Re: [PATCH 14/19] thunderbolt: Add QUIRK_NO_USB3_BW_ALLOC

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

Hi,

On Sun, Aug 30, 2026 at 10:19:32PM +0200, Sven Peter wrote:
> The host routers on Apple Silicon do not implement USB3 bandwidth
> allocation registers: the CMR bit set in ADP_USB3_CS_2 by
> usb4_usb3_port_cm_request() is never acknowledged and every USB3 tunnel
> bringup fails there after the timeout:
> 
>   [   49.259325] thunderbolt-apple-nhi 501f00000.nhi: 1:16: available bandwidth for new USB3 tunnel 18000/18000 Mb/s
>   [   49.265869] thunderbolt-apple-nhi 501f00000.nhi: 1:16: maximum required bandwidth for USB3 tunnel 9000 Mb/s
>   [   49.267894] thunderbolt-apple-nhi 501f00000.nhi: 0:4 <-> 1:16 (USB3): activating
>   [   49.269410] thunderbolt-apple-nhi 501f00000.nhi: 0:4 <-> 1:16 (USB3): allocating initial bandwidth 9000/9000 Mb/s
>   [   50.771764] thunderbolt-apple-nhi 501f00000.nhi: 1:16: USB3 tunnel activation failed, aborting

Okay this kind of makes sense. Apple is doing this only via software and
this is also what Linux needs to do with USB3 Gen T tunneling so we should
prepare for this.

> Add a quirk to skip bandwidth allocation entirely but keep tracking
> the initial allocation in software for the consumed bandwidth
> calculation. For completeness, discovered tunnels book 90% of the
> maximum link rate in software, matching tb_tunnel_alloc_usb3(), although
> Apple Silicon cannot have any pre-existing tunnels.
> 
> Signed-off-by: Sven Peter <sven@kernel.org>
> ---
>  drivers/thunderbolt/nhi.h    |  1 +
>  drivers/thunderbolt/tb.c     |  8 ++++++
>  drivers/thunderbolt/tb.h     |  3 +++
>  drivers/thunderbolt/tunnel.c | 59 +++++++++++++++++++++++++++++---------------
>  4 files changed, 51 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/thunderbolt/nhi.h b/drivers/thunderbolt/nhi.h
> index c2d16ab6994e..afd9a11489a9 100644
> --- a/drivers/thunderbolt/nhi.h
> +++ b/drivers/thunderbolt/nhi.h
> @@ -169,6 +169,7 @@ struct tb_nhi_ops {
>  #define QUIRK_E2E					BIT(1)
>  #define QUIRK_RESET_DMA_ON_TEARDOWN			BIT(2)
>  #define QUIRK_NO_DMA_PORT				BIT(3)
> +#define QUIRK_NO_USB3_BW_ALLOC				BIT(4)

This is not NHI thing but lives inside the USB4 domain so the quirk should
end up in drivers/thunderbolt/quirks.c.

For now I think that's enough but in the future we should provide software
mechanism that takes over the hardware if present, and then get rid of the
quirk alltogether.

