Message-ID: <f760fdcf-cd59-2c71-8c85-a4624620edeb@synopsys.com>
Date:   Fri, 13 Aug 2021 23:21:51 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Wesley Cheng <wcheng@...eaurora.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "balbi@...nel.org" <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@...eauora.org" <jackp@...eauora.org>
Subject: Re: [RFC][PATCH] usb: dwc3: usb: dwc3: Force stop EP0 transfers
 during pullup disable

Wesley Cheng wrote:
> Hi Thinh,
> 
> On 8/12/2021 2:31 PM, Thinh Nguyen wrote:
>> Wesley Cheng wrote:
>>> Hi Thinh,
>>>
>>> On 8/11/2021 5:47 PM, Thinh Nguyen wrote:
>>>> Wesley Cheng wrote:
>>>>> During a USB cable disconnect, or soft disconnect scenario, a pending
>>>>> SETUP transaction may not be completed, leading to the following
>>>>> error:
>>>>>
>>>>>     dwc3 a600000.dwc3: timed out waiting for SETUP phase
>>>>
>>>> How could it be a case of cable disconnect? The pullup(0) only applies
>>>> for soft-disconnect scenario. If the device initiated a disconnect, then
>>>
>>> Thanks for the response.  I guess this is specific for some use cases,
>>> but some applications such as ADB will close the FFS EP files after it
>>> gets the disconnection event, leading to this pullup disable as well.
>>> So its specific to that particular use case.
>>
>> Does that mean that the ADB application won't expect a connection until
>> user intervention or some other notification to do pullup(1)?
>>
> 
> Yes, correct.  The Android USB framework will trigger the pullup(1) again.
> 
>>>
>>>> the driver should wait for the control request to complete. If it times
>>>> out, something is already wrong here. The programming guide only
>>>> mentions that we should wait for completion, but it doesn't say about
>>>> recovery in a case of hung transfer. I need to check internally but it
>>>> should be safe to issue End Transfer.
>>>>
>>>
>>> Yes, what I did was modify a device running the Linux XHCI stack w/o
>>> reading/sending out the SETUP DATA phase, so that on the device end we'd
>>> always run into that situation where there's still a pending EP0 TRB queued.
>>
>> Is this only for validation purpose?
>>
> 
> Yes, just to help verify the fix by injecting the error condition.

Just want to clarify, so you didn't really run into this problem but
want to fix the recovery path right?

> 
>>>
>>> We're running multiple devices with this fix as well, and doing device
>>> initiated disconnect.
>>>
>>>>>
>>>>> 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).

> the most part, we were trying to follow the flow diagram in:
> 
> 	4.4 Control Transfer Programming Model
> 
> We'd technically be in the "wait for host" stage at this point, so hence
> why we issued the end transfer, then followed with the stall and restart.
> 

You're not setting up the data stage on host side right? So, we wouldn't
receive a XferNotReady(data) to proceed to the next state to interpret
whether it's unexpected direction to end and restart. Also, you should
check to see which direction/control stage was hung to issue End
Transfer to ep0 or ep1. On reconnect after device initiated disconnect,
the gadget should start ep0 for setup stage again.

Note:
I don't think we clearly defined a recovery for this timeout for device
initiated disconnect. Most of the time we don't want to issue End
Transfer for endpoint 0 (OUT direction) because we may be expecting a
setup packet. However, in this case of error recovery to proceed to
soft-disconnect, it should be fine.

BR,
Thinh

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