linux-kernel - Re: [PATCH v2 1/2] usb: dwc3: gadget: Bail out in pullup if soft reset timeout happens

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Message-ID: <4f473d08-156a-622f-2ef2-ad11caa7ccda@quicinc.com>
Date:   Thu, 30 Mar 2023 22:28:32 +0530
From:   Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Colin Ian King <colin.i.king@...il.com>,
        Jiantao Zhang <water.zhangjiantao@...wei.com>,
        "Rafael J . Wysocki" <rafael@...nel.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: [PATCH v2 1/2] usb: dwc3: gadget: Bail out in pullup if soft
 reset timeout happens



On 3/30/2023 5:40 AM, Thinh Nguyen wrote:
> On Wed, Mar 29, 2023, Krishna Kurapati PSSNV wrote:
>>
>>
>> On 3/29/2023 2:50 AM, Thinh Nguyen wrote:
>>> Hi,
>>>
>>> On Tue, Mar 28, 2023, Krishna Kurapati wrote:
>>>> If the core soft reset timeout happens, avoid setting up event
>>>> buffers and starting gadget as the writes to these registers
>>>> may not reflect when in reset and setting the run stop bit
>>>> can lead the controller to access wrong event buffer address
>>>> resulting in a crash.
>>>>
>>>> Signed-off-by: Krishna Kurapati <quic_kriskura@...cinc.com>
>>>> ---
>>>>    drivers/usb/dwc3/gadget.c | 5 ++++-
>>>>    1 file changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>>> index 3c63fa97a680..f0472801d9a5 100644
>>>> --- a/drivers/usb/dwc3/gadget.c
>>>> +++ b/drivers/usb/dwc3/gadget.c
>>>> @@ -2620,13 +2620,16 @@ static int dwc3_gadget_pullup(struct usb_gadget *g, int is_on)
>>>>    		 * device-initiated disconnect requires a core soft reset
>>>>    		 * (DCTL.CSftRst) before enabling the run/stop bit.
>>>>    		 */
>>>> -		dwc3_core_soft_reset(dwc);
>>>> +		ret = dwc3_core_soft_reset(dwc);
>>>> +		if (ret)
>>>> +			goto done;
>>>>    		dwc3_event_buffers_setup(dwc);
>>>>    		__dwc3_gadget_start(dwc);
>>>>    		ret = dwc3_gadget_run_stop(dwc, true, false);
>>>>    	}
>>>> +done:
>>>>    	pm_runtime_put(dwc->dev);
>>>>    	return ret;
>>>> -- 
>>>> 2.40.0
>>>>
>>>
>>> I think there's one more place that may needs this check. Can you also
>>> add this check in __dwc3_set_mode()?
>>
>> Hi Thinh,
>>
>>    Sure. Will do it.
>> Will the below be good enough ? Or would it be good to add an error/warn log
>> there>
> 
> There's already a warning message in dwc3_core_soft_reset() if it fails.
> 
>>
>> kriskura@...kriskura-hyd:/local/mnt/workspace/krishna/skales2/skales/kernel$
>> git diff drivers/usb/
>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>> index 476b63618511..8d1d213d1dcd 100644
>> --- a/drivers/usb/dwc3/core.c
>> +++ b/drivers/usb/dwc3/core.c
>> @@ -210,7 +210,9 @@ static void __dwc3_set_mode(struct work_struct *work)
>>                  }
>>                  break;
>>          case DWC3_GCTL_PRTCAP_DEVICE:
>> -               dwc3_core_soft_reset(dwc);
>> +               ret = dwc3_core_soft_reset(dwc);
>> +               if (ret)
>> +                       goto out;
>>
>>                  dwc3_event_buffers_setup(dwc);
>>
> 
> If soft-reset failed, the controller is in a bad state. We should not
> perform any further operation until the next hard reset. We should flag
> the controller as dead. I don't think we have the equivalent of the
> host's HCD_FLAG_DEAD. It may require some work in the UDC core. Perhaps
> we can flag within dwc3 for now and prevent any further operation for a
> simpler fix.
> 
Hi Thinh,

  Are you referring that if __dwc3_set_mode failed with core soft reset 
timing out, the caller i.e., dwc3_set_mode who queues the work need to 
know that the operation actually failed. So we can add a flag to 
indicate that gadget is dead and the caller of dwc3_set_mode can check 
the flag to see if the operation is successful or not.

Or am I misunderstanding your comment ?

Regards,
Krishna,