[RFC usb-next v5 1/3] dt-bindings: usb: add the documentation for USB root-hub

Martin Blumenstingl martin.blumenstingl at googlemail.com
Thu Oct 12 14:35:46 PDT 2017

Hi Alan,

On Thu, Oct 12, 2017 at 11:17 PM, Alan Stern <stern at rowland.harvard.edu> wrote:
> On Thu, 12 Oct 2017, Martin Blumenstingl wrote:
>> I haven't tested the described use-case. however, this patch is not
>> supposed to change the binding for actual devices.
>> USB device numbering starts at 1, while 0 is reserved for the root-hub
>> (at least from what I know).
> Actually 1 is reserved for the root hub.  External devices are numbered
> starting from 2.  (We can't use 0 for the root hub because, as you
> said, USB device numbering starts at 1!)
I just had a look at lsusb again:
$ lsusb -t
/:  Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/2p, 5000M

however, for the devicetree bindings the devices are supposed to use 1-31: [0]

Alan: just to make sure I understood you correctly: do you agree with
this patch?

> Alan Stern
>> before this patch there was no way to
>> describe the root-hub via .dts. this however is required for some
>> platforms that need to set up a PHY for each port on the root-hub
>> (Amlogic Meson GXL platform is one example: there are two ports
>> enabled on dwc3's root-hub with 2x USB2 and 1x USB3 PHYs) - so this
>> patch uses a similar binding as we already have (to describe the
>> devices) to describe the root-hub
>> Regards,
>> Martin
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[0] http://elixir.free-electrons.com/linux/v4.14-rc4/source/Documentation/devicetree/bindings/usb/usb-device.txt

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