Re: [PATCH v2 2/4] usb: xhci: Honor PORTSC.TM if valid

[Konrad Dybcio]

On 7/23/26 12:57 AM, Thinh Nguyen wrote:
> On Wed, Jul 15, 2026, Konrad Dybcio wrote:
>> From: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
>>
>> Currently, the only way for the USB core to determine whether the link
>> is native or tunneled is via an Intel vendor-specific Extended
>> Capability.

[...]

>> -	/* Don't try and probe this capability for non-Intel hosts */
>> +	/* Prefer the XHCI v1.2 ext_cap if advertised */
>> +	offset = xhci_find_next_ext_cap(base, 0, XHCI_EXT_CAPS_USB3_TUNNELING);
>> +	if (offset) {
>> +		if (!(readl(base + offset) & XHCI_USB3_TUNNELING_SUPPORTED))
>> +			return USB_LINK_NATIVE;
> 
> Second, don't return early here. Check if XHCI_EXT_CAPS_USB3_TUNNELING
> present and supported:

So if the extcap is supported and exposed, but it says "this port
is not tunneling-capable", can we not trust that data?
> 
> 	if (offset && (readl(base + offset) & XHCI_USB3_TUNNELING_SUPPORTED)) {
> 
>> +
>> +		val = xhci_portsc_readl(port);
>> +		if (val & PORT_TM)
>> +			return USB_LINK_TUNNELED;
>> +
>> +		return USB_LINK_NATIVE;
>> +	}

Your proposed change says "if !USB3_TUNNELING_SUPPORTED, assume it may
still be supported via the Intel ext_cap below"

Konrad