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

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Message-ID: <8760uripx8.fsf@intel.com>
Date:	Fri, 06 May 2016 10:52:35 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	Peter Chen <hzpeterchen@...il.com>
Cc:	"Du\, Changbin" <changbin.du@...el.com>,
	"gregkh\@linuxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-usb\@vger.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: usb/dwc3: fake dissconnect event when turn off pullup


Hi,

Peter Chen <hzpeterchen@...il.com> writes:
>> Peter Chen <hzpeterchen@...il.com> writes:
>> >> "Du, Changbin" <changbin.du@...el.com> 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.
>> >> 
>> >
>> > If it is a gadget driver, it can call its disconnect explicitly.
>> > Another thing is the gadget driver should not call usb_gadget_disconnect
>> > directly, it should call usb_gadget_deactivate or usb_function_deactivate.
>> >
>> > Since currently, calling usb_gadget_disconnect may not do real pull down
>> > dp, Felipe, will you consider adding gadget_driver->disconnect into
>> > usb_gadget_disconnect after pull down dp?
>> 
>> this is the detail that I'm not yet entirely sure is always valid. Would
>> there ever be a situation where we want to drop pull-ups but not tell
>> the gadget about it ?
>
> Yes, we have.
>
> - We have enabled pullup dp default for most of platforms, and for
> gadget obex and uvc will pull down it since it wants app to
> control it
>
> - Some USB charger detection design may need it for the secondary
> detection.
>
> After checking again for usb_gadget_disconnect and
> usb_gadget_disconnect, I think there is no possible that the dp is
> still pulled after we call usb_gadget_disconnect, so we don't need
> to change anything:)

alright, cool. So we'll keep the requirement to call
gadget_driver->disconnect() for anybody who calls
usb_gadget_disconnect(). Caller should know if we need to notify
gadget_driver or not about that disconnect.

-- 
balbi

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