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

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Date:   Mon, 5 Mar 2018 13:14:26 +0200
From:   Roger Quadros <rogerq@...com>
To:     Felipe Balbi <balbi@...nel.org>,
        Baolin Wang <baolin.wang@...aro.org>
CC:     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

On 05/03/18 13:06, Felipe Balbi wrote:
> 
> Hi,
> 
> Baolin Wang <baolin.wang@...aro.org> writes:
>>>> 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.
> 
> We could mask command complete events as soon as ->udc_stop() is called,
> right? Hmm, actually, __dwc3_gadget_stop() already clears DEVTEN
> completely.

But which bit in DEVTEN says Endpoint events are disabled?

> 
> /me goes check databook
> 
> At least on revision 2.60a of the databook, bit 10 is reserved. I wonder
> if that's the start of all the problems. Anybody has access to older and
> newer databook revisions so we can cross-check?
> 

I can access v2.40 and v3.10 books.

bit 10 is reserved on both

Differences in v2.4 vs v3.10 are:

bit 8	reserved	vs	L1SUSPEN
bit 13	reserved	vs	StopOnDisconnectEn
bit 14	reserved	vs	L1WKUPEVTEN

-- 
cheers,
-roger

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