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

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Date:   Tue, 4 Apr 2023 10:09:06 +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 4/4/2023 5:19 AM, Thinh Nguyen wrote:
> On Thu, Mar 30, 2023, Krishna Kurapati PSSNV wrote:
>>
>>
>> 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 ?
>>
> 
> Not just in __dwc3_set_mode(). I mean any time dwc3_core_soft_reset
> fails, then we set this flag. So that it can prevent the user calling
> any gadget ops causing more crashes/invalid behavior. The
> dwc->softconnect is already wrong on pullup() on failure.
> 
> So that we can have a check in different gadget ops. For pullup():
> 
> static int dwc3_gadget_pullup() {
> 	if (dwc->udc_is_dead) {
> 		dev_err(dev, "reset me. x_x \n");
> 		return;
> 	}
> 
> 	abc();
> }
> 
> Perhaps the effort is probably the same if we enhance the UDC core for
> this? In any case, I'm fine either way.
> 
> Thanks,
> Thinh

Hi Thinh,

  So you don't want UDC to retry pullup if it fails the first time ? As 
per patch-2 of this series, I was trying to propagate the EITMEDOUT to 
UDC so that the caller (most probably configfs) can take appropriate 
action as to whether it must retry pullup or not.

Regards,
Krishna,