Date:   Thu, 6 Apr 2023 07:44:49 +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 4/6/2023 6:15 AM, Thinh Nguyen wrote:
> On Wed, Apr 05, 2023, Krishna Kurapati PSSNV wrote:
>>
>>
>> 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@...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.
>>>>
>>>
>>> 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.
> 
> That should still be there.
> 
>>
>> 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.
> 
> It's fine to retry. I'm thinking that the controller is in a bad state
> at this point that we can't recover (hopefully that's not the case).
> 
>>
>> 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.
>>
> 
Hi Thinh,

Thanks for the review.

> I'm thinking of option-1. For option-2, we can't control if the
> gadget_ops will be called. We only have control how we will respond in
> case they get called again.
> 
> But now I'm thinking again, I think it may be ok without adding the
> flag. The UDC core and gadget driver won't do anything else before
> pullup(1) is successful. Calling other gadget_ops should be harmless
> (ie. it won't crash/break the system)?
> 
I can give this a try in long run testing (For 7-14 days) and see if 
anything else is breaking.

Most probably we do a composition switch / PIPO in between which can 
call usb_gadget_unregister_driver which might invoke a pullup(0) 
followed by udc_stop() and like you mentioned must not be a problem.

> Sorry for the noise, but I think it may be ok without marking the
> controller dead. I wonder if we can confirm my suspiction on retry? I
> believe this is not easy to reproduce on your setup? If not, I think we
> can take your change as is.
> 
Regards,
Krishna,

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