linux-kernel - Re: [PATCH v2 2/2] usb: dwc3: Wait for control tranfer completed when stopping gadget

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Message-ID: <CAMz4kuLFtsJBkzihUkkqXp3P=EnFMW8T+pzaK5AZLeQOVH--fA@mail.gmail.com>
Date:   Mon, 19 Sep 2016 18:42:45 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Felipe Balbi <balbi@...nel.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 2/2] usb: dwc3: Wait for control tranfer completed when
 stopping gadget

Hi Felipe,

On 19 September 2016 at 17:58, Felipe Balbi <balbi@...nel.org> wrote:
>
> Hi,
>
> Baolin Wang <baolin.wang@...aro.org> writes:
>>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>>> index 1a33308..c9026ce 100644
>>>> --- a/drivers/usb/dwc3/gadget.c
>>>> +++ b/drivers/usb/dwc3/gadget.c
>>>> @@ -1441,6 +1441,15 @@ static int dwc3_gadget_run_stop(struct dwc3 *dwc, int is_on, int suspend)
>>>>       if (pm_runtime_suspended(dwc->dev))
>>>>               return 0;
>>>>
>>>> +     /*
>>>> +      * Per databook, when we want to stop the gadget, if a control transfer
>>>> +      * is still in process, complete it and get the core into setup phase.
>>>> +      */
>>>> +     if (!is_on && dwc->ep0state != EP0_SETUP_PHASE) {
>>>> +             reinit_completion(&dwc->ep0_completed);
>>>
>>> this seems unnecessary to me. Also, why return here so the caller has to
>>
>> We should re-init the completion due to it will complete control
>> transfer many times before we try to stop gadget.
>
> not sure I get this comment, care to furter explain what you mean?

Sorry for confusing comment. What I mean is it will issue
'complete(&dwc->ep0_completed)' when one control transfer is
completed, and it will increase the completion->done when every
'complete()' function is issued.

If there are seveal control transfers are completed (completion->done
is not 0 bow) and dwc->ep0state is not in EP0_SETUP_PHASE satus when
we want to stop gadget, then we should wait for completion. If we
don't call 'reinit_completion(&dwc->ep0_completed)' (it will reset
completion->done as 0 ), it will not wait for 500ms in
wait_for_completion_timeout() funtion. Hope I make it clear.

>
>>> wait? You could just have called wait_for_completion() here straight
>>> away:
>>>
>>>         if (!is_on && dwc->ep0state != EP0_SETUP_PHASE) {
>>>                 /* should this be interruptible? */
>>>                 ret = wait_for_completion_timeout(&dwc->ep0_in_setup,
>>>                                 msecs_to_jiffies(500));
>>>                 if (ret == 0) {
>>>                         dwc3_trace(trace_dwc3_gadget, "RUN/STOP timeout");
>>>                         return -ETIMEDOUT;
>>>                 }
>>>         }
>>>
>>> There's also no need for that "try_again" trickery. We either can halt
>>> the controller within 500ms or we cannot.
>>
>> But this is in atomic context and we can not issue
>> wait_for_completion_timeout() in atomic context, then we should just
>> return here.
>
> heh, good point. Missed that :-)

OK:)

-- 
Baolin.wang
Best Regards