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

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 5/7/26 1:40 AM, Thinh Nguyen wrote:
> On Tue, May 05, 2026, 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. 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@oss.qualcomm.com>
>> ---
>>  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)

How should we proceed?

Konrad