Re: [PATCH 2/2] dt-bindings: usb: snps,dwc3: Fix downstream port numbering

[Chen-Yu Tsai]

On Wed, Oct 21, 2026 at 5:44 PM Konrad Dybcio
<konrad.dybcio@xxxxxxxxxxxxxxxx> wrote:
>
> On 10/15/26 11:00 AM, Chen-Yu Tsai wrote:
> > (Cc-ed Mathias, the xHCI driver maintainer in case I misunderstood xHCI.)
> >
> > On Thu, Oct 15, 2026 at 4:44 PM Neil Armstrong
> > <neil.armstrong@xxxxxxxxxx> wrote:
> >>
> >> On 10/14/26 18:36, Konrad Dybcio wrote:
> >>> On 10/14/26 11:44 AM, Neil Armstrong wrote:
> >>>> On 10/14/26 11:29, Chen-Yu Tsai wrote:
> >>>>> On Wed, Oct 14, 2026 at 5:28 PM Neil Armstrong
> >>>>> <neil.armstrong@xxxxxxxxxx> wrote:
>
> [...]
>
>
> >> How about the USB4, does it use the USB3.0 port ?
> >
> > I'm not familiar with USB4. A quick search says that it can tunnel
> > USB 3.x, DP, and PCIe, and it doesn't have its own USB HCI defined.
> >
> > So I'm thinking the USB4 controller would be more like a nexus node
> > or multiplexing node, or perhaps like a USB C connector. It has input
> > ports for all the protocols it can tunnel, connected to their respective
> > controllers (XHCI, DP, PCIe). The binding probably would be very messy
> > if one controller supported multiple outgoing ports, as each downstream
> > port has a 3-to-1 relationship with its respective upstream protocol
> > interfaces.
>
> Yeah that is more or less it.
>
> There needs to be a connection between the USB4 router and the native
> (USB3 *port*, not hub | PCIe *port*, not RC | DPTX) protocol adapter
> where the tunneled packets end up at to create a PM devlink between it
> and the USB4 router.
>
> ACPI does that by adding a `usb4-host-interface = &reference_to_router`
> property, for DT that's still undecided:
>
> https://github.com/devicetree-org/dt-schema/pull/196
>
> As far as the Qualcomm implementation goes, I was hoping we could
> go forward with base1 numbering as the DWC3 is an XHCI controller:
>
> https://lore.kernel.org/linux-usb/20260929-topic-dwc3_tunneling_state-v4-0-63e296346d57@xxxxxxxxxxxxxxxx/

I don't have DWC3 manuals, but assuming its internal numbering follows
that of XHCI, you can't just use "udev->portnum - 1" in patch 4. That
is the logical port number on the root hub.

Instead you need

    raw_port = usb_hcd_find_raw_port_number(bus_to_hcd(hub->bus), port1);

to get the 1-based port number for XHCI.


ChenYu