linux-kernel - Re: [RFC][PATCH 1/3 v2] usb: dwc2: Add extcon support to dwc2 driver

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Date:   Tue, 6 Dec 2016 17:44:23 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     John Youn <John.Youn@...opsys.com>
Cc:     lkml <linux-kernel@...r.kernel.org>, Wei Xu <xuwei5@...ilicon.com>,
        Guodong Xu <guodong.xu@...aro.org>,
        Amit Pundir <amit.pundir@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Douglas Anderson <dianders@...omium.org>,
        Chen Yu <chenyu56@...wei.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [RFC][PATCH 1/3 v2] usb: dwc2: Add extcon support to dwc2 driver

On Tue, Dec 6, 2016 at 4:35 PM, John Stultz <john.stultz@...aro.org> wrote:
> On Tue, Dec 6, 2016 at 4:26 PM, John Youn <John.Youn@...opsys.com> wrote:
>> On 12/6/2016 4:05 PM, John Stultz wrote:
>>> On Tue, Dec 6, 2016 at 3:17 PM, John Youn <John.Youn@...opsys.com> wrote:
>>>> Also, do you really need this at all? Wasn't your system previously
>>>> able to detect the ID pin change correctly via the connection id
>>>> status change interrupt? This would only be needed if that were not
>>>> the case.
>>>
>>> So it can be made work w/o this, but we needed other hacks because the
>>> usb-gadget disconnect logic never triggered when the cable was
>>> unplugged. The controller would jump over to host mode, then when we
>>> re-plugged in the usb-gadget cable, it would fail often as we never
>>> got a disconnect signal.  That's why earlier I was using this hack to
>>> force gadget disconnect before the reset was called:
>>> https://lkml.org/lkml/2016/10/20/26
>>
>> Other than the triggering WARN_ON() in fifo init, is there any other
>> negative effects?
>
> Well, when we see the WARN_ON, it doesn't connect into usb-gadget
> mode. I had to unplug and re-plug the cable.
> (The hack I linked to above avoids this, but I suspect its not correct).
>
> Also Amit Pundir had mentioned earlier that the UDC sysfs state
> doesn't get reported correctly since it doesn't register the
> usb-gadget as unplugged until the cable is re-inserted.

Actually, this is still an outstanding issue, as
/sys/class/udc/f72c0000.usb/state seems to be stuck at "configured" no
matter the state of the cable, even with my patches. I'll need to look
further at the details there.

thanks
-john