thunderbolt: Disable CL states when a DMA tunnel is established

Tunnels between hosts should not have CL states enabled because
otherwise they might enter a low power state without the other end
noticing which causes packets to be lost. For this reason disable all
CL states upon first DMA tunnel creation. Once the last DMA tunnel is
torn down we try to re-enable them.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/clx.c

@@ -317,7 +317,7 @@ int tb_switch_clx_enable(struct tb_switch *sw, unsigned int clx)
 	struct tb_port *up, *down;
 	int ret;
 
-	if (!clx)
+	if (!clx || sw->clx == clx)
 		return 0;
 
 	if (!validate_mask(clx))

drivers/thunderbolt/tb.c

@@ -240,8 +240,11 @@ static void tb_discover_dp_resources(struct tb *tb)
 	}
 }
 
+/* Enables CL states up to host router */
 static int tb_enable_clx(struct tb_switch *sw)
 {
+	struct tb_cm *tcm = tb_priv(sw->tb);
+	const struct tb_tunnel *tunnel;
 	int ret;
 
 	/*
@@ -251,9 +254,26 @@ static int tb_enable_clx(struct tb_switch *sw)
 	 * this in the future to cover the whole topology if it turns
 	 * out to be beneficial.
 	 */
+	while (sw && sw->config.depth > 1)
+		sw = tb_switch_parent(sw);
+
+	if (!sw)
+		return 0;
+
 	if (sw->config.depth != 1)
 		return 0;
 
+	/*
+	 * If we are re-enabling then check if there is an active DMA
+	 * tunnel and in that case bail out.
+	 */
+	list_for_each_entry(tunnel, &tcm->tunnel_list, list) {
+		if (tb_tunnel_is_dma(tunnel)) {
+			if (tb_tunnel_port_on_path(tunnel, tb_upstream_port(sw)))
+				return 0;
+		}
+	}
+
 	/*
 	 * CL0s and CL1 are enabled and supported together.
 	 * Silently ignore CLx enabling in case CLx is not supported.
@@ -262,6 +282,16 @@ static int tb_enable_clx(struct tb_switch *sw)
 	return ret == -EOPNOTSUPP ? 0 : ret;
 }
 
+/* Disables CL states up to the host router */
+static void tb_disable_clx(struct tb_switch *sw)
+{
+	do {
+		if (tb_switch_clx_disable(sw) < 0)
+			tb_sw_warn(sw, "failed to disable CL states\n");
+		sw = tb_switch_parent(sw);
+	} while (sw);
+}
+
 static int tb_increase_switch_tmu_accuracy(struct device *dev, void *data)
 {
 	struct tb_switch *sw;
@@ -1470,30 +1500,45 @@ static int tb_approve_xdomain_paths(struct tb *tb, struct tb_xdomain *xd,
 	struct tb_port *nhi_port, *dst_port;
 	struct tb_tunnel *tunnel;
 	struct tb_switch *sw;
+	int ret;
 
 	sw = tb_to_switch(xd->dev.parent);
 	dst_port = tb_port_at(xd->route, sw);
 	nhi_port = tb_switch_find_port(tb->root_switch, TB_TYPE_NHI);
 
 	mutex_lock(&tb->lock);
+
+	/*
+	 * When tunneling DMA paths the link should not enter CL states
+	 * so disable them now.
+	 */
+	tb_disable_clx(sw);
+
 	tunnel = tb_tunnel_alloc_dma(tb, nhi_port, dst_port, transmit_path,
 				     transmit_ring, receive_path, receive_ring);
 	if (!tunnel) {
-		mutex_unlock(&tb->lock);
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto err_clx;
 	}
 
 	if (tb_tunnel_activate(tunnel)) {
 		tb_port_info(nhi_port,
 			     "DMA tunnel activation failed, aborting\n");
-		tb_tunnel_free(tunnel);
-		mutex_unlock(&tb->lock);
-		return -EIO;
+		ret = -EIO;
+		goto err_free;
 	}
 
 	list_add_tail(&tunnel->list, &tcm->tunnel_list);
 	mutex_unlock(&tb->lock);
 	return 0;
+
+err_free:
+	tb_tunnel_free(tunnel);
+err_clx:
+	tb_enable_clx(sw);
+	mutex_unlock(&tb->lock);
+
+	return ret;
 }
 
 static void __tb_disconnect_xdomain_paths(struct tb *tb, struct tb_xdomain *xd,
@@ -1519,6 +1564,13 @@ static void __tb_disconnect_xdomain_paths(struct tb *tb, struct tb_xdomain *xd,
 					receive_path, receive_ring))
 			tb_deactivate_and_free_tunnel(tunnel);
 	}
+
+	/*
+	 * Try to re-enable CL states now, it is OK if this fails
+	 * because we may still have another DMA tunnel active through
+	 * the same host router USB4 downstream port.
+	 */
+	tb_enable_clx(sw);
 }
 
 static int tb_disconnect_xdomain_paths(struct tb *tb, struct tb_xdomain *xd,