Re: [PATCH v3 1/4] usb: xhci: debugfs: Expose the USB3 tunneling ext_cap register value

[Thinh Nguyen]

On Tue, Sep 01, 2026, Konrad Dybcio wrote:
> From: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
> 
> The USB3 Tunneling Support Capability (idx 18) features a single
> register. Expose it over debugfs, if supported by the controller.
> 
> Signed-off-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
> ---
>  drivers/usb/host/xhci-debugfs.c  | 9 +++++++++
>  drivers/usb/host/xhci-debugfs.h  | 2 ++
>  drivers/usb/host/xhci-ext-caps.h | 1 +
>  3 files changed, 12 insertions(+)
> 
> diff --git a/drivers/usb/host/xhci-debugfs.c b/drivers/usb/host/xhci-debugfs.c
> index 2aa01d99f23d..f4bb66a9845a 100644
> --- a/drivers/usb/host/xhci-debugfs.c
> +++ b/drivers/usb/host/xhci-debugfs.c
> @@ -82,6 +82,10 @@ static const struct debugfs_reg32 xhci_extcap_dbc[] = {
>  	dump_register(EXTCAP_DBC_DEVINFO2),
>  };
>  
> +static const struct debugfs_reg32 xhci_extcap_usb3_tunneling[] = {
> +	dump_register(EXTCAP_USB3_TUNNELING),
> +};
> +
>  static struct dentry *xhci_debugfs_root;
>  
>  static struct xhci_regset *xhci_debugfs_alloc_regset(struct xhci_hcd *xhci)
> @@ -816,6 +820,11 @@ void xhci_debugfs_init(struct xhci_hcd *xhci)
>  				   ARRAY_SIZE(xhci_extcap_dbc),
>  				   "reg-ext-dbc");
>  
> +	xhci_debugfs_extcap_regset(xhci, XHCI_EXT_CAPS_USB3_TUNNELING,
> +				   xhci_extcap_usb3_tunneling,
> +				   ARRAY_SIZE(xhci_extcap_usb3_tunneling),
> +				   "reg-usb3-tunneling");
> +
>  	xhci_debugfs_create_ring_dir(xhci, &xhci->cmd_ring,
>  				     "command-ring",
>  				     xhci->debugfs_root);
> diff --git a/drivers/usb/host/xhci-debugfs.h b/drivers/usb/host/xhci-debugfs.h
> index 7c074b4be819..ca6b7f2da8e3 100644
> --- a/drivers/usb/host/xhci-debugfs.h
> +++ b/drivers/usb/host/xhci-debugfs.h
> @@ -70,6 +70,8 @@
>  #define REG_EXTCAP_DBC_DEVINFO1				0x38
>  #define REG_EXTCAP_DBC_DEVINFO2				0x3c
>  
> +#define REG_EXTCAP_USB3_TUNNELING			0x00
> +
>  #define dump_register(nm)				\
>  {							\
>  	.name	= __stringify(nm),			\
> diff --git a/drivers/usb/host/xhci-ext-caps.h b/drivers/usb/host/xhci-ext-caps.h
> index 67ecf7320c62..22e53a750e2a 100644
> --- a/drivers/usb/host/xhci-ext-caps.h
> +++ b/drivers/usb/host/xhci-ext-caps.h
> @@ -40,6 +40,7 @@
>  #define XHCI_EXT_CAPS_ROUTE	5
>  /* IDs 6-9 reserved */
>  #define XHCI_EXT_CAPS_DEBUG	10
> +#define XHCI_EXT_CAPS_USB3_TUNNELING	18
>  /* Vendor caps */
>  #define XHCI_EXT_CAPS_VENDOR_INTEL	192
>  #define XHCI_EXT_CAPS_INTEL_SPR_SHADOW	206
> 
> -- 
> 2.55.0
> 

Reviewed-by: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>

Thanks,
Thinh