Re: [PATCH 2/2] usb: dwc3: Notify XHCI core of tunneled status

[Jack Pham]

On Thu, May 07, 2026 at 12:34:50PM +0200, Konrad Dybcio wrote:
> On 5/7/26 1:40 AM, Thinh Nguyen wrote:
> > On Tue, May 05, 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.
> >>
> >> Signed-off-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
> >> ---
> >>  drivers/usb/dwc3/core.c | 12 ++++++++++++
> >>  drivers/usb/dwc3/core.h | 18 ++++++++++++++++++
> >>  drivers/usb/dwc3/host.c | 12 ++++++++++++
> >>  3 files changed, 42 insertions(+)
> >>
> >> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> >> index 65213896de99..7cec4911e278 100644
> >> --- a/drivers/usb/dwc3/core.c
> >> +++ b/drivers/usb/dwc3/core.c
> >> @@ -162,6 +162,18 @@ void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode, bool ignore_susphy)
> >>  }
> >>  EXPORT_SYMBOL_GPL(dwc3_set_prtcap);
> >>  
> >> +enum usb_link_tunnel_mode dwc3_link_tunnel_mode(struct dwc3 *dwc, u8 port)
> >> +{
> >> +	/* Prior versions had no CIO support */
> >> +	if (!DWC3_VER_IS_WITHIN(DWC31, 191A, ANY))
> >> +		return USB_LINK_NATIVE;
> >> +
> >> +	if (dwc3_readl(dwc, DWC3_CIOCTRL(port)) & DWC3_CIOCTRL_CIO_EN)
> > 
> > The CIO register block only exists if DWC1_USB31_EN_CIO is set (and
> > DWC_USB31_EN_USB2_ONLY is not set). In most cases, this register block
> > will be reserved, register read of reserved block should be 0. But we
> > can't guarantee that it will always be the case.
> 
> That's inconvenient because..
> 
> [...]
> 
> > We shouldn't need to be doing this. This should be checked from the
> > xHCI driver. Check xHCI spec for PORTSC.TM and USB3 tunneling support
> > capability (section 7.11).
> 
> ..I'm seeing only caps 0/1/2 (and 10 on some but not all) advertised
> (I ran a for-loop checking offsets 0..=255)

Right.  That section in xHCI spec was only added in the 1.2b revision.
However the DWC31 IP versions that current Qualcomm USB4-capable SoCs
are using are 2.00a (and a customized version of 1.91a) which are only
compliant to xHCI 1.1 so this capability is not there, even though the
CIO register block exists.  So short of having the proper XHCI bit, this
is the next best, non-SoC specific alternative we've found that can
allow XHCI driver to identify when it is operating in tunnel mode.

Jack