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References: <20210210171040.684659-1-mka@chromium.org> <20210210091015.v5.3.I7a3a7d9d2126c34079b1cab87aa0b2ec3030f9b7@changeid> <20210210210645.xapaua7djdsvr3ca@kozik-lap> <YCRcIuCxB8nYi7/e@google.com>
Subject: Re: [PATCH v5 3/4] usb: host: xhci-plat: Create platform device for onboard hubs in probe()
From:   Stephen Boyd <swboyd@chromium.org>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rob Herring <robh+dt@kernel.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,
        Douglas Anderson <dianders@chromium.org>,
        linux-usb@vger.kernel.org, Mathias Nyman <mathias.nyman@intel.com>
To:     Krzysztof Kozlowski <krzk@kernel.org>,
        Matthias Kaehlcke <mka@chromium.org>
Date:   Thu, 11 Feb 2021 11:14:39 -0800
Message-ID: <161307087919.1254594.11784819060723374369@swboyd.mtv.corp.google.com>
User-Agent: alot/0.9.1
Precedence: bulk

Quoting Matthias Kaehlcke (2021-02-10 14:20:18)
>=20
> On Wed, Feb 10, 2021 at 10:06:45PM +0100, Krzysztof Kozlowski wrote:
> >=20
> > This looks hackish... what if later we have something else than hub?
> > Another if()?
> >=20
> > What if hub could be connected to something else than XHCI controller?
>=20
> In earlier versions this was standalone driver, which was more flexible a=
nd
> didn't require cooperation from the XHCI driver:
>=20
> https://lore.kernel.org/patchwork/patch/1313001/
>=20
> Rob Herring raised objections about the DT bindings, since the USB hub wo=
uld be
> represented twice in the DT, once in the USB hierachry (with an explicit =
node or
> implicitly) plus a node for the platform device for the new driver:
>=20
> https://lore.kernel.org/patchwork/patch/1305395/
> https://lore.kernel.org/patchwork/patch/1313000/
>=20
> Alan Stern suggested to create the platform device in the XHCI platform d=
river:
>=20
> https://lore.kernel.org/patchwork/patch/1313000/#1510227
>=20
> I wasn't super happy about involving xhci-plat, but at least the code is =
minimal
> and all the device specific stuff is handled by the onboard_usb_hub drive=
r.
>=20
> If you have better suggestions that might satisfy all parties please let =
us
> know :)
>=20

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 node
at the root of DT connected to the USB controller (or phy) and xhci code
could probe the firmware to see if there's a graph connection downstream
that is a powered hub like this. I didn't see this idea mentioned in the
previous discussions, but maybe I missed it.