Re: [PATCH v4 4/4] usb: dwc3: Notify XHCI core of tunneled status

[Thinh Nguyen]

On Tue, Sep 29, 2026, Konrad Dybcio wrote:
> From: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
> 
> The Thunderbolt framework relies on the USB core to create device links
> for tunneled ports, so that the USB3 controller is only kept
> runtime-resumed for the duration of the tunneling. This depends on
> first knowing whether a connection is tunneled or native.
> 
> Add the logic to handle that for DWC3 controllers.
> 
> Assisted-by: LLM
> Signed-off-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
> ---
>  drivers/usb/dwc3/core.c | 18 ++++++++++++++++++
>  drivers/usb/dwc3/core.h | 18 ++++++++++++++++++
>  drivers/usb/dwc3/host.c | 14 ++++++++++++++
>  3 files changed, 50 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index fd5c2cd36c59..4eb430f58983 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -162,6 +162,24 @@ void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode, bool ignore_susphy)
>  }
>  EXPORT_SYMBOL_GPL(dwc3_set_prtcap);
>  
> +#if IS_ENABLED(CONFIG_USB_DWC3_HOST) || IS_ENABLED(CONFIG_USB_DWC3_DUAL_ROLE)

Move this function to host.c instead of core.c, drop the guards, and
make it static.

> +enum usb_link_tunnel_mode dwc3_link_tunnel_mode(struct dwc3 *dwc, u8 port)
> +{

Maybe also add a check if (port >= dwc->num_usb3_ports) and return
USB_LINK_UNKNOWN?

> +	/* Prior versions had no CIO support */
> +	if (!DWC3_VER_IS_WITHIN(DWC31, 191A, ANY))
> +		return USB_LINK_UNKNOWN;

Regarding your cover letter question about CIO for other IPs. We can
leave that for later when we need to make an update.

> +
> +	/* Not all DWC3 instances have CIO HW, trust the platform firmware */
> +	if (!device_property_present(dwc->dev, "usb4-host-interface"))

Can we pass this as a dwc3 property from your glue driver instead,
inferred from the compatible string? (ie. add dwc->has_cio)

So we can remove the DT dependency.

> +		return USB_LINK_UNKNOWN;
> +
> +	if (dwc3_readl(dwc, DWC3_CIOCTRL(port)) & DWC3_CIOCTRL_CIO_EN)
> +		return USB_LINK_TUNNELED;
> +
> +	return USB_LINK_NATIVE;
> +}
> +#endif
> +
>  static void __dwc3_set_mode(struct work_struct *work)
>  {
>  	struct dwc3 *dwc = work_to_dwc(work);
> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
> index 608daeb7ef10..decc51cd6505 100644
> --- a/drivers/usb/dwc3/core.h
> +++ b/drivers/usb/dwc3/core.h
> @@ -179,6 +179,11 @@
>  #define DWC3_OEVTEN		0xcc0C
>  #define DWC3_OSTS		0xcc10
>  
> +/* CIO regs */
> +#define DWC3_CIO_BASE(n)	(0xcd20 + ((n) * 0x30))
> +#define DWC3_CIOCTRL(n)		(DWC3_CIO_BASE(n) + 0x00)
> +#define DWC3_CIOCTRL_CIO_EN	BIT(0)
> +
>  #define DWC3_LLUCTL(n)		(0xd024 + ((n) * 0x80))
>  
>  /* Bit fields */
> @@ -1314,6 +1319,7 @@ struct dwc3 {
>  #define DWC31_REVISION_170A	0x3137302a
>  #define DWC31_REVISION_180A	0x3138302a
>  #define DWC31_REVISION_190A	0x3139302a
> +#define DWC31_REVISION_191A	0x3139312a
>  #define DWC31_REVISION_200A	0x3230302a
>  
>  #define DWC32_REVISION_ANY	0x0
> @@ -1658,11 +1664,23 @@ static inline void dwc3_pre_run_stop(struct dwc3 *dwc, bool is_on)
>  #if IS_ENABLED(CONFIG_USB_DWC3_HOST) || IS_ENABLED(CONFIG_USB_DWC3_DUAL_ROLE)
>  int dwc3_host_init(struct dwc3 *dwc);
>  void dwc3_host_exit(struct dwc3 *dwc);
> +
> +/**
> + * dwc3_link_tunnel_mode - Check whether the link is tunneled over TBT/USB4
> + * @dwc: Pointer to DWC3 controller context
> + * @port: 0-based port index
> + *
> + * Returns: USB_LINK_TUNNELED if tunneled, USB_LINK_NATIVE if not, or
> + *          when the controller does not have USB4 capabilities.

Do we need to describe the USB_LINK_UNKNOWN case?

Thanks,
Thinh