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Message-ID: <f334b8b9-b8d8-240d-5ace-bed255f4609a@quicinc.com>
Date:   Wed, 5 Apr 2023 09:54:28 +0530
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Subject: Re: [PATCH v2 1/2] usb: dwc3: gadget: Bail out in pullup if soft
 reset timeout happens
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To:     Thinh Nguyen <Thinh.Nguyen@synopsys.com>
CC:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Alan Stern <stern@rowland.harvard.edu>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Colin Ian King <colin.i.king@gmail.com>,
        Jiantao Zhang <water.zhangjiantao@huawei.com>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "quic_ppratap@quicinc.com" <quic_ppratap@quicinc.com>,
        "quic_wcheng@quicinc.com" <quic_wcheng@quicinc.com>,
        "quic_jackp@quicinc.com" <quic_jackp@quicinc.com>,
        "quic_ugoswami@quicinc.com" <quic_ugoswami@quicinc.com>
References: <20230328160756.30520-1-quic_kriskura@quicinc.com>
 <20230328160756.30520-2-quic_kriskura@quicinc.com>
 <20230328212048.rpm4ly265etahwm3@synopsys.com>
 <0aa1caae-ab09-2ef9-0ec8-3dd01a3f3af0@quicinc.com>
 <20230330001003.rwzo4n2hl6i22vh3@synopsys.com>
 <4f473d08-156a-622f-2ef2-ad11caa7ccda@quicinc.com>
 <20230403234937.sotn3pznu4winlkw@synopsys.com>
 <e769cc7c-8b87-c346-5cef-9d89f3ccb91e@quicinc.com>
 <20230404214347.mi6rmksr7pym74rp@synopsys.com>
From:   Krishna Kurapati PSSNV <quic_kriskura@quicinc.com>
In-Reply-To: <20230404214347.mi6rmksr7pym74rp@synopsys.com>
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On 4/5/2023 3:13 AM, Thinh Nguyen wrote:
> On Tue, Apr 04, 2023, Krishna Kurapati PSSNV wrote:
>>
>>
>> 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@quicinc.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@hu-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.
>>
> 
> Now I'm confused. If the soft-reset times out, that means that the
> soft-reset (self-clearing) bit isn't cleared. How can we retry if it's
> stuck in this state? My impression is that soft-reset would not complete
> at all. Is that not the case for you, or it's simply because we need a
> longer soft-reset timeout?
> 
> Thanks,
> Thinh

Hi Thinh,

   Sorry for not being clear. The intention of patch-1 was to ensure we 
don't start the controller if reset times out and patch-2 was to ensure 
that UDC is in sync with controller by understanding that gadget_connect 
has failed and necessary cleanup has to be done in gadget_bind_driver.

But usually since the UDC_store is the one that is causing pullup to be 
called, the error value is propagated back to UDC_store. If it sees a 
failure, it does a retry to pullup.

I didn't check  whether subsequent retries by UDC to pullup are helping 
clear the reset bit or not. But I thought retrying pullup won't be of 
any harm.

I now get that my patches are incomplete w.r.t handling the timeout.

IIRC one of the following is what you are suggesting we need to do:

Option-1:
Set a flag when reset times out and clear it upon core_exit / core_init. 
If the flag is set, block calls to all the gadget_ops in dwc3. Basically 
even if retry happens from configfs/UDC, we bail out in pullup/udc_start 
even without trying the requested gadget operation.

Option-2:
If gadget_connect fails with -ETIMEDOUT in UDC, handle the failure and 
implement the same flag in UDC and don't even call any gadget_ops.

Regards,
Krishna,