Date:   Tue, 17 Aug 2021 01:25:10 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Felipe Balbi <balbi@...nel.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC:     Wesley Cheng <wcheng@...eaurora.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jackp@...eauora.org" <jackp@...eauora.org>
Subject: Re: [RFC][PATCH] usb: dwc3: usb: dwc3: Force stop EP0 transfers
 during pullup disable

Felipe Balbi wrote:
> 
> Hi,
> 
> Thinh Nguyen <Thinh.Nguyen@...opsys.com> writes:
>>> Thinh Nguyen <Thinh.Nguyen@...opsys.com> writes:
>>>>>>>>>>>> If this occurs, then the entire pullup disable routine is skipped and
>>>>>>>>>>>> proper cleanup and halting of the controller does not complete.
>>>>>>>>>>>> Instead of returning an error (which is ignored from the UDC
>>>>>>>>>>>> perspective), do what is mentioned in the comments and force the
>>>>>>>>>>>> transaction to complete and put the ep0state back to the SETUP phase.
>>>>>>>>>>>>
>>>>>>>>>>>> Signed-off-by: Wesley Cheng <wcheng@...eaurora.org>
>>>>>>>>>>>> ---
>>>>>>>>>>>>  drivers/usb/dwc3/ep0.c    | 4 ++--
>>>>>>>>>>>>  drivers/usb/dwc3/gadget.c | 6 +++++-
>>>>>>>>>>>>  drivers/usb/dwc3/gadget.h | 3 +++
>>>>>>>>>>>>  3 files changed, 10 insertions(+), 3 deletions(-)
>>>>>>>>>>>>
>>>>>>>>>>>> diff --git a/drivers/usb/dwc3/ep0.c b/drivers/usb/dwc3/ep0.c
>>>>>>>>>>>> index 6587394..abfc42b 100644
>>>>>>>>>>>> --- a/drivers/usb/dwc3/ep0.c
>>>>>>>>>>>> +++ b/drivers/usb/dwc3/ep0.c
>>>>>>>>>>>> @@ -218,7 +218,7 @@ int dwc3_gadget_ep0_queue(struct usb_ep *ep, struct usb_request *request,
>>>>>>>>>>>>  	return ret;
>>>>>>>>>>>>  }
>>>>>>>>>>>>  
>>>>>>>>>>>> -static void dwc3_ep0_stall_and_restart(struct dwc3 *dwc)
>>>>>>>>>>>> +void dwc3_ep0_stall_and_restart(struct dwc3 *dwc)
>>>>>>>>>>>>  {
>>>>>>>>>>>>  	struct dwc3_ep		*dep;
>>>>>>>>>>>>  
>>>>>>>>>>>> @@ -1073,7 +1073,7 @@ void dwc3_ep0_send_delayed_status(struct dwc3 *dwc)
>>>>>>>>>>>>  	__dwc3_ep0_do_control_status(dwc, dwc->eps[direction]);
>>>>>>>>>>>>  }
>>>>>>>>>>>>  
>>>>>>>>>>>> -static void dwc3_ep0_end_control_data(struct dwc3 *dwc, struct dwc3_ep *dep)
>>>>>>>>>>>> +void dwc3_ep0_end_control_data(struct dwc3 *dwc, struct dwc3_ep *dep)
>>>>>>>>>>>>  {
>>>>>>>>>>>>  	struct dwc3_gadget_ep_cmd_params params;
>>>>>>>>>>>>  	u32			cmd;
>>>>>>>>>>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>>>>>>>>>>> index 54c5a08..a0e2e4d 100644
>>>>>>>>>>>> --- a/drivers/usb/dwc3/gadget.c
>>>>>>>>>>>> +++ b/drivers/usb/dwc3/gadget.c
>>>>>>>>>>>> @@ -2437,7 +2437,11 @@ static int dwc3_gadget_pullup(struct usb_gadget *g, int is_on)
>>>>>>>>>>>>  				msecs_to_jiffies(DWC3_PULL_UP_TIMEOUT));
>>>>>>>>>>>>  		if (ret == 0) {
>>>>>>>>>>>>  			dev_err(dwc->dev, "timed out waiting for SETUP phase\n");
>>>>>>>>>>>> -			return -ETIMEDOUT;
>>>>>>>>>>>> +			spin_lock_irqsave(&dwc->lock, flags);
>>>>>>>>>>>> +			dwc3_ep0_end_control_data(dwc, dwc->eps[0]);
>>>>>>>>>>>> +			dwc3_ep0_end_control_data(dwc, dwc->eps[1]);
>>>>>>>>>>>
>>>>>>>>>>> End transfer command takes time, need to wait for it to complete before
>>>>>>>>>>> issuing Start transfer again. Also, why restart again when it's about to
>>>>>>>>>>> be disconnected.
>>>>>>>>>>
>>>>>>>>>> I can try without restarting it again, and see if that works.  Instead
>>>>>>>>>> of waiting for the command complete event, can we set the ForceRM bit,
>>>>>>>>>> similar to what we do for dwc3_remove_requests()?
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> ForceRM=1 means that the controller will ignore updating the TRBs
>>>>>>>>> (including not clearing the HWO and remain transfer size). The driver
>>>>>>>>> still needs to wait for the command to complete before issuing Start
>>>>>>>>> Transfer command. Otherwise Start Transfer won't go through. If we know
>>>>>>>>> that we're not going to issue Start Transfer any time soon, then we may
>>>>>>>>> be able to get away with ignoring End Transfer command completion.
>>>>>>>>>
>>>>>>>>
>>>>>>>> I see.  Currently, in the place that we do use
>>>>>>>> dwc3_ep0_end_control_data(), its followed by
>>>>>>>> dwc3_ep0_stall_and_restart() which would execute start transfer.  For
>>>>>>>
>>>>>>> That doesn't look right. You can try to see if it can recover from a
