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

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Message-ID: <7ea7824f-abc2-4cf6-720a-3668b6286781@redhat.com>
Date:   Fri, 18 Oct 2019 21:59:51 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     John Stultz <john.stultz@...aro.org>
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.

Hi,

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?

Regards,

Hans