[PATCH] thunderbolt: Keep link as asymmetric if preferred by hardware

[PATCH] thunderbolt: Keep link as asymmetric if preferred by hardware

[Mika Westerberg]

From: Gil Fine <gil.fine@linux.intel.com>

In case of the link is brought up as asymmetric (due to hardware preference), we
honor that and don't transition it to symmetric, unless a router with symmetric
link got plugged below, in the topology (and a bandwidth allows transition to
symmetric).

Signed-off-by: Gil Fine <gil.fine@linux.intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
---
 drivers/thunderbolt/switch.c | 13 +++++++++++++
 drivers/thunderbolt/tb.c     | 28 +++++++++++++++++++++-------
 drivers/thunderbolt/tb.h     |  2 ++
 3 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/drivers/thunderbolt/switch.c b/drivers/thunderbolt/switch.c
index dbab551ac7b3..900114ba4371 100644
--- a/drivers/thunderbolt/switch.c
+++ b/drivers/thunderbolt/switch.c
@@ -2773,6 +2773,19 @@ static void tb_switch_link_init(struct tb_switch *sw)
 	if (down->dual_link_port)
 		down->dual_link_port->bonded = bonded;
 	tb_port_update_credits(down);
+
+	if (tb_port_get_link_generation(up) < 4)
+		return;
+
+	/*
+	 * Set the Gen 4 preferred link width. This is what the router
+	 * prefers when the link is brought up. If the router does not
+	 * support asymmetric link configuration, this also will be set
+	 * to TB_LINK_WIDTH_DUAL.
+	 */
+	sw->preferred_link_width = sw->link_width;
+	tb_sw_dbg(sw, "preferred link width %s\n",
+		  tb_width_name(sw->preferred_link_width));
 }
 
 /**
diff --git a/drivers/thunderbolt/tb.c b/drivers/thunderbolt/tb.c
index 0a32e7ec4dc0..846d2813bb1a 100644
--- a/drivers/thunderbolt/tb.c
+++ b/drivers/thunderbolt/tb.c
@@ -1183,14 +1183,15 @@ static int tb_configure_asym(struct tb *tb, struct tb_port *src_port,
  * @dst_port: Destination adapter
  * @requested_up: New lower bandwidth request upstream (Mb/s)
  * @requested_down: New lower bandwidth request downstream (Mb/s)
+ * @keep_asym: Keep asymmetric link if preferred
  *
  * Goes over each link from @src_port to @dst_port and tries to
  * transition the link to symmetric if the currently consumed bandwidth
- * allows.
+ * allows and link asymmetric preference is ignored (if @keep_asym is %false).
  */
 static int tb_configure_sym(struct tb *tb, struct tb_port *src_port,
 			    struct tb_port *dst_port, int requested_up,
-			    int requested_down)
+			    int requested_down, bool keep_asym)
 {
 	bool clx = false, clx_disabled = false, downstream;
 	struct tb_switch *sw;
@@ -1239,6 +1240,19 @@ static int tb_configure_sym(struct tb *tb, struct tb_port *src_port,
 		if (up->sw->link_width == TB_LINK_WIDTH_DUAL)
 			continue;
 
+		/*
+		 * Here consumed < threshold so we can transition the
+		 * link to symmetric.
+		 *
+		 * However, if the router prefers asymmetric link we
+		 * honor that (unless @keep_asym is %false).
+		 */
+		if (keep_asym &&
+		    up->sw->preferred_link_width > TB_LINK_WIDTH_DUAL) {
+			tb_sw_dbg(up->sw, "keeping preferred asymmetric link\n");
+			continue;
+		}
+
 		/* Disable CL states before doing any transitions */
 		if (!clx_disabled) {
 			clx = tb_disable_clx(sw);
@@ -1292,7 +1306,7 @@ static void tb_configure_link(struct tb_port *down, struct tb_port *up,
 		struct tb_port *host_port;
 
 		host_port = tb_port_at(tb_route(sw), tb->root_switch);
-		tb_configure_sym(tb, host_port, up, 0, 0);
+		tb_configure_sym(tb, host_port, up, 0, 0, false);
 	}
 
