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

[Mathias Nyman <mathias.nyman@linux.intel.com>]

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@oss.qualcomm.com>
>>>
>>> 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@oss.qualcomm.com>
>>> ---
>>>   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