Re: [PATCH] usb: dwc3: usb/dwc3: fake dissconnect event when turn off pullup

From: Felipe Balbi
Date: Wed May 04 2016 - 06:42:35 EST


John Youn <John.Youn@xxxxxxxxxxxx> writes:
>> John Youn <John.Youn@xxxxxxxxxxxx> writes:
>>>> "Du, Changbin" <changbin.du@xxxxxxxxx> writes:
>>>>> Hi, Balbi,
>>>>> The step to reproduce this issue is:
>>>>> 1) connect device to a host and wait its enumeration.
>>>>> 2) trigger software disconnect by calling function
>>>>> usb_gadget_disconnect(), which finally call
>>>>> dwc3_gadget_pullup(false). Do not reconnect device
>>>>> (I mean no enumeration go on, keep bit Run/Stop 0.).
>>>>> At here, gadget driver's disconnect callback should be
>>>>> Called, right? We has been disconnected. But no, as
>>>>> You said " not generating disconnect IRQ after you
>>>>> drop Run/Stop is expected".
>>>>> And I am testing on an Android device, Android only
>>>>> use dwc3_gadget_pullup(false) to issue a soft disconnection.
>>>>> This confused user that the UI still show usb as connected
>>>>> State, caused by missing a disconnect event.
>>>> okay, so I know what this is. This is caused by Android gadget itself
>>>> not notifying the gadget that a disconnect has happened. Just look at
>>>> udc-core's soft_connect implementation for the sysfs interface, and
>>>> you'll see what I mean.
>>>> This should be fixed at Android gadget itself. The only thing we could
>>>> do is introduce a new usb_gadget_soft_connect()/disconnect() to wrap the
>>>> logic so it's easier for Android gadget to use; but even that I'm a
>>>> little bit reluctant to do because Android should be using our
>>>> soft_connect interface instead of reimplementing it (wrongly) by its
>>>> own.
>>> We've run in to the same issue with our usb_gadget_driver.
>>> If the usb_gadget_disconnect() API function, which seems like it is
>>> intended to be called by the gadget_driver, does cause the gadget to
>>> disconnect, it seems reasonable to expect the gadget or the UDC core
>>> to notify the gadget_driver via the callback.
>> Well, the API is supposed to disconnect D+ pullup and that's about it.
>>> As you mentioned this is handled in the soft_disconnect sysfs. Why
>>> shouldn't usb_gadget_disconnect() do the same thing, if not the gadget
>> because there might be cases where we don't need/want the gadget to know
>> about this disconnect.
> But what if we do?

well, if the gadget is the one faking a disconnect, then it ought to
cancel requests and do all the other necessary steps, right ? :-)

>>> itself? Exposing the sysfs as an API function would work too. Though
>> it already _is_ exported. I just don't know why people are re-inventing
>> the same solution :-)
>>> both functions are "soft" disconnects and both are called
>>> "disconnect".
>>> In our gadget_driver we do the workaround where we notify ourself that
>>> we called the usb_gadget_disconnect() and that we should now be
>> you could just rely on the sysfs interface, right ? :-)
> Not from the gadget driver, at least I don't think so. The gadget
> driver itself is the one that wants to initiate the soft disconnect.

I need to understand this requirement of yours a little better. Can you
describe exactly what your gadget is doing ? Also, any chance of showing
the code for that gadget ? I don't mind carrying an extra function
driver if it helps you validate your IP :-)


Attachment: signature.asc
Description: PGP signature