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

Alan Stern stern at rowland.harvard.edu
Thu Oct 12 14:17:01 PDT 2017

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!)

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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