Date:   Wed, 13 Jul 2022 17:33:43 -0700
From:   Wesley Cheng <quic_wcheng@...cinc.com>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "balbi@...nel.org" <balbi@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "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 4/5] usb: dwc3: Allow end transfer commands to be sent
 during soft disconnect

Hi Thinh,

On 7/13/2022 5:19 PM, Thinh Nguyen wrote:
> On 7/13/2022, Wesley Cheng wrote:
>> Hi Thinh,
>>
>> On 7/12/2022 6:42 PM, Thinh Nguyen wrote:
>>> On 7/12/2022, Wesley Cheng wrote:
>>>> Hi Thinh,
>>>>
>>>> On 7/8/2022 6:58 PM, Thinh Nguyen wrote:
>>>>> On 7/8/2022, Wesley Cheng wrote:
>>>>>> If soft disconnect is in progress, allow the endxfer command to be
>>>>>> sent,
>>>>>> without this, there is an issue where the stop active transfer call
>>>>>> (during pullup disable) wouldn't actually issue the endxfer command,
>>>>>> while clearing the DEP flag.
>>>>>>
>>>>>> In addition, if the DWC3_EP_DELAY_STOP flag was set before soft
>>>>>> disconnect
>>>>>> started (i.e. from the dequeue path), ensure that when the EP0
>>>>>> transaction
>>>>>> completes during soft disconnect, to issue the endxfer with the force
>>>>>> parameter set, as it does not expect a command complete event.
>>>>>>
>>>>>> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
>>>>>> ---
>>>>>>      drivers/usb/dwc3/ep0.c    | 3 +--
>>>>>>      drivers/usb/dwc3/gadget.c | 5 ++++-
>>>>>>      2 files changed, 5 insertions(+), 3 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/usb/dwc3/ep0.c b/drivers/usb/dwc3/ep0.c
>>>>>> index 506ef717fdc0..5851b0e9db0a 100644
>>>>>> --- a/drivers/usb/dwc3/ep0.c
>>>>>> +++ b/drivers/usb/dwc3/ep0.c
>>>>>> @@ -290,8 +290,7 @@ void dwc3_ep0_out_start(struct dwc3 *dwc)
>>>>>>              if (!(dwc3_ep->flags & DWC3_EP_DELAY_STOP))
>>>>>>                  continue;
>>>>>>      -        dwc3_ep->flags &= ~DWC3_EP_DELAY_STOP;
>>>>>> -        dwc3_stop_active_transfer(dwc3_ep, true, true);
>>>>>> +        dwc3_stop_active_transfer(dwc3_ep, true, dwc->connected);
>>>>>>          }
>>>>>>      }
>>>>>>      diff --git a/drivers/usb/dwc3/gadget.c
>>>>>> b/drivers/usb/dwc3/gadget.c
>>>>>> index bd40608b19df..fba2797ad9ae 100644
>>>>>> --- a/drivers/usb/dwc3/gadget.c
>>>>>> +++ b/drivers/usb/dwc3/gadget.c
>>>>>> @@ -3696,8 +3696,10 @@ void dwc3_stop_active_transfer(struct dwc3_ep
>>>>>> *dep, bool force,
>>>>>>          if (dep->number <= 1 && dwc->ep0state != EP0_DATA_PHASE)
>>>>>>              return;
>>>>>>      +    if (interrupt && (dep->flags & DWC3_EP_DELAY_STOP))
>>>>>> +        return;
>>>>>> +
>>>>>>          if (!(dep->flags & DWC3_EP_TRANSFER_STARTED) ||
>>>>>> -        (dep->flags & DWC3_EP_DELAY_STOP) ||
>>>>>>              (dep->flags & DWC3_EP_END_TRANSFER_PENDING))
>>>>>>              return;
>>>>>>      @@ -3744,6 +3746,7 @@ void dwc3_stop_active_transfer(struct
>>>>>> dwc3_ep *dep, bool force,
>>>>>>          __dwc3_stop_active_transfer(dep, force, interrupt);
>>>>>>          spin_lock(&dwc->lock);
>>>>>>      +    dep->flags &= ~DWC3_EP_DELAY_STOP;
>>>>>
>>>>> Can we clear this flag in __dwc3_stop_active_transfer(). It should
>>>>> apply
>>>>> if End Transfer command was sent.
>>>>
>>>> I wanted to make sure that we weren't modifying the DEP flags outside
>>>> of a spin lock.  Patch#3 modifies it where we unlock before calling
>>>> __dwc3_stop_active_transfer(), so we can allow the dwc3 threaded IRQ
>>>> handle events while the cmd status polling happens.
>>>>
>>>> Maybe we can unlock/lock the dwc3->lock inside
>>>> __dwc3_stop_active_transfer() and that way we can ensure DEP flags are
>>>> modified properly?
>>>
>>> I didn't realize that you unlock/lock when calling
>>> __dwc3_stop_active_transfer(). We'd need to be careful if we want to
>>> unlock/lock it, and avoid it all together if possible. It can be easily
>>> overlooked just like dwc3_gadget_giveback().
>>>
>>> What issue did you see without doing this?
>>
>> I saw endxfer timeout issues if I didn't do it.  If we keep the lock
>> held, then the DWC3 event processing would be blocked across the
>> entire time we are waiting for the command act to clear.  With
>> unlocking before polling, then at least we're still able to handle the
>> EP0 events that are pending.
>>
>> It was definitely one of the harder scenarios to reproduce.  The main
>> patch series which resolved a lot of the issues early on was patch#1.
>> After adding that the other issues are seen maybe after a day or so of
>> testing.
>>
> 
> I see. The soft-disconnect still go through right?
> Can you try this and see if this works for you?
> 
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 13e4f1a03417..4f67a484c490 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -451,7 +451,9 @@ int dwc3_send_gadget_ep_cmd(struct dwc3_ep *dep,
> unsigned int cmd,
> 
>           dwc3_writel(dep->regs, DWC3_DEPCMD, cmd);
> 
> -       if (!(cmd & DWC3_DEPCMD_CMDACT)) {
> +       if (!(cmd & DWC3_DEPCMD_CMDACT) ||
> +           (DWC3_DEPCMD_CMD(cmd) == DWC3_DEPCMD_ENDTRANSFER &&
> +            !(cmd & DWC3_DEPCMD_CMDIOC))) {
>                   ret = 0;
>                   goto skip_status;
>           }
> 
> 
> We can set it and forget it when we're about to de-initialize the
> controller. Just like what we've already done by not waiting for the End
> Transfer endpoint command completion interrupt.
> 

I can see this working for the soft disconnect case, but we'll need to 
address it differently for the EP dequeue scenario where IOC/interrupt 
is required to clean up the TRBs.  This is one of the reasons why I went 
with the spinlock approach, since it would apply to both situations.

Thanks
Wesley Cheng

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