thunderbolt: Transition link to asymmetric only when both sides support it

We can transition Gen 4 link to asymmetric only when both sides of the
link support it in the required direction. For this reason make sure
that the downstream adapter also supports asymmetric link before
starting the transition.
Signed-off-by: Gil Fine <gil.fine@linux.intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/tb.c

@@ -1094,8 +1094,9 @@ static int tb_configure_asym(struct tb *tb, struct tb_port *src_port,
 	clx = tb_disable_clx(sw);
 
 	tb_for_each_upstream_port_on_path(src_port, dst_port, up) {
+		struct tb_port *down = tb_switch_downstream_port(up->sw);
+		enum tb_link_width width_up, width_down;
 		int consumed_up, consumed_down;
-		enum tb_link_width width;
 
 		ret = tb_consumed_dp_bandwidth(tb, src_port, dst_port, up,
 					       &consumed_up, &consumed_down);
@@ -1116,7 +1117,8 @@ static int tb_configure_asym(struct tb *tb, struct tb_port *src_port,
 			if (consumed_down + requested_down < asym_threshold)
 				continue;
 
-			width = TB_LINK_WIDTH_ASYM_RX;
+			width_up = TB_LINK_WIDTH_ASYM_RX;
+			width_down = TB_LINK_WIDTH_ASYM_TX;
 		} else {
 			/* Upstream, the opposite of above */
 			if (consumed_down + requested_down >= TB_ASYM_MIN) {
@@ -1126,13 +1128,15 @@ static int tb_configure_asym(struct tb *tb, struct tb_port *src_port,
 			if (consumed_up + requested_up < asym_threshold)
 				continue;
 
-			width = TB_LINK_WIDTH_ASYM_TX;
+			width_up = TB_LINK_WIDTH_ASYM_TX;
+			width_down = TB_LINK_WIDTH_ASYM_RX;
 		}
 
-		if (up->sw->link_width == width)
+		if (up->sw->link_width == width_up)
 			continue;
 
-		if (!tb_port_width_supported(up, width))
+		if (!tb_port_width_supported(up, width_up) ||
+		    !tb_port_width_supported(down, width_down))
 			continue;
 
 		tb_sw_dbg(up->sw, "configuring asymmetric link\n");
@@ -1141,7 +1145,7 @@ static int tb_configure_asym(struct tb *tb, struct tb_port *src_port,
 		 * Here requested + consumed > threshold so we need to
 		 * transtion the link into asymmetric now.
 		 */
-		ret = tb_switch_set_link_width(up->sw, width);
+		ret = tb_switch_set_link_width(up->sw, width_up);
 		if (ret) {
 			tb_sw_warn(up->sw, "failed to set link width\n");
 			break;