Re: [PATCH v6 06/16] usb: hub: Associate port@ fwnode with USB port device

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

On 9/4/26 12:30 PM, Chen-Yu Tsai wrote:
> (dug this out of my kernel.org email)
> 
> On Fri, Jul 31, 2026 at 10:44 PM Konrad Dybcio
> <konrad.dybcio@oss.qualcomm.com> wrote:
>>
>> On 7/21/26 8:54 AM, Chen-Yu Tsai wrote:
>>> When a USB hub port is connected to a connector in a firmware node
>>> graph, the port itself has a node in the graph.

[...]

>> But something I faced when I was poking at USB4 was that dt-bindings
>> currently assume every controller is effectively single-port and the
>> of_graph ports under it represent HS/SS lanes, i.e. the entire
>> "ports" subnode represents a single USB port
> 
> Which controller is this? AFAIK for xHCI hosts there currently is no
> "ports" node specified in the common usb-hcd.yaml binding. I plan to
> add this separately, as it can already be used for USB A connectors.

DWC3, the qcom flavor specifically (qcom,snps-dwc3)

> The kernel maps every downstream port of the root hub to a separate
> node. On the XHCI it is more complicated because it has two root hubs,
> one for HS and one for SS. I'm not familiar with the hardware specifics
> but they seem to map into one common namespace, so you probably get
> ports 1~8 for HS and then 9~12 for SS. Note the number of ports is
> different. This is just an example from my x86 workstation. And on
> x86 each port is mapped to a different ACPI node.
> 
>> I think the solution here would be to do ports {} under the controller
>> and have every one of them have 2 endpoints (for HS and SS
>> respectively) - then, each DT-port would correspond to a USB port
>> (sorta like in the hub case, minus the hubs are split for HS/SS so
>> they have just a single endpoint under each port)
> 
> But the hardware descriptors actually give two ports, one for HS and one
> for SS. And in the case of dwc3, I suspect that they always come with
> one downstream HS port and (optionally) one downstream SS port. So the
> binding is actually correct, except for the numbering.

Ohh yeah I overlooked the HS/SS port split.. I think you're right!

> I'm looking into the dwc3 case. Changing the numbering might actually
> not break anything. Linux seems to just need one *a* graph connection,
> but doesn't care about the number. I looked through some other projects:
> 
> - FreeBSD doesn't use the OF graph for anything
> - U-boot doesn't use the OF graph for USB
> - OpenBSD doesn't support dwc3, only the XHCI in dwc3, and doesn't use the
>   OF graph for USB
> - coreboot doesn't use the OF graph for anything
> - Zephyr doesn't support dwc3
> - TF-A doesn't use the OF graph for anything
> - EDK2 doesn't support dwc3 and doesn't support OF graph
> - OP-TEE doesn't support dwc3 and doesn't support OF graph
> 
>> But that comes with a big breakage, as always..
> 
> As I mentioned, it probably isn't as large of a breakage.

That's very welcome for a change! Thanks for checking all of them.

Konrad