8 @@
 	usbd_xfer_set_stall(sc->sc_xfer[UMOSCOM_BULK_DT_RD]);
 	mtx_unlock(&sc->sc_mtx);
 
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &umoscom_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &umoscom_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		goto detach;
 	}
Index: sys/dev/usb/serial/uplcom.c
===================================================================
--- sys/dev/usb/serial/uplcom.c
+++ sys/dev/usb/serial/uplcom.c
@@ -484,8 +484,8 @@
 		}
 	}
 
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &uplcom_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &uplcom_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		goto detach;
 	}
Index: sys/dev/usb/serial/usb_serial.h
===================================================================
--- sys/dev/usb/serial/usb_serial.h
+++ sys/dev/usb/serial/usb_serial.h
@@ -211,6 +211,10 @@
 int	ucom_attach(struct ucom_super_softc *,
 	    struct ucom_softc *, int, void *,
 	    const struct ucom_callback *callback, struct mtx *);
+int	ucom_attach_usb(struct ucom_super_softc *,
+	    struct ucom_softc *, int, void *,
+	    const struct ucom_callback *callback, struct mtx *,
+	    struct usb_device *);
 void	ucom_detach(struct ucom_super_softc *, struct ucom_softc *);
 void	ucom_set_pnpinfo_usb(struct ucom_super_softc *, device_t);
 void	ucom_set_usb_mode(struct ucom_super_softc *, enum usb_hc_mode);
Index: sys/dev/usb/serial/usb_serial.c
===================================================================
--- sys/dev/usb/serial/usb_serial.c
+++ sys/dev/usb/serial/usb_serial.c
@@ -92,6 +92,7 @@
 #include <dev/usb/usb_debug.h>
 #include <dev/usb/usb_busdma.h>
 #include <dev/usb/usb_process.h>
+#include <dev/usb/usb_util.h>
 
 #include <dev/usb/serial/usb_serial.h>
 
@@ -111,6 +112,12 @@
     &ucom_device_mode_console, 0,
     "set to 1 to mark terminals as consoles when in device mode");
 
+static int ucom_location_as_unit;
+
+SYSCTL_INT(_hw_usb_ucom, OID_AUTO, location_as_unit, CTLFLAG_RDTUN,
+    &ucom_location_as_unit, 0,
+    "set to 1 to use device location as device unit");
+
 #ifdef USB_DEBUG
 static int ucom_debug = 0;
 
@@ -248,7 +255,7 @@
 {
 	/* sanity checks */
 	if (unit < 0 || unit >= UCOM_UNIT_MAX || ucom_unrhdr == NULL) {
-		DPRINTF("cannot free unit number\n");
+		DPRINTF("cannot free unit %d\n", unit);
 		return;
 	}
 	DPRINTF("unit %d is freed\n", unit);
@@ -267,6 +274,16 @@
     int subunits, void *parent,
     const struct ucom_callback *callback, struct mtx *mtx)
 {
+
+	return (ucom_attach_usb(ssc, sc, subunits, parent, callback, mtx, NULL));
+}
+
+int
+ucom_attach_usb(struct ucom_super_softc *ssc, struct ucom_softc *sc,
+    int subunits, void *parent,
+    const struct ucom_callback *callback, struct mtx *mtx,
+    struct usb_device *udev)
+{
 	int subunit;
 	int error = 0;
 
@@ -278,7 +295,16 @@
 	}
 
 	/* allocate a uniq unit number */
-	ssc->sc_unit = ucom_unit_alloc();
+	if (ucom_location_as_unit == 0 || udev == NULL) {
+		ssc->sc_unit = ucom_unit_alloc();
+	} else {
+		ssc->sc_unit = usb_compute_uniq_location(udev) + UCOM_UNIT_MAX;
+
+		/* add fallback code just in case */
+		if (ssc->sc_unit < UCOM_UNIT_MAX)
+			ssc->sc_unit = ucom_unit_alloc();
+		DPRINTF("unit %d by location\n", location);
+	}
 	if (ssc->sc_unit == -1)
 		return (ENOMEM);
 
Index: sys/dev/usb/serial/uslcom.c
===================================================================
--- sys/dev/usb/serial/uslcom.c
+++ sys/dev/usb/serial/uslcom.c
@@ -447,8 +447,8 @@
 
 	sc->sc_partnum = uslcom_get_partnum(sc);
 
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &uslcom_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &uslcom_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		goto detach;
 	}
Index: sys/dev/usb/serial/uvisor.c
===================================================================
--- sys/dev/usb/serial/uvisor.c
+++ sys/dev/usb/serial/uvisor.c
@@ -348,8 +348,8 @@
 		goto detach;
 	}
 
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &uvisor_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &uvisor_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		DPRINTF("ucom_attach failed\n");
 		goto detach;
Index: sys/dev/usb/serial/uvscom.c
===================================================================
--- sys/dev/usb/serial/uvscom.c
+++ sys/dev/usb/serial/uvscom.c
@@ -322,8 +322,8 @@
 	usbd_xfer_set_stall(sc->sc_xfer[UVSCOM_BULK_DT_RD]);
 	mtx_unlock(&sc->sc_mtx);
 
-	error = ucom_attach(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
-	    &uvscom_callback, &sc->sc_mtx);
+	error = ucom_attach_usb(&sc->sc_super_ucom, &sc->sc_ucom, 1, sc,
+	    &uvscom_callback, &sc->sc_mtx, uaa->device);
 	if (error) {
 		goto detach;
 	}
Index: sys/dev/usb/usb_util.h
===================================================================
--- sys/dev/usb/usb_util.h
+++ sys/dev/usb/usb_util.h
@@ -32,5 +32,6 @@
 uint8_t	usb_make_str_desc(void *ptr, uint16_t max_len, const char *s);
 void	usb_printbcd(char *p, uint16_t p_len, uint16_t bcd);
 void	usb_trim_spaces(char *p);
+int	usb_compute_uniq_location(const struct usb_device *);
 
 #endif					/* _USB_UTIL_H_ */
Index: sys/dev/usb/usb_util.c
===================================================================
--- sys/dev/usb/usb_util.c
+++ sys/dev/usb/usb_util.c
@@ -61,6 +61,8 @@
 
 #include <dev/usb/usb_controller.h>
 #include <dev/usb/usb_bus.h>
+
+#include <dev/usb/usb_hub.h>
 #endif			/* USB_GLOBAL_INCLUDE_FILE */
 
 /*------------------------------------------------------------------------*
@@ -223,3 +225,45 @@
 	}
 	return (totlen);
 }
+
+/*------------------------------------------------------------------------*
+ *	Compute uniq location value for the given USB device
+ *
+ * This function returns a uniq integer value for the given USB
+ * device, based on the location of the USB device. This function
+ * returns -1 if the location doesn't fit into an integer.
+ *------------------------------------------------------------------------*/
+int
+usb_compute_uniq_location(const struct usb_device *udev)
+{
+	int64_t retval;
+	int unit;
+
+	retval = 0;
+
+	unit = device_get_unit(udev->bus->bdev);
+
+	/* range check */
+	if (unit < 0 || unit >= 128)
+		return (-1);
+
+	for (; udev != NULL; udev = udev->parent_hub) {
+		if (udev->hub == NULL)
+			continue;
+		retval *= udev->hub->nports;
+		retval += udev->port_no - 1;
+
+		/* check for overflow */
+		if ((int)retval != retval)
+			return (-1);
+	}
+
+	retval *= 128;
+	retval += unit;
+
+	/* check for overflow */
+	if ((int)retval != retval)
+		return (-1);
+
+	return (retval);
+}