linux-kernel - Re: [PATCH v2] usb: dwc3: gadget: Wait for end transfer complete before free irq

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Date:   Thu, 13 Oct 2016 10:51:59 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Mark Brown <broonie@...nel.org>,
        USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: dwc3: gadget: Wait for end transfer complete before free irq


Hi,

Baolin Wang <baolin.wang@...aro.org> writes:
> Hi,
>
> On 13 October 2016 at 15:02, Felipe Balbi <balbi@...nel.org> wrote:
>>
>> Hi,
>>
>> Baolin Wang <baolin.wang@...aro.org> writes:
>>> @@ -1742,6 +1791,17 @@ static int dwc3_gadget_stop(struct usb_gadget *g)
>>>       dwc->gadget_driver      = NULL;
>>>       spin_unlock_irqrestore(&dwc->lock, flags);
>>>
>>> +     /*
>>> +      * Since the xHCI will share the same interrupt with gadget, thus when
>>> +      * free the gadget irq, it will not shutdown this gadget irq line. Then
>>> +      * the gadget driver can not handle the end transfer command complete
>>> +      * event after free the gadget irq, which will hang the system to crash.
>>> +      *
>>> +      * So we should wait for the end transfer command complete event before
>>> +      * free it to avoid this situation.
>>> +      */
>>> +     dwc3_wait_command_complete(dwc);
>>
>> this doesn't make sense. We have already masked all interrupts before
>> getting here. We have also, already, disabled all endpoints.
>
> No, you just mask the interrupts described in DEVTEN register, and you
> did not disable the endpoint command complete event.

True that

>> I'm thinking this is a bug in configfs interface of Gadget API, not
>> dwc3. The only reason for this to happen would be if we get to
>> ->udc_stop() with endpoints still enabled.
>>
>> Can you check if that's the case? i.e. can you check if any endpoints
>> are still enabled when we get here?
>
> No, it is not any endpoints are still enabled. Like I said in commit
> message, we will start end transfer command when disable the endpoint,
> if the end transfer command complete event comes after we have freed
> the gadget irq, it will trigger the interrupt line all the time to
> crash the system.

I see what the problem is. Databook tells us we *must* set CMDIOC when
issuing EndTransfer command and we should always wait for Command
Complete IRQ. However, we took a shortcut and just delayed for 100us
after issuing End Transfer.

It seems as if *that* should be fixed. We should start actually waiting
for Command Complete IRQ.

-- 
balbi

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