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

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Message-ID: <94cd6377-1327-2309-8d69-6ab0de2bdfd4@ti.com>
Date:   Wed, 28 Feb 2018 11:59:14 +0200
From:   Roger Quadros <rogerq@...com>
To:     Felipe Balbi <balbi@...nel.org>
CC:     <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: Prevent indefinite sleep in _dwc3_set_mode
 during suspend/resume

Felipe,

On 28/02/18 09:53, Felipe Balbi wrote:
> 
> Hi,
> 
> 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.

-- 
cheers,
-roger

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