linux-kernel - Re: [PATCH] usb: dwc3: gadget: Stall and restart EP0 if host is unresponsive

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Date:   Tue, 4 Apr 2023 15:23:12 -0700
From:   Wesley Cheng <quic_wcheng@...cinc.com>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "quic_jackp@...cinc.com" <quic_jackp@...cinc.com>,
        "quic_ugoswami@...cinc.com" <quic_ugoswami@...cinc.com>
Subject: Re: [PATCH] usb: dwc3: gadget: Stall and restart EP0 if host is
 unresponsive

Hi Thinh,

On 4/4/2023 3:16 PM, Thinh Nguyen wrote:
> On Tue, Apr 04, 2023, Wesley Cheng wrote:
>> Hi Thinh,
>>
>> On 4/3/2023 6:11 PM, Thinh Nguyen wrote:
>>> On Fri, Mar 31, 2023, Wesley Cheng wrote:
>>>> It was observed that there are hosts that may complete pending SETUP
>>>> transactions before the stop active transfers and controller halt occurs,
>>>> leading to lingering endxfer commands on DEPs on subsequent pullup/gadget
>>>> start iterations.
>>>
>>> Can you clarify this a bit further? Even though the controller is
>>> halted, you still observed activity?
>>>
>>
>> Yes...I didn't understand how that was possible either, but traces clearly
>> showed that the controller halt was successful even though there were no
>> endxfers issued on some EPs.  Although, I can't say for certain if those EPs
>> were actively being used at that time.
>>
> 
> The controller should only be halted after the (non-ep0) endpoints are
> disabled.
> 
> "even though there were no endxferx issued on some EPs", which EPs are
> you referring to? If there's no End Transfer issued while the endpoints
> are active and started during disconnect, we need to fix that in the
> driver.
> 

Sorry let me clarify.  When I said there were no endxfers issued, I 
meant that they were pending (DWC3_EP_DELAY_STOP is set for those EPs). 
  However, since the host wasn't moving the EP0 state forward, we never 
moved back to the SETUP phase, which is where we flush any pending end 
transfers.

void dwc3_ep0_out_start(struct dwc3 *dwc)
{
...
	for (i = 2; i < DWC3_ENDPOINTS_NUM; i++) {
		struct dwc3_ep *dwc3_ep;

		dwc3_ep = dwc->eps[i];
		if (!dwc3_ep)
			continue;

		if (!(dwc3_ep->flags & DWC3_EP_DELAY_STOP))
			continue;

		dwc3_ep->flags &= ~DWC3_EP_DELAY_STOP;
		if (dwc->connected)
			dwc3_stop_active_transfer(dwc3_ep, true, true);
		else
			dwc3_remove_requests(dwc, dwc3_ep, -ESHUTDOWN);
	}
}

This is part of the reason for moving the wait_for_completion() call 
until AFTER the stop active transfers, since that is the point at which 
we could potentially set the DWC3_EP_DELAY_STOP.  If there is a host not 
moving the EP0 state, then we can at least utilize the timeout path to 
force EP0 back to the setup phase.

Thanks
Wesley Cheng