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

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Date:   Mon, 27 Feb 2023 19:22:54 -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 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.

Thanks
Wesley Cheng