Re: [PATCH] thunderbolt: Assert downstream port reset on shutdown

[Mika Westerberg <mika.westerberg@linux.intel.com>]

Hi,

On Wed, Jun 03, 2026 at 11:31:46PM +0530, Basavaraj Natikar wrote:
> On shutdown the connection manager tears down the switch tree without

router tree

> signalling connected devices. Thunderbolt 3 devices directly connected
> to a USB4 host never receive a disconnect indication and during shutdown
> this can cause polling the dead link for up to 60 seconds. On some
> platforms this behavior leads to a warm reset instead of a shutdown due
> to this timeout.
> 
> Fix this by asserting PORT_CS_19.DPR on each connected downstream port
> before tearing down the switch tree. This drives SBTX low unconditionally

router tree

> (USB4 spec section 6.9), causing the device to detect SBRX low and
> transition to Uninitialized Unplugged state immediately.
> 
> Co-developed-by: Sanath S <Sanath.S@amd.com>
> Signed-off-by: Sanath S <Sanath.S@amd.com>
> Signed-off-by: Basavaraj Natikar <Basavaraj.Natikar@amd.com>
> ---
>  drivers/thunderbolt/switch.c |  2 +-
>  drivers/thunderbolt/tb.c     | 11 +++++++++++
>  drivers/thunderbolt/tb.h     |  1 +
>  3 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/thunderbolt/switch.c b/drivers/thunderbolt/switch.c
> index c2ad58b19e7b..52812908818b 100644
> --- a/drivers/thunderbolt/switch.c
> +++ b/drivers/thunderbolt/switch.c
> @@ -704,7 +704,7 @@ int tb_port_disable(struct tb_port *port)
>  	return __tb_port_enable(port, false);
>  }
>  
> -static int tb_port_reset(struct tb_port *port)
> +int tb_port_reset(struct tb_port *port)
>  {
>  	if (tb_switch_is_usb4(port->sw))
>  		return port->cap_usb4 ? usb4_port_reset(port) : 0;
> diff --git a/drivers/thunderbolt/tb.c b/drivers/thunderbolt/tb.c
> index c69c323e6952..ca57b5181422 100644
> --- a/drivers/thunderbolt/tb.c
> +++ b/drivers/thunderbolt/tb.c
> @@ -2935,6 +2935,7 @@ static void tb_stop(struct tb *tb)
>  	struct tb_cm *tcm = tb_priv(tb);
>  	struct tb_tunnel *tunnel;
>  	struct tb_tunnel *n;
> +	struct tb_port *port;
>  
>  	cancel_delayed_work(&tcm->remove_work);
>  	/* tunnels are only present after everything has been initialized */
> @@ -2948,6 +2949,16 @@ static void tb_stop(struct tb *tb)
>  			tb_tunnel_deactivate(tunnel);
>  		tb_tunnel_put(tunnel);
>  	}
> +	/*
> +	 * Assert DPR to drive SBTX low, signalling disconnect and avoiding
> +	 * ~60 s of link polling before warm reset on shutdown.
> +	 */
> +	tb_switch_for_each_port(tb->root_switch, port) {
> +		if (!tb_port_is_null(port) || !tb_port_has_remote(port))
> +			continue;
> +		if (tb_port_reset(port))
> +			tb_port_dbg(port, "DPR on shutdown failed, continuing\n");
> +	}

But now this tears down the topology also when the driver is unloaded? If
you want to do that in shutdown there is ->shutdown hook for that.

>  	tb_switch_remove(tb->root_switch);
>  	tcm->hotplug_active = false; /* signal tb_handle_hotplug to quit */
>  }
> diff --git a/drivers/thunderbolt/tb.h b/drivers/thunderbolt/tb.h
> index 217c3114bec8..875eb538eacf 100644
> --- a/drivers/thunderbolt/tb.h
> +++ b/drivers/thunderbolt/tb.h
> @@ -1102,6 +1102,7 @@ int tb_port_clear_counter(struct tb_port *port, int counter);
>  int tb_port_unlock(struct tb_port *port);
>  int tb_port_enable(struct tb_port *port);
>  int tb_port_disable(struct tb_port *port);
> +int tb_port_reset(struct tb_port *port);
>  int tb_port_alloc_in_hopid(struct tb_port *port, int hopid, int max_hopid);
>  void tb_port_release_in_hopid(struct tb_port *port, int hopid);
>  int tb_port_alloc_out_hopid(struct tb_port *port, int hopid, int max_hopid);
> -- 
> 2.34.1