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    SubjectRe: [PATCH v2] usb: dwc3: gadget: Wait for end transfer complete before free irq
    Hi Felipe,

    On 13 October 2016 at 19:23, Felipe Balbi <balbi@kernel.org> wrote:
    >
    > Hi,
    >
    > Baolin Wang <baolin.wang@linaro.org> writes:
    >>>> Baolin Wang <baolin.wang@linaro.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.

    OK. But I still worried if there are other races in some places which
    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.

    >
    >>> 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



    --
    Baolin.wang
    Best Regards

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