linux-kernel - Re: [PATCH 4/5] usb: dwc3: Allow end transfer commands to be sent during soft disconnect

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Date:   Wed, 13 Jul 2022 01:42:23 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Wesley Cheng <quic_wcheng@...cinc.com>,
        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

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?

Thanks,
Thinh