Re: [PATCH 1/2] usb: host: xhci: Allow non-Intel usb_link_tunnel_mode reporting

[Mathias Nyman]

On 5/7/26 13:40, Konrad Dybcio wrote:
> On 5/5/26 2:14 PM, Mika Westerberg wrote:
> > Hi,
> >
> > On Tue, May 05, 2026 at 10:55:04AM +0200, 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.
> > >
> > > Currently, retrieving that information is only possibe on Intel XHCI
> > > hosts, through a vendor-specific capability. Extend xhci-plat to allow
> > > plumbing a custom one.
> > >
> > > Signed-off-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
> > > ---
> > >   drivers/usb/host/xhci-hub.c  | 4 ++--
> > >   drivers/usb/host/xhci-plat.c | 2 ++
> > >   drivers/usb/host/xhci-plat.h | 1 +
> > >   drivers/usb/host/xhci.c      | 6 +++++-
> > >   drivers/usb/host/xhci.h      | 5 ++++-
> > >   5 files changed, 14 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
> > > index bacd0ddd0d09..09e5da912066 100644
> > > --- a/drivers/usb/host/xhci-hub.c
> > > +++ b/drivers/usb/host/xhci-hub.c
> > > @@ -750,7 +750,7 @@ static int xhci_exit_test_mode(struct xhci_hcd *xhci)
> > >   }
> > >   
> > >   /**
> > > - * xhci_port_is_tunneled() - Check if USB3 connection is tunneled over USB4
> > > + * xhci_port_tunnel_mode() - Check if USB3 connection is tunneled over USB4
> > >    * @xhci: xhci host controller
> > >    * @port: USB3 port to be checked.
> > >    *
> > > @@ -764,7 +764,7 @@ static int xhci_exit_test_mode(struct xhci_hcd *xhci)
> > >    * detecting USB3 over USB4 tunnels. USB_LINK_NATIVE or USB_LINK_TUNNELED
> > >    * otherwise.
> > >    */
> > > -enum usb_link_tunnel_mode xhci_port_is_tunneled(struct xhci_hcd *xhci,
> > > +enum usb_link_tunnel_mode xhci_port_tunnel_mode(struct xhci_hcd *xhci,
> > >   						struct xhci_port *port)
> >
> > I'm wondering if this could be:
> >
> > bool xhci_port_is_tunneled()
> >
> > becase if I understand correctly that's the only information we need e.g is
> > it going over tunnel or not.
>
> It was originally introduced as a tristate enum in:
>
> f46a6e165197 ("usb: Add tunnel_mode parameter to usb device structure")
>
> but the usefulness of USB_LINK_UNKNOWN is limited to a dev_dbg() print..
> I don't really have strong opinions either way

Tunnel detection can be tried other ways if state is USB_LINK_UNKNOWN.

For example usb-acpi.c will try to create a tunnel if all the ACPI entries exists
that indicate a tunnel, but the current xHC doesn't support tunnel detection.

usb_acpi_find_companion_for_device(struct usb_device *udev)
{
	...

	/* Tunneled USB3 devices depend on USB4 Host Interface, set device link to it */
	if (udev->speed >= USB_SPEED_SUPER &&
		udev->tunnel_mode != USB_LINK_NATIVE)
		usb_acpi_add_usb4_devlink(udev);
}

-Mathias