Re: [PATCH v5 3/4] usb: host: xhci-plat: Create platform device for onboard hubs in probe()

From: Rob Herring <robh+dt@kernel.org>
To: Stephen Boyd <swboyd@chromium.org>
Cc: Krzysztof Kozlowski <krzk@kernel.org>,
	Matthias Kaehlcke <mka@chromium.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>
Subject: Re: [PATCH v5 3/4] usb: host: xhci-plat: Create platform device for onboard hubs in probe()
Date: Thu, 11 Feb 2021 16:40:19 -0600	[thread overview]
Message-ID: <CAL_Jsq+A5YpF9ySzmL+G1g=ca4926vpPOpA71hB37p+FZ-=tWQ@mail.gmail.com> (raw)
In-Reply-To: <161307087919.1254594.11784819060723374369@swboyd.mtv.corp.google.com>

On Thu, Feb 11, 2021 at 1:14 PM Stephen Boyd <swboyd@chromium.org> wrote:
>
> Quoting Matthias Kaehlcke (2021-02-10 14:20:18)
> >
> > On Wed, Feb 10, 2021 at 10:06:45PM +0100, Krzysztof Kozlowski wrote:
> > >
> > > This looks hackish... what if later we have something else than hub?
> > > Another if()?
> > >
> > > What if hub could be connected to something else than XHCI controller?
> >
> > In earlier versions this was standalone driver, which was more flexible and
> > didn't require cooperation from the XHCI driver:
> >
> > https://lore.kernel.org/patchwork/patch/1313001/
> >
> > Rob Herring raised objections about the DT bindings, since the USB hub would 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:
> >
> > https://lore.kernel.org/patchwork/patch/1305395/
> > https://lore.kernel.org/patchwork/patch/1313000/
> >
> > Alan Stern suggested to create the platform device in the XHCI platform driver:
> >
> > https://lore.kernel.org/patchwork/patch/1313000/#1510227
> >
> > 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 driver.
> >
> > If you have better suggestions that might satisfy all parties please let us
> > know :)
> >
>
> 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.

An orphan at the root node is exactly what I don't want to see here.
I'm happy with the binding now from a skim of it. The kernel support
does seem kind of hacky though.

Rob