 	/* Set the link configured */
@@ -1477,7 +1491,7 @@ static void tb_deactivate_and_free_tunnel(struct tb_tunnel *tunnel)
 		 * If bandwidth on a link is < asym_threshold
 		 * transition the link to symmetric.
 		 */
-		tb_configure_sym(tb, src_port, dst_port, 0, 0);
+		tb_configure_sym(tb, src_port, dst_port, 0, 0, true);
 		/* Now we can allow the domain to runtime suspend again */
 		pm_runtime_mark_last_busy(&dst_port->sw->dev);
 		pm_runtime_put_autosuspend(&dst_port->sw->dev);
@@ -2299,7 +2313,7 @@ static int tb_alloc_dp_bandwidth(struct tb_tunnel *tunnel, int *requested_up,
 		 * If bandwidth on a link is < asym_threshold transition
 		 * the link to symmetric.
 		 */
-		tb_configure_sym(tb, in, out, *requested_up, *requested_down);
+		tb_configure_sym(tb, in, out, *requested_up, *requested_down, true);
 		/*
 		 * If requested bandwidth is less or equal than what is
 		 * currently allocated to that tunnel we simply change
@@ -2342,7 +2356,7 @@ static int tb_alloc_dp_bandwidth(struct tb_tunnel *tunnel, int *requested_up,
 		ret = tb_configure_asym(tb, in, out, *requested_up,
 					*requested_down);
 		if (ret) {
-			tb_configure_sym(tb, in, out, 0, 0);
+			tb_configure_sym(tb, in, out, 0, 0, true);
 			return ret;
 		}
 
@@ -2350,7 +2364,7 @@ static int tb_alloc_dp_bandwidth(struct tb_tunnel *tunnel, int *requested_up,
 						requested_down);
 		if (ret) {
 			tb_tunnel_warn(tunnel, "failed to allocate bandwidth\n");
-			tb_configure_sym(tb, in, out, 0, 0);
+			tb_configure_sym(tb, in, out, 0, 0, true);
 		}
 	} else {
 		ret = -ENOBUFS;
diff --git a/drivers/thunderbolt/tb.h b/drivers/thunderbolt/tb.h
index 1760c21e5b12..997c5a536905 100644
--- a/drivers/thunderbolt/tb.h
+++ b/drivers/thunderbolt/tb.h
@@ -125,6 +125,7 @@ struct tb_switch_tmu {
  * @device_name: Name of the device (or %NULL if not known)
  * @link_speed: Speed of the link in Gb/s
  * @link_width: Width of the upstream facing link
+ * @preferred_link_width: Router preferred link width (only set for Gen 4 links)
  * @link_usb4: Upstream link is USB4
  * @generation: Switch Thunderbolt generation
  * @cap_plug_events: Offset to the plug events capability (%0 if not found)
@@ -178,6 +179,7 @@ struct tb_switch {
 	const char *device_name;
 	unsigned int link_speed;
 	enum tb_link_width link_width;
+	enum tb_link_width preferred_link_width;
 	bool link_usb4;
 	unsigned int generation;
 	int cap_plug_events;
-- 
2.43.0

Re: [PATCH] thunderbolt: Keep link as asymmetric if preferred by hardware

[Mika Westerberg]

On Tue, Dec 19, 2023 at 09:15:31AM +0200, Mika Westerberg wrote:
> From: Gil Fine <gil.fine@linux.intel.com>
> 
> In case of the link is brought up as asymmetric (due to hardware preference), we
> honor that and don't transition it to symmetric, unless a router with symmetric
> link got plugged below, in the topology (and a bandwidth allows transition to
> symmetric).
> 
> Signed-off-by: Gil Fine <gil.fine@linux.intel.com>
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

Applied to thunderbolt.git/next.