>  /*
>   * Minimal number of vectors when we use MSI-X. Two for control channel
> diff --git a/drivers/thunderbolt/tb.c b/drivers/thunderbolt/tb.c
> index c43cdd2c2e2e..7ab53a30fe30 100644
> --- a/drivers/thunderbolt/tb.c
> +++ b/drivers/thunderbolt/tb.c
> @@ -3044,6 +3044,14 @@ static int tb_start(struct tb *tb, bool reset)
>  	 */
>  	tb->root_switch->no_dma_port = tb->nhi->quirks & QUIRK_NO_DMA_PORT;
>  
> +	/*
> +	 * Apple Silicon host routers do not implement the USB3 bandwidth
> +	 * allocation registers: the CMR/HCA handshake is never acked and
> +	 * times out. Bandwidth for USB3 tunnels is only booked in software
> +	 * on these machines.
> +	 */
> +	tb->root_switch->no_usb3_bw_alloc = tb->nhi->quirks & QUIRK_NO_USB3_BW_ALLOC;
> +
>  	ret = tb_switch_configure(tb->root_switch);
>  	if (ret) {
>  		tb_switch_put(tb->root_switch);
> diff --git a/drivers/thunderbolt/tb.h b/drivers/thunderbolt/tb.h
> index 0977cd690d7e..530b0e6c3a11 100644
> --- a/drivers/thunderbolt/tb.h
> +++ b/drivers/thunderbolt/tb.h
> @@ -140,6 +140,8 @@ struct tb_switch_tmu {
>   * @nvm: Pointer to the NVM if the switch has one (%NULL otherwise)
>   * @no_nvm_upgrade: Prevent NVM upgrade of this switch
>   * @no_dma_port: Prevent adding the DMA port of this switch
> + * @no_usb3_bw_alloc: Host router does not implement the USB3 bandwidth
> + *		      allocation registers (ADP_USB3_CS_1..4)
>   * @safe_mode: The switch is in safe-mode
>   * @boot: Whether the switch was already authorized on boot or not
>   * @rpm: The switch supports runtime PM
> @@ -196,6 +198,7 @@ struct tb_switch {
>  	struct tb_nvm *nvm;
>  	bool no_nvm_upgrade;
>  	bool no_dma_port;
> +	bool no_usb3_bw_alloc;
>  	bool safe_mode;
>  	bool boot;
>  	bool rpm;
> diff --git a/drivers/thunderbolt/tunnel.c b/drivers/thunderbolt/tunnel.c
> index 7e8284575dff..9178120a6b66 100644
> --- a/drivers/thunderbolt/tunnel.c
> +++ b/drivers/thunderbolt/tunnel.c
> @@ -2268,24 +2268,40 @@ struct tb_tunnel *tb_tunnel_discover_usb3(struct tb *tb, struct tb_port *down,
>  	if (!tb_route(down->sw)) {
>  		int ret;
>  
> -		/*
> -		 * Read the initial bandwidth allocation for the first
> -		 * hop tunnel.
> -		 */
> -		ret = usb4_usb3_port_allocated_bandwidth(down,
> -			&tunnel->allocated_up, &tunnel->allocated_down);
> -		if (ret)
> -			goto err_deactivate;
> +		tunnel->consumed_bandwidth = tb_usb3_consumed_bandwidth;
> +
> +		if (down->sw->no_usb3_bw_alloc) {
> +			/*
> +			 * The host router does not implement the bandwidth
> +			 * allocation registers and nothing can be read back
> +			 * here. Book 90% of the maximum link rate in software
> +			 * instead.
> +			 */
> +			ret = tb_usb3_max_link_rate(tunnel->dst_port, down);
> +			if (ret < 0)
> +				goto err_deactivate;
> +
> +			tunnel->allocated_up = ret * 90 / 100;
> +			tunnel->allocated_down = tunnel->allocated_up;
> +		} else {
> +			/*
> +			 * Read the initial bandwidth allocation for the first
> +			 * hop tunnel.
> +			 */
> +			ret = usb4_usb3_port_allocated_bandwidth(down,
> +				&tunnel->allocated_up, &tunnel->allocated_down);
> +			if (ret)
> +				goto err_deactivate;
> +
> +			tunnel->pre_activate = tb_usb3_pre_activate;
> +			tunnel->release_unused_bandwidth =
> +				tb_usb3_release_unused_bandwidth;
> +			tunnel->reclaim_available_bandwidth =
> +				tb_usb3_reclaim_available_bandwidth;
> +		}
>  
>  		tb_tunnel_dbg(tunnel, "currently allocated bandwidth %d/%d Mb/s\n",
>  			      tunnel->allocated_up, tunnel->allocated_down);
> -
> -		tunnel->pre_activate = tb_usb3_pre_activate;
> -		tunnel->consumed_bandwidth = tb_usb3_consumed_bandwidth;
> -		tunnel->release_unused_bandwidth =
> -			tb_usb3_release_unused_bandwidth;
> -		tunnel->reclaim_available_bandwidth =
> -			tb_usb3_reclaim_available_bandwidth;
>  	}
>  
>  	tb_tunnel_dbg(tunnel, "discovered\n");
> @@ -2365,12 +2381,15 @@ struct tb_tunnel *tb_tunnel_alloc_usb3(struct tb *tb, struct tb_port *up,
>  		tunnel->allocated_up = min(max_rate, max_up);
>  		tunnel->allocated_down = min(max_rate, max_down);
>  
> -		tunnel->pre_activate = tb_usb3_pre_activate;
>  		tunnel->consumed_bandwidth = tb_usb3_consumed_bandwidth;
> -		tunnel->release_unused_bandwidth =
> -			tb_usb3_release_unused_bandwidth;
> -		tunnel->reclaim_available_bandwidth =
> -			tb_usb3_reclaim_available_bandwidth;
> +
> +		if (!down->sw->no_usb3_bw_alloc) {
> +			tunnel->pre_activate = tb_usb3_pre_activate;
> +			tunnel->release_unused_bandwidth =
> +				tb_usb3_release_unused_bandwidth;
> +			tunnel->reclaim_available_bandwidth =
> +				tb_usb3_reclaim_available_bandwidth;
> +		}
>  	}
>  
>  	return tunnel;
> 
> -- 
> 2.55.0
>