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

From: Felipe Balbi
Date: Thu Oct 13 2016 - 09:34:57 EST


Baolin Wang <> writes:
>> Baolin Wang <> writes:
>>>>> Baolin Wang <> 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.
> OK. But I still worried if there are other races in some places which

There are no other places where this needs to be sorted out.

> is not easy to find out by testing. No introducing race condition
> would be one better solution, anyway I would like to test the patch
> you send out firstly.

Right, but your patch was working around another problem, rather then
fixing it.

Here's another version which should make sure everything remains working
as it should.