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From:   Rob Herring <robh+dt@kernel.org>
Date:   Thu, 11 Feb 2021 16:46:56 -0600
Message-ID: <CAL_JsqJR5DUiDJ-fkrGbM0M2Lm5S4xQH2dhV9oi9UMhBuiVVrA@mail.gmail.com>
Subject: Re: [PATCH v5 3/4] usb: host: xhci-plat: Create platform device for
 onboard hubs in probe()
To:     Stephen Boyd <swboyd@chromium.org>
Cc:     Matthias Kaehlcke <mka@chromium.org>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Frank Rowand <frowand.list@gmail.com>,
        devicetree@vger.kernel.org, Peter Chen <peter.chen@nxp.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Ravi Chandra Sadineni <ravisadineni@chromium.org>,
        Bastien Nocera <hadess@hadess.net>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Douglas Anderson <dianders@chromium.org>,
        Linux USB List <linux-usb@vger.kernel.org>,
        Mathias Nyman <mathias.nyman@intel.com>
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On Thu, Feb 11, 2021 at 2:45 PM Stephen Boyd <swboyd@chromium.org> wrote:
>
> Quoting Matthias Kaehlcke (2021-02-11 12:36:35)
> > Hi Stephen,
> >
> > On Thu, Feb 11, 2021 at 11:14:39AM -0800, Stephen Boyd wrote:
> > >
> > > Is it possible to use the graph binding to connect the USB controller=
 on
> > > the SoC to the port on the hub? Then the hub would be a standalone no=
de
> > > at the root of DT connected to the USB controller (or phy) and xhci c=
ode
> > > could probe the firmware to see if there's a graph connection downstr=
eam
> > > that is a powered hub like this. I didn't see this idea mentioned in =
the
> > > previous discussions, but maybe I missed it.
> >
> > Thanks for bringing this up. I'm not sure I completely understand your
> > suggestion, but in general it seems a direction that could be worth
> > exploring.
>
> Cool.
>
> >
> > I think something like the following should work even without requiring
> > cooperation from the XHCI code:
> >
> > onboard-usb-hub {
> >     compatible =3D =E2=80=9Crealtek,rts5411=E2=80=9D, =E2=80=9Conboard_=
usb_hub=E2=80=9D;
> >     #address-cells =3D <1>;
> >     #size-cells =3D <0>;
> >
> >     vdd-supply =3D <&pp3300_hub>;
> >
> >     port@0 {
> >         reg =3D <0>;
> >
> >         rts5411_3_0: endpoint {
> >             // should not be needed
> >             remote-endpoint =3D <&usb_1_dwc3_port1>;
> >         };
> >     };
> >
> >     port@1 {
> >         reg =3D <1>;
> >
> >         rts5411_2_0: endpoint {
> >             // should not be needed
> >             remote-endpoint =3D <&usb_1_dwc3_port2>;
> >         };
> >     };
> > };
> >
> > &usb_1_dwc3 {
> >     dr_mode =3D "host";
> >     #address-cells =3D <1>;
> >     #size-cells =3D <0>;
> >
> >     port@1 {
> >         reg =3D <1>;
> >
> >         usb_1_dwc3_port1: endpoint {
> >             remote-endpoint =3D <&rts5411_3_0>;
> >         };
> >     };
> >
> >     port@2 {
> >         reg =3D <2>;
> >
> >         usb_1_dwc3_port2: endpoint {
> >             remote-endpoint =3D <&rts5411_2_0>;
> >         };
> >     };
> > };
> >
> > That looks like an actual description of the hardware, without multiple=
 DT
> > nodes for the hub.
> >
> > The USB part of the onboard_hub driver could determine the platform dev=
ice
> > from the remote endpoint and register the USB device with it.
>
> Yeah you got it, this is what I'm suggesting. I'd like to go even
> further and also describe the ports on "the other side" or "downstream
> facing side" of the USB hub that go to things like type-c ports or
> type-a ports. This would allow us to describe the USB topology and how
> it is physically connected to ports on the device that humans see. But
> that's mostly a job for the type-c subsystem, so it's a parallel
> discussion that's only related because of the graph binding.

I'd like to see a complete case that includes connectors. I really
need someone to worry about USB bindings with a view on the big
picture. The piecemeal additions don't result in the best design.

Rob