linux-kernel - Re: [PATCH] usb: dwc3: gadget: Avoid canceling current request for queuing error

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Date:   Mon, 19 Apr 2021 11:39:26 -0700
From:   Wesley Cheng <wcheng@...eaurora.org>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Felipe Balbi <balbi@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Cc:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jackp@...eaurora.org" <jackp@...eaurora.org>
Subject: Re: [PATCH] usb: dwc3: gadget: Avoid canceling current request for
 queuing error



On 4/15/2021 12:28 PM, Thinh Nguyen wrote:
> Thinh Nguyen wrote:
>> Wesley Cheng wrote:
>>>
>>>
>>> On 4/14/2021 11:26 PM, Felipe Balbi wrote:
>>>> Wesley Cheng <wcheng@...eaurora.org> writes:
>>>>
>>>>> If an error is received when issuing a start or update transfer
>>>>> command, the error handler will stop all active requests (including
>>>>> the current USB request), and call dwc3_gadget_giveback() to notify
>>>>> function drivers of the requests which have been stopped.  Avoid
>>>>> having to cancel the current request which is trying to be queued, as
>>>>> the function driver will handle the EP queue error accordingly.
>>>>> Simply unmap the request as it was done before, and allow previously
>>>>> started transfers to be cleaned up.
>>>>>
>>>>> Signed-off-by: Wesley Cheng <wcheng@...eaurora.org>
>>>>> ---
>>>>>  drivers/usb/dwc3/gadget.c | 5 +++++
>>>>>  1 file changed, 5 insertions(+)
>>>>>
>>>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>>>> index e1b04c97..4200775 100644
>>>>> --- a/drivers/usb/dwc3/gadget.c
>>>>> +++ b/drivers/usb/dwc3/gadget.c
>>>>> @@ -1399,6 +1399,11 @@ static int __dwc3_gadget_kick_transfer(struct dwc3_ep *dep)
>>>>>  		if (ret == -EAGAIN)
>>>>>  			return ret;
>>>>>  
>>>>> +		/* Avoid canceling current request, as it has not been started */
>>>>> +		if (req->trb)
>>>>> +			memset(req->trb, 0, sizeof(struct dwc3_trb));
>>>>
>>>> we don't need a full memset. I think ensuring HWO bit is zero is enough.
>>>>
>>> Hi Felipe,
>>>
>>> Thanks for the input/review, will make this change to just clear the HWO.
>>>
>>
>> Make sure to increment the dequeue pointer also. I think you can use
>> dwc3_gadget_ep_skip_trbs().
>>
> 
> Nevermind. There maybe a problem with using dwc3_gadget_ep_skip_trbs().
> 
> Thinh
> 
Hi Thinh,

Thank you for your input.  In this case (if kick transfer fails w/ an
error), would we still need to mess with the enqueue/dequeue pointers?
Not sure if my assumption is correct, but the TRB wouldn't have been
started, so we can use the same (failed) TRB for future requests, right?

I think one thing I will need to update is to loop through num_trbs and
clear all HWO bits if the above is not needed.

Thanks
Wesley Cheng

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