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

From: John Youn
Date: Sun May 01 2016 - 21:47:05 EST

On 4/28/2016 11:12 PM, Felipe Balbi wrote:
> Hi,
> 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?

>> 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.

>> disconnected. It just seems more correct that we shouldn't have to
>> handle that.
>> By the way, I'm not completely sure of the correct terminology, but
>> I'm referring to the struct usb_gadget (dwc3, dwc2, etc) as the
>> "gadget" and the struct usb_gadget_driver as the "gadget_driver"
>> (normally this would be the composite gadget framework, but we are
>> using our own driver in this case). Is there a less confusing way to
>> refer to these :)
> what I've been doing is that I refer to dwc3, dwc3, etc as UDC (as in
> USB Device Controller) and g_mass_storage, g_ether, g_zero, etc as
> gadget driver.

Ok thanks, that's less confusing than calling them gadgets :)