linux-kernel - Re: [PATCH] usb: dwc3: gadget: Add 100uS delay after end transfer command without IOC

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Date:   Tue, 28 Feb 2023 01:36:55 -0800
From:   Wesley Cheng <quic_wcheng@...cinc.com>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "quic_jackp@...cinc.com" <quic_jackp@...cinc.com>
Subject: Re: [PATCH] usb: dwc3: gadget: Add 100uS delay after end transfer
 command without IOC

Hi Thinh,

On 2/27/2023 8:02 PM, Thinh Nguyen wrote:
> On Mon, Feb 27, 2023, Wesley Cheng wrote:
>> Hi Thinh,
>>
>> On 2/27/2023 7:10 PM, Thinh Nguyen wrote:
>>> On Tue, Feb 28, 2023, Thinh Nguyen wrote:
>>>> On Mon, Feb 27, 2023, Wesley Cheng wrote:
>>>>> Previously, there was a 100uS delay inserted after issuing an end transfer
>>>>> command for specific controller revisions.  This was due to the fact that
>>>>> there was a GUCTL2 bit field which enabled synchronous completion of the
>>>>> end transfer command once the CMDACT bit was cleared in the DEPCMD
>>>>> register.  Since this bit does not exist for all controller revisions, add
>>>>> the delay back in.
>>>>>
>>>>> An issue was seen where the USB request buffer was unmapped while the DWC3
>>>>> controller was still accessing the TRB.  However, it was confirmed that the
>>>>> end transfer command was successfully submitted. (no end transfer timeout)
>>>>
>>>> Currently we only check for command active, not completion on teardown.
>>>>
>>>>> In situations, such as dwc3_gadget_soft_disconnect() and
>>>>> __dwc3_gadget_ep_disable(), the dwc3_remove_request() is utilized, which
>>>>> will issue the end transfer command, and follow up with
>>>>> dwc3_gadget_giveback().  At least for the USB ep disable path, it is
>>>>> required for any pending and started requests to be completed and returned
>>>>> to the function driver in the same context of the disable call.  Without
>>>>> the GUCTL2 bit, it is not ensured that the end transfer is completed before
>>>>> the buffers are unmapped.
>>>>>
>>>>> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
>>>>
>>>> This is expected. We're supposed to make sure the End Transfer command
>>>> complete before accessing the request. Usually on device/endpoint
>>>> teardown, the gadget drivers don't access the stale/incomplete requests
>>>> with -ESHUTDOWN status. There will be problems if we do, and we haven't
>>>> fixed that.
>>>>
>>>> Adding 100uS may not apply for every device, and we don't need to do
>>>> that for every End Transfer command. Can you try this untested diff
>>>> instead:
>>>>
>>
>> Thanks for the code suggestion.
>>
>>>>
>>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>>> index 30408bafe64e..5ae5ff4c8858 100644
>>>> --- a/drivers/usb/dwc3/gadget.c
>>>> +++ b/drivers/usb/dwc3/gadget.c
>>>> @@ -1962,6 +1962,34 @@ static int __dwc3_gadget_get_frame(struct dwc3 *dwc)
>>>>    	return DWC3_DSTS_SOFFN(reg);
>>>>    }
>>>> +static int dwc3_poll_ep_completion(struct dwc3_ep *dep)
>>>> +{
>>>> +	if (!list_empty(&dep->started_list)) {
>>>> +		struct dwc3_request *req;
>>>> +		int timeout = 500;
>>>> +
>>>> +		req = next_request(&dep->started_list);
>>>> +		while(--timeout) {
>>>> +			/*
>>>> +			 * Note: don't check the last enqueued TRB in case
>>>> +			 * of short transfer. Check first TRB of a started
>>>> +			 * request instead.
>>>> +			 */
>>>> +			if (!(req->trb->ctrl & DWC3_TRB_CTRL_HWO))
>>>> +				break;
>>>> +
>>>> +			udelay(2);
>>>> +		}
>>>> +		if (!timeout) {
>>>> +			dev_warn(dep->dwc->dev,
>>>> +				 "%s is still in-progress\n", dep->name);
>>>> +			return -ETIMEDOUT;
>>>> +		}
>>>> +	}
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>>>    /**
>>>>     * __dwc3_stop_active_transfer - stop the current active transfer
>>>>     * @dep: isoc endpoint
>>>> @@ -2003,10 +2031,12 @@ static int __dwc3_stop_active_transfer(struct dwc3_ep *dep, bool force, bool int
>>>>    	WARN_ON_ONCE(ret);
>>>>    	dep->resource_index = 0;
>>>> -	if (!interrupt)
>>>> +	if (!interrupt) {
>>>> +		ret = dwc3_poll_ep_completion(dep);
>>>
>>> Actually, the TRB status may not get updated, so this may not work,
>>> instead of polling, may need to add the delay here instead.
>>>
>>
>> Yeah, I just gave it a try, and I get the ETIMEDOUT error all the time.
>> Don't think we can utilize the HWO bit here.
>>
> 
> I may be over complicating things here. With ForceRM, the controller
> only updates the last TRB it processed. We don't care about performance
> much during teardown. That would mean more codes for something that's
> not need.
> 

Yes :) that is what I encountered as well.  I tried a few other things, 
but it opened a whole new set of topics that needed to be discussed 
further.  Hence why I proposed the simple delay, since this happens only 
in the teardown path as you mentioned.


> Can you add a delay here instead? Make sure it's at least 1ms and
> applicable for dwc_usb32 also.
> 

Sure, I will update the delay to 1ms and also add USB32 check.

Thanks
Wesley Cheng