linux-kernel - Re: [PATCH v16 6/7] usb: host: xhci-plat: Create platform device for onboard hubs in probe()

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Message-ID: <YXCDobJSuytwthoA@google.com>
Date:   Wed, 20 Oct 2021 14:01:21 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Felipe Balbi <balbi@...nel.org>, devicetree@...r.kernel.org,
        Peter Chen <peter.chen@...nel.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Bastien Nocera <hadess@...ess.net>,
        Ravi Chandra Sadineni <ravisadineni@...omium.org>,
        Michal Simek <michal.simek@...inx.com>,
        Douglas Anderson <dianders@...omium.org>,
        Roger Quadros <rogerq@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Dmitry Osipenko <digetx@...il.com>,
        Fabio Estevam <festevam@...il.com>
Subject: Re: [PATCH v16 6/7] usb: host: xhci-plat: Create platform device for
 onboard hubs in probe()

On Wed, Oct 20, 2021 at 04:37:20PM -0400, Alan Stern wrote:
> On Wed, Oct 20, 2021 at 01:27:40PM -0700, Matthias Kaehlcke wrote:
> > Hi Mathias,
> > 
> > On Wed, Oct 20, 2021 at 04:05:37PM +0300, Mathias Nyman wrote:
> > > If separate devices for controlling onboard hub power is the right solution then
> > > how about creating the onboard hub device in usb_add_hcd() (hcd.c), and
> > > store it in struct usb_hcd.
> > > 
> > > A bit like how the roothub device is created, or PHYs are tuned.
> > 
> > Sure, that sounds feasible, even better if it's handled in a single place
> > and different types of controllers don't have to add support separately.
> 
> Bear in mind that this would prevent you from working with onboard
> non-root hubs.

My goal is to (architecturally) support nested hubs, but TBH I haven't
looked much into such a configuration since I don't have hardware for
testing. My assumption was that support for onboard hubs connected to
non-root hubs whould have to be added to the generic hub driver.

Could you elaborate in how far you think it would be different for
xhci_plat vs generic hcd?