linux-kernel - Re: [RFC] usb: dwc3: core: Fix RAM interface getting stuck during enumeration

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Message-ID: <bac414a7-aa2a-4b93-82e0-998002c455e0@quicinc.com>
Date:   Fri, 13 Oct 2023 00:09:04 +0530
From:   Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "quic_ppratap@...cinc.com" <quic_ppratap@...cinc.com>,
        "quic_wcheng@...cinc.com" <quic_wcheng@...cinc.com>,
        "quic_jackp@...cinc.com" <quic_jackp@...cinc.com>,
        "quic_ugoswami@...cinc.com" <quic_ugoswami@...cinc.com>
Subject: Re: [RFC] usb: dwc3: core: Fix RAM interface getting stuck during
 enumeration

On 10/12/2023 11:29 PM, Thinh Nguyen wrote:

>> -static int dwc3_gadget_soft_disconnect(struct dwc3 *dwc)
>> +int dwc3_gadget_soft_disconnect(struct dwc3 *dwc)
>>   {
>>   	unsigned long flags;
>>   	int ret;
>> @@ -2701,7 +2701,7 @@ static int dwc3_gadget_soft_disconnect(struct dwc3 *dwc)
>>   	return ret;
>>   }
>>   
>> -static int dwc3_gadget_soft_connect(struct dwc3 *dwc)
>> +int dwc3_gadget_soft_connect(struct dwc3 *dwc)
>>   {
>>   	int ret;
>>   
>> @@ -3963,6 +3963,7 @@ static void dwc3_gadget_disconnect_interrupt(struct dwc3 *dwc)
>>   	dwc3_gadget_dctl_write_safe(dwc, reg);
>>   
>>   	dwc->connected = false;
>> +	dwc->cable_disconnected = true;
>>   
>>   	dwc3_disconnect_gadget(dwc);
>>   
>> @@ -4038,6 +4039,7 @@ static void dwc3_gadget_reset_interrupt(struct dwc3 *dwc)
>>   	 */
>>   	dwc3_stop_active_transfers(dwc);
>>   	dwc->connected = true;
>> +	dwc->cable_disconnected = false;
>>   
>>   	reg = dwc3_readl(dwc->regs, DWC3_DCTL);
>>   	reg &= ~DWC3_DCTL_TSTCTRL_MASK;
>> -- 
>> 2.42.0
>>
> 
> We can just reset the controller when there's End Transfer command
> timeout as a failure recovery. No need to do what you're doing here.
> 
Hi Thinh,

  That was what I initially wanted to do, but there were couple of 
reasons I wanted to take this approach:

1. We can't just reset the controller in midst of gadget_interrupt. We 
need to process it completely and then take action.

2. The above log was seen on QRD variant of SM8550/SM8650 easily. But on
other platforms of same targets, the issue comes up at some other 
instances of code, at a point where no IRQ is running. In such cases its 
not possible to accurately find out code portions and reset the 
controller. The way I confirmed that both platforms are having the same 
issue is:

a. During cable disconnect, I am not receiving disconnect interrupt
b. The reg dump is exactly same in both cases (BMU as well)

So I felt it was better to fix it during cable disconnect because even 
if we remove cable, we are still in device mode only and in this case we 
can unblock suspend and also bring back controller to a known state.

Let me know your thoughts on the above.

Regards,
Krishna,