linux-kernel - Re: [PATCH] usb: dwc3: Prevent indefinite sleep in _dwc3_set

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Date:   Mon, 5 Mar 2018 18:41:30 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Roger Quadros <rogerq@...com>
Cc:     Felipe Balbi <balbi@...nel.org>, USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: Prevent indefinite sleep in _dwc3_set_mode
 during suspend/resume

Hi Roger,

On 5 March 2018 at 17:45, Roger Quadros <rogerq@...com> wrote:
> Felipe,
>
> On 05/03/18 10:49, Felipe Balbi wrote:
>>
>> Hi,
>>
>> Roger Quadros <rogerq@...com> writes:
>>>> Roger Quadros <rogerq@...com> writes:
>>>>> In the following test we get stuck by sleeping forever in _dwc3_set_mode()
>>>>> after which dual-role switching doesn't work.
>>>>>
>>>>> On dra7-evm's dual-role port,
>>>>> - Load g_zero gadget driver and enumerate to host
>>>>> - suspend to mem
>>>>> - disconnect USB cable to host and connect otg cable with Pen drive in it.
>>>>> - resume system
>>>>> - we sleep indefinitely in _dwc3_set_mode due to.
>>>>>   dwc3_gadget_exit()->usb_del_gadget_udc()->udc_stop()->
>>>>>    dwc3_gadget_stop()->wait_event_lock_irq()
>>>>>
>>>>> Let's clear the DWC3_EP_END_TRANSFER_PENDING flag on all endpoints
>>>>> so we don't wait in dwc3_gadget_stop().
>>>>>
>>>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>>>> ---
>>>>>  drivers/usb/dwc3/gadget.c | 14 ++++++++++++++
>>>>>  1 file changed, 14 insertions(+)
>>>>>
>>>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>>>> index 2bda4eb..0a360da 100644
>>>>> --- a/drivers/usb/dwc3/gadget.c
>>>>> +++ b/drivers/usb/dwc3/gadget.c
>>>>> @@ -3273,6 +3273,20 @@ int dwc3_gadget_init(struct dwc3 *dwc)
>>>>>
>>>>>  void dwc3_gadget_exit(struct dwc3 *dwc)
>>>>>  {
>>>>> +  int epnum;
>>>>> +  unsigned long flags;
>>>>> +
>>>>> +  spin_lock_irqsave(&dwc->lock, flags);
>>>>> +  for (epnum = 2; epnum < DWC3_ENDPOINTS_NUM; epnum++) {
>>>>> +          struct dwc3_ep  *dep = dwc->eps[epnum];
>>>>> +
>>>>> +          if (!dep)
>>>>> +                  continue;
>>>>> +
>>>>> +          dep->flags &= ~DWC3_EP_END_TRANSFER_PENDING;
>>>>> +  }
>>>>> +  spin_unlock_irqrestore(&dwc->lock, flags);
>>>>> +
>>>>>    usb_del_gadget_udc(&dwc->gadget);
>>>>>    dwc3_gadget_free_endpoints(dwc);
>>>>
>>>> free endpoints is a better place for this. It's already going to free
>>>> the memory anyway. Might as well clear all flags to 0 there.
>>>>
>>>
>>> But it won't solve the deadlock issue. Since dwc3_gadget_free_endpoints()
>>> is called after usb_del_gadget_udc() and the deadlock happens when
>>>
>>> usb_del_gadget_udc()->udc_stop()->dwc3_gadget_stop()->wait_event_lock_irq()
>>>
>>> and DWC3_EP_END_TRANSFER_PENDING flag is set.
>>
>> indeed. Iterating twice over the entire endpoint list seems
>> wasteful. Perhaps we just shouldn't wait when removing the UDC since
>> that's essentially what this patch will do, right? If you clear the flag
>> before calling ->udc_stop(), this means the loop in dwc3_gadget_stop()
>> will do nothing. Might as well remove it.
>>
>
> This means that we will never wait for DWC3_EP_END_TRANSFER_PENDING to clear
> in dwc3_gadget_stop() like we used to. This is perfectly fine, right?
>
> It makes sense to me as dwc3_gadget_stop() calls __dwc3_gadget_stop() which
> masks all interrupts and nobody will ever clear that flag if it was set.

I don't think so. It can not mask the endpoint events, please check
the events which will be masked in DEVTEN register. The reason why we
should wait for DWC3_EP_END_TRANSFER_PENDING to clear is that,
sometimes the DWC3_DEPEVT_EPCMDCMPLT event will be triggered later
than 100us, but now we may have freed the gadget irq which will cause
crash.

-- 
Baolin.wang
Best Regards