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

[Konrad Dybcio]

On 5/7/26 2:48 PM, Mathias Nyman wrote:
> 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.

Fair, I didn't consider that!

Konrad