linux-kernel - Re: [RFC][PATCH 2/3] usb: roles: Add usb role switch notifier.

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Date:   Fri, 18 Oct 2019 13:12:18 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     lkml <linux-kernel@...r.kernel.org>, Yu Chen <chenyu56@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Felipe Balbi <balbi@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Jun Li <lijun.kernel@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Linux USB List <linux-usb@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [RFC][PATCH 2/3] usb: roles: Add usb role switch notifier.

On Fri, Oct 18, 2019 at 12:59 PM Hans de Goede <hdegoede@...hat.com> wrote:
> On 18-10-2019 21:53, John Stultz wrote:
> > On Fri, Oct 18, 2019 at 12:30 PM Hans de Goede <hdegoede@...hat.com> wrote:
> >> Looking at drivers/usb/typec/tcpm/tcpci.c: tcpci_set_vconn I see that
> >> there is a data struct with vendor specific callbacks and that the
> >> drivers/usb/typec/tcpm/tcpci_rt1711h.c implements that.
> >>
> >> So you may want something similar here. But things are tricky here,
> >> because when nothing is connected you want to provide Vbus for
> >> the USB-A ports, which means that if someone then connects a
> >> USB-A to C cable to connect the board to a PC (switching the port
> >> to device mode) there will be a time when both sides are supplying
> >> 5V if I remember the schedule correctly.
> >
> > Ok. Thanks for the pointer, I'll take a look at that to see if I can
> > get it to work.
> >
> >> I think that the original hack might not be that bad, the whole hw
> >> design seems so, erm, broken, that you probably cannot do proper
> >> roleswapping anyways.  So just tying Vbus to host mode might be
> >> fine, the question then becomes again how can some other piece
> >> of code listen to the role-switch events...
> >
> > So, at least in the current approach (see the v3 series), I've
> > basically set the hub driver as an role-switch intermediary, sitting
> > between the calls from the tcpm to the dwc3 driver. It actually works
> > better then the earlier notifier method (which had some issues with
> > reliably establishing the initial state on boot).  Does that approach
> > work for you?
>
> That sounds like it might be a nice solution. But I have not seen the
> code, I think I was not Cc-ed on v3. Do you have a patchwork or
> lore.kernel.org link for me?

Oh! I think I had you on CC, maybe it got caught in your spam folder?
My apologies either way! The thread is here:
  https://lore.kernel.org/lkml/20191016033340.1288-1-john.stultz@linaro.org/

And the hub/role-switch-intermediary driver is here:
  https://lore.kernel.org/lkml/20191016033340.1288-12-john.stultz@linaro.org/

thanks
-john