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 14:23:37 +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:
>>> Baolin Wang <baolin.wang@...aro.org> writes:
>>>>>>> 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.
>>>>
>>>> Yes, but 100us delay is not enough in some scenarios, like changing
>>>> function with configfs frequently, we will met problems.
>>>
>>> heh, 100us *is* enough. However we still get an IRQ because we requested
>>> for it. If you want to fix this, then you need to find a way to get rid
>>> of that 100us udelay() and add a proper wait_for_completion() to delay
>>> execution until command complete IRQ fires up.
>>
>> I haven't tested this yet, but it shows the idea (I think we might still
>> have a race with ep_queue if we're still waiting for End Transfer, but
>
> Yes, maybe we need check DWC3_EP_END_TRANSFER_PENDING flag when
> queuing one request.

Yeah, I'll add that check later. I still need to make sure we would
still try to kick any transfers that might have been queued while
waiting for End Transfer Command Complete IRQ.

>> that's easy to sort out by checking for DWC3_EP_END_TRANSFER_PENDING
>> before calling kick_transfer). Could you have a look and, perhaps, run a
>> test?
>
> Sure. I will test it and send out the result tomorrow.

Thank you

-- 
balbi

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