Re: [PATCH 0/5] usb: xhci: Fix breakage on dual-role case

[Mathias Nyman]

On 20.08.2015 10:09, Roger Quadros wrote:
> Hi Mathias,

Hi

> On 18/08/15 13:39, Roger Quadros wrote:
> > Hi,
> >
> > Plugging and unplugging a USB-OTG adapter with a USB device into a
> > am437x-gp-evm dual-role port (USB1) causes XHCI to malfunction
> > and USB device to be no longer detected after a few iterations.
> >
> > The triggering case is so
> > 1) USB1 in peripheal mode
> > 2) plug OTG adapter with USB device
> > 3) USB1 switches to host mode
> > 4) Detects new USB device
> > 5) unplug OTG adapter
> > 6) OTG core tries to remove host controller while new device
> > is being processed.
> >
> > At 6 some races are observed in the XHCI driver causing it to
> > malfunction. See kernel log at the end of this mail.
> >
> > This series tries to address some of the issues.
> > Althouth it is not 100% fool proof yet and XHCI can still get
> > stuck up for a few seconds occasionally, it did recover always
> > in a max of 10 seconds and the USB device was enumerated after
> > that.
> >
> > During a dual-role switch, usb_remove_hcd() and usb_add_hcd()
> > will be called consecutively for both Shared and Primary
> > HCDs. This can happen asynchronously and we have to be prepared
> > for it.
>
> Even after this series I do occasionally see a delay of 5 seconds
> during adapter detach. (please see kernel log below).
>
> Is it possible to further optimize so that when xhci_stop is called
> we don't depend entirely on timeout timers to stop queued commands?

Yes, sounds reasonable. Command timer and ring could probably be stopped,
remaining commands aborted and returned.
 
-Mathias
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