>>>>>>> control write request. Often time we do control read and not write.
>>>>>>> (i.e. try to End Transfer and immediately Start Transfer on the same
>>>>>>> direction control endpoint).
>>>>>>>
>>>>>> OK, I can try, but just to clarify, I was referring to how it was being
>>>>>> done in:
>>>>>>
>>>>>> static void dwc3_ep0_xfernotready(struct dwc3 *dwc,
>>>>>> 		const struct dwc3_event_depevt *event)
>>>>>> {
>>>>>> ...
>>>>>> 		if (dwc->ep0_expect_in != event->endpoint_number) {
>>>>>> 			struct dwc3_ep	*dep = dwc->eps[dwc->ep0_expect_in];
>>>>>>
>>>>>> 			dev_err(dwc->dev, "unexpected direction for Data Phase\n");
>>>>>> 			dwc3_ep0_end_control_data(dwc, dep);
>>>>>> 			dwc3_ep0_stall_and_restart(dwc);
>>>>>> 			return;
>>>>>> 		}
>>>>>>
>>>>
>>>> Looking at this snippet again, it looks wrong. For control write
>>>> unexpected direction, if the driver hasn't setup and started the DATA
>>>> phase yet, then it's fine, but there is a problem if it did.
>>>>
>>>> Since dwc3_ep0_end_control_data() doesn't issue End Transfer command to
>>>> ep0 due to the resource_index check, it doesn't follow the control
>>>
>>> IIRC resource_index is always non-zero, so the command should be
>>
>> No, resource_index for ep0out is 0, ep0in is 1. You can check from any
>> of the driver tracepoint log for the return value of Start Transfer
>> command for the resource index of ep0. There could be a mixed up with
>> the undocumented return value of Set Endpoint Transfer Resource command
>> before when this code was written, don't mix up with that.
> 
> fair enough :-)
> 
>>> triggered. If you have access to a Lecroy USB Trainer, could you script
>>> this very scenario for verification?
>>
>> For anyone who wants to work on this, we don't need a LeCroy USB
>> trainer. If you use xhci host, just modify the xhci-ring.c to queue a
>> wrong direction DATA phase TRB of a particular control write request
>> test, and continue with the next control requests.
> 
> That's true.
> 
>>>> transfer flow model in the programming guide. This may cause
>>>> dwc3_ep0_stall_and_restart() to overwrite the TRBs for the DATA phase
>>>> with SETUP stage. Also, if the ep0 is already started, the driver won't
>>>> issue Start Transfer command again.
>>>
>>>> This issue is unlikely to occur unless we see a misbehave host for
>>>> control write request. Regardless, we need to fix this. I may need some
>>>
>>> right, it would be a misbehaving host, however databook called it out as
>>> something that _can_ happen. Moreover, I have vague memories of this
>>> being one of the test cases in Lecroy's USB Certification Suite.
>>
>> Yes, it's something that can happen, and dwc3 should be able to handle
>> it. If you remember which test in particular that tests this, let me
>> know. I want to check how it was passed.
> 
> Unfortunately, not off the top of my head.
> 
>>>> time before I can create a patch and test it. If you or anyone is up to
>>>> take this on, it'd be highly appreciated.
>>>
>>> Before we go ahead writing a patch for this, I'd really like to see
>>> traces showing this failure and a minimal reproducer. The reproducer
>>> would probably have to be a script for Lecroy's USB Trainer.
>>>
>>> Keep in mind this entire ep0 stack used to pass USBCV on every -rc and
>>> major release (before I lost access to all my USB gear heh).
>>>
>>
>> Are you referring to Ch9 USBCV? I don't recall there's a particular test
>> for this.
> 
> No, no. USBCV doesn't have tests for this. Lecroy's Test Suite was more
> extensive than USBCV. I was simply saying that changes to ep0 (and any
> of the low level control pipe handling) should be done with care to make
> sure we don't break certification for folks who'd like to pursue that
> route.
> 

Yes, I agree.

>> There should be a red flag whenever we see End Transfer command
>> immediately follows by a Start Transfer command without any waiting for
>> End Transfer completion. Though, in this case, we don't go through with
>> the End Transfer for ep0 due to the resource_index check in
>> dwc3_ep0_end_control_data().
> 
> Understood. Do you have sample traces showing this case?
> 

No, I'd need to create a test case for it.

BR,
Thinh

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