Re: [PATCH] usb: musb: fix idling for suspend after disconnect interrupt

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On Thu, Dec 12, 2019 at 08:09:46AM -0800, Tony Lindgren wrote:
> Hi,
> 
> * Bin Liu <b-liu@xxxxxx> [191212 16:02]:
> > Hi Tony,
> > 
> > Sorry for my late response.
> 
> No worries.
> 
> > On Mon, Nov 25, 2019 at 07:41:51PM -0800, Tony Lindgren wrote:
> > > When disconnected as USB B-device, we sometimes get a suspend interrupt
> > > after disconnect interrupt. In that case we have devctl set to 99 with
> > > VBUS still valid and musb_pm_runtime_check_session() wrongly things we
> > > have an active session. We have no other interrupts after disconnect
> > > coming in this case at least with the omap2430 glue.
> > 
> > I don't have an omap2430 platform to test, but its musb doesn't generate
> > DISCONNECT interrupt at all when disconnected from USB host in any case?
> > It is a surprise, the musb core driver expects the DISCONNECT interrupt
> > after VBUS is lost and relies on it to tear down the gadget driver and
> > the state machine. I am wondering how its USB is functional without the
> > DISCONNECT event...
> 
> We do get DISCONNECT, but we can then get a SUSPEND after DISCONNECT
> has already happened..

Ahh, I missed the first sentence in the commit log...
Now I understand the issue. Thanks.

> 
> That will wake up musb waiting for further interrupts thinking it's
> connected. But after that there are no more interrupts as the cable
> is disconnected so we need to poll the status again.
> 
> If we see SUSPEND before DISCONNECT, then things idle fine.

Does SUSPEND always comes after DISCONNECT on omap2430, or just
sometimes? I guess the USB connector has some issue - when DP/DM pins
are disconnected, SUSPEND interrupt is generated; when VBUS/GND pins are
disconnected, DISCONNECT interrupt is generated. Because DP/DM pins are
shorter than VBUS/GND, SUSPEND should come before DISCONNECT.

-Bin.



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