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

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Message-ID: <7877d69b-b17c-d4a4-9806-3dca98fc9e26@redhat.com>
Date:   Fri, 18 Oct 2019 21:30:49 +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 20:39, John Stultz wrote:
> On Fri, Oct 18, 2019 at 1:06 AM Hans de Goede <hdegoede@...hat.com> wrote:
>> On 18-10-2019 07:55, John Stultz wrote:
>>> On Wed, Oct 16, 2019 at 12:27 AM Hans de Goede <hdegoede@...hat.com> wrote:
>>>> Look at the tcpm_set_vbus implementation in drivers/usb/typec/tcpm/fusb302.c
>>>> you need to do something similar in your Type-C controller driver and
>>>> export the GPIO as as a gpio-controlled regulator and tie the regulator to
>>>> the connector.
>>>
>>> Thanks for the suggestion, I really appreciate it! One more question
>>> though, since I'm using the tcpci_rt1711h driver, which re-uses the
>>> somewhat sparse tcpci.c implementation, would you recommend trying to
>>> add generic regulator support to the tcpci code or trying to extend
>>> the implementation somehow allow the tcpci_rt1711h driver replace just
>>> the set_vbus function?
>>
>> I have the feeling that this is more of a question for Heikki.
>>
>> My first instinct is: if you are using tcpci can't you put all
>> the hacks you need for the usb connection shared between hub
>> and type-c in your firmware ?
> 
> I appreciate the suggestion, but I'm not aware of any USB firmware for
> the board, nor do I think I have any such source.  :(

My bad, I was under the impression that tcpci was a firmware interface,
but it is not (I was confusing it with ucsi).

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.

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...

Regards,

Hans