diff --git a/sys/dev/thunderbolt/nhi.c b/sys/dev/thunderbolt/nhi.c
--- a/sys/dev/thunderbolt/nhi.c
+++ b/sys/dev/thunderbolt/nhi.c
@@ -415,6 +415,20 @@
 	return (0);
 }
 
+int
+nhi_suspend(struct nhi_softc *sc)
+{
+
+	return (tb_router_suspend(sc->root_rsc));
+}
+
+int
+nhi_resume(struct nhi_softc *sc)
+{
+
+	return (0);
+}
+
 static void
 nhi_memaddr_cb(void *arg, bus_dma_segment_t *segs, int nsegs, int error)
 {
diff --git a/sys/dev/thunderbolt/nhi_pci.c b/sys/dev/thunderbolt/nhi_pci.c
--- a/sys/dev/thunderbolt/nhi_pci.c
+++ b/sys/dev/thunderbolt/nhi_pci.c
@@ -242,15 +242,17 @@
 static int
 nhi_pci_suspend(device_t dev)
 {
+	struct nhi_softc *sc = device_get_softc(dev);
 
-	return (0);
+	return (nhi_suspend(sc));
 }
 
 static int
 nhi_pci_resume(device_t dev)
 {
+	struct nhi_softc *sc = device_get_softc(dev);
 
-	return (0);
+	return (nhi_resume(sc));
 }
 
 static void
diff --git a/sys/dev/thunderbolt/nhi_var.h b/sys/dev/thunderbolt/nhi_var.h
--- a/sys/dev/thunderbolt/nhi_var.h
+++ b/sys/dev/thunderbolt/nhi_var.h
@@ -229,6 +229,8 @@
 void nhi_get_tunables(struct nhi_softc *);
 int nhi_attach(struct nhi_softc *);
 int nhi_detach(struct nhi_softc *);
+int nhi_suspend(struct nhi_softc *);
+int nhi_resume(struct nhi_softc *);
 
 struct nhi_cmd_frame * nhi_alloc_tx_frame(struct nhi_ring_pair *);
 void nhi_free_tx_frame(struct nhi_ring_pair *, struct nhi_cmd_frame *);
diff --git a/sys/dev/thunderbolt/router.c b/sys/dev/thunderbolt/router.c
--- a/sys/dev/thunderbolt/router.c
+++ b/sys/dev/thunderbolt/router.c
@@ -255,6 +255,7 @@
 	sc->ring0 = nsc->ring0;
 	sc->route = route;
 	sc->nsc = nsc;
+	sc->suspended = false;
 
 	mtx_init(&sc->mtx, "tbcfg", "Thunderbolt Router Config", MTX_DEF);
 	TAILQ_INIT(&sc->cmd_queue);
@@ -346,6 +347,90 @@
 	return (0);
 }
 
+int
+tb_router_suspend(struct router_softc *sc)
+{
+	int		err;
+	uint32_t	reg;
+
+	tb_debug(sc, DBG_ROUTER|DBG_EXTRA, "%s called\n", __func__);
+	if (sc->suspended) {
+		tb_debug(sc, DBG_ROUTER|DBG_EXTRA, "Already suspended\n");
+		return (0);
+	}
+
+	/*
+	 * TODO Before we do anything, we've first got to make sure that the
+	 * USB3 hub is in the U3 state, and the PCIe endpoint is in D3.
+	 *
+	 * Also check for "USB4 Port is Configured" to know if we support
+	 * sleep state.
+	 */
+
+	/* First, we've got to set ROUTER_CS_5.SLP (enter sleep). */
+	err = tb_config_router_read(sc, ROUTER_CS_5, 1, &reg);
+	if (err != 0) {
+		tb_debug(sc, DBG_ROUTER, "Cannot read ROUTER_CS5\n");
+		return (err);
+	}
+	/*
+	 * We want to set the enter sleep bit, as well as preventing wake
+	 * events from:
+	 * - Wake on PCIe (WoP).
+	 * - Wake on USB3 (WoU).
+	 * - Wake on DisplayPort (WoD).
+	 */
+	reg |= ROUTER_SLP;
+	reg &= ~(ROUTER_WOP | ROUTER_WOU | ROUTER_WOD);
+	err = tb_config_router_write(sc, ROUTER_CS_5, 1, &reg);
+	if (err != 0) {
+		tb_debug(sc, DBG_ROUTER, "Cannot write to ROUTER_CS5\n");
+		return (err);
+	}
+
+	/*
+	 * The ROUTER_CS_6.SLPR (sleep ready) bit should be set tSetSR after
+	 * we set the SLP bit.  Poll for it to be set.
+	 *
+	 * TODO On a v2 router, we should wait for the ROP_CMPLT notification,
+	 * but in the meantime just polling is also valid.
+	 */
+	pause_sbt("tbrouter", ustosbt(NHI_SLPR_WAIT_US), 0, C_HARDCLOCK);
+	err = tb_config_router_read(sc, ROUTER_CS_6, 1, &reg);
+	if (err != 0) {
+		tb_debug(sc, DBG_ROUTER, "Cannot read ROUTER_CS6\n");
+		return (err);
+	}
+	if ((reg & ROUTER_SLPR) != 0)
+		goto ready;
+	tb_printf(sc, "Sleep ready bit not set after 50 ms after "
+	    "asking to enter sleep, waiting...\n");
+	for (size_t i = 0; i < NHI_SLPR_WAIT_MAX; i++) {
+		pause_sbt("tbrouter", ustosbt(NHI_SLPR_WAIT_US), 0,
+		    C_HARDCLOCK);
+		err = tb_config_router_read(sc, ROUTER_CS_6, 1, &reg);
+		if (err != 0) {
+			tb_debug(sc, DBG_ROUTER, "Cannot read ROUTER_CS6\n");
+			return (err);
+		}
+		if ((reg & ROUTER_SLPR) != 0)
+			goto ready;
+	}
+	tb_printf(sc, "Timed out waiting for the sleep ready bit to be"
+	    "set\n");
+	return (ETIMEDOUT);
+
+ready:
+	tb_printf(sc, "Ready to enter sleep\n");
+	sc->suspended = true;
+	/*
+	 * TODO We must tell the host router to send LT_LRoff on the sideband
+	 * channel of each DFP.  (I thought we weren't allowed to send anything
+	 * on the sideband channel after setting the sleep entry bit?)
+	 */
+	return (0);
+}
+
 static void
 router_get_config_cb(struct router_softc *sc, struct router_command *cmd,
     void *arg)
diff --git a/sys/dev/thunderbolt/router_var.h b/sys/dev/thunderbolt/router_var.h
--- a/sys/dev/thunderbolt/router_var.h
+++ b/sys/dev/thunderbolt/router_var.h
@@ -61,6 +61,7 @@
 	tb_route_t		route;
 	device_t		dev;
 	struct nhi_softc	*nsc;
+	bool			suspended;
 
 	struct mtx		mtx;
 	struct nhi_ring_pair	*ring0;
@@ -101,6 +102,7 @@
 int tb_router_attach(struct router_softc *, tb_route_t);
 int tb_router_attach_root(struct nhi_softc *, tb_route_t);
 int tb_router_detach(struct router_softc *);
+int tb_router_suspend(struct router_softc *);
 int tb_config_read(struct router_softc *, u_int, u_int, u_int, u_int,
     uint32_t *);
 int tb_config_read_polled(struct router_softc *, u_int, u_int, u_int, u_int,