[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 19 14:25:48 PDT 2017

Hi Arnd,

On Wed, Oct 18, 2017 at 11:05 AM, Arnd Bergmann <arnd at arndb.de> wrote:
> On Tue, Oct 17, 2017 at 11:19 PM, Martin Blumenstingl
> <martin.blumenstingl at googlemail.com> wrote:
>>> Ok, very good!
>>>> is there anything else you want me to test?
>>> What about the same dtb when run on a kernel without your
>>> patch series? Does that work as well, or are your patches
>>> required to make it work?
>> this is the only device I have which uses devicetree and a xHCI
>> controller. I can test it with a dwc2 based device though if you want
> Does dwc2 also use separate nodes for the roothub? From your
> description it sounds like it would not be affected by your patch.
currently it doesn't use separate notes for the roothub - however,
with this patch it could (although I haven't explicitly tested this)

> To rephrase what I'm interested in, can you check that with your
> patch series, we correctly associate a device node in DT with the
> struct device in the kernel both with and without the optional
> roothub node in the dtb?
I can do the same tests that Neil did with SoCs that use a dwc2
controller (Amlogic Meson8m2 and Meson8b).
the only SoC I have which uses a dwc3 controller is an Amlogic Meson
GXL - however this won't see any devices (apart from the root-hub)
without this patch

> Since you used a dtb that already listed an endpoint device below
> an xhci, that would answer my earlier question of whether it worked
> before your patch series, and you tested that it still works with your
> patches applied and the roothub node added in the dtb.  Now we
> just need to make sure we don't break existing dtb files that don't
> have the roothub node but do have endpoint device nodes.
the endpoint you're seeing is the root-hub - you can see the full .dts here: [0]

maybe my patch description or documentation is not clear - could you
please explain what makes you think that specifying the root-hub
didn't work before (so I can update the comments where needed)?
to sum up what this series does: find the node with reg = <0>; (= the
root-hub) and get all PHY instances from the child-nodes
this should not change any existing behavior except if someone had a
node with reg = <0>; below any USB controller node (which was
undocumented behavior before my patches)


[0] https://github.com/xdarklight/linux/blob/meson-gxl-usb-v6/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi#L55

More information about the linux-amlogic mailing list