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List:       linux-usb
Subject:    Re: [PATCH] usb: dwc3: gadget: Add 100uS delay after end transfer command without IOC
From:       Wesley Cheng <quic_wcheng () quicinc ! com>
Date:       2023-02-28 9:36:55
Message-ID: d01e243e-1ba2-b9cf-2b74-f77f22b5c624 () quicinc ! com
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Hi Thinh,

On 2/27/2023 8:02 PM, Thinh Nguyen wrote:
> On Mon, Feb 27, 2023, Wesley Cheng wrote:
> > Hi Thinh,
> > 
> > On 2/27/2023 7:10 PM, Thinh Nguyen wrote:
> > > On Tue, Feb 28, 2023, Thinh Nguyen wrote:
> > > > On Mon, Feb 27, 2023, Wesley Cheng wrote:
> > > > > Previously, there was a 100uS delay inserted after issuing an end transfer
> > > > > command for specific controller revisions.  This was due to the fact that
> > > > > there was a GUCTL2 bit field which enabled synchronous completion of the
> > > > > end transfer command once the CMDACT bit was cleared in the DEPCMD
> > > > > register.  Since this bit does not exist for all controller revisions, add
> > > > > the delay back in.
> > > > > 
> > > > > An issue was seen where the USB request buffer was unmapped while the DWC3
> > > > > controller was still accessing the TRB.  However, it was confirmed that the
> > > > > end transfer command was successfully submitted. (no end transfer timeout)
> > > > 
> > > > Currently we only check for command active, not completion on teardown.
> > > > 
> > > > > In situations, such as dwc3_gadget_soft_disconnect() and
> > > > > __dwc3_gadget_ep_disable(), the dwc3_remove_request() is utilized, which
> > > > > will issue the end transfer command, and follow up with
> > > > > dwc3_gadget_giveback().  At least for the USB ep disable path, it is
> > > > > required for any pending and started requests to be completed and returned
> > > > > to the function driver in the same context of the disable call.  Without
> > > > > the GUCTL2 bit, it is not ensured that the end transfer is completed before
> > > > > the buffers are unmapped.
> > > > > 
> > > > > Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
> > > > 
> > > > This is expected. We're supposed to make sure the End Transfer command
> > > > complete before accessing the request. Usually on device/endpoint
> > > > teardown, the gadget drivers don't access the stale/incomplete requests
> > > > with -ESHUTDOWN status. There will be problems if we do, and we haven't
> > > > fixed that.
> > > > 
> > > > Adding 100uS may not apply for every device, and we don't need to do
> > > > that for every End Transfer command. Can you try this untested diff
> > > > instead:
> > > > 
> > 
> > Thanks for the code suggestion.
> > 
> > > > 
> > > > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> > > > index 30408bafe64e..5ae5ff4c8858 100644
> > > > --- a/drivers/usb/dwc3/gadget.c
> > > > +++ b/drivers/usb/dwc3/gadget.c
> > > > @@ -1962,6 +1962,34 @@ static int __dwc3_gadget_get_frame(struct dwc3 *dwc)
> > > > 	return DWC3_DSTS_SOFFN(reg);
> > > > }
> > > > +static int dwc3_poll_ep_completion(struct dwc3_ep *dep)
> > > > +{
> > > > +	if (!list_empty(&dep->started_list)) {
> > > > +		struct dwc3_request *req;
> > > > +		int timeout = 500;
> > > > +
> > > > +		req = next_request(&dep->started_list);
> > > > +		while(--timeout) {
> > > > +			/*
> > > > +			 * Note: don't check the last enqueued TRB in case
> > > > +			 * of short transfer. Check first TRB of a started
> > > > +			 * request instead.
> > > > +			 */
> > > > +			if (!(req->trb->ctrl & DWC3_TRB_CTRL_HWO))
> > > > +				break;
> > > > +
> > > > +			udelay(2);
> > > > +		}
> > > > +		if (!timeout) {
> > > > +			dev_warn(dep->dwc->dev,
> > > > +				 "%s is still in-progress\n", dep->name);
> > > > +			return -ETIMEDOUT;
> > > > +		}
> > > > +	}
> > > > +
> > > > +	return 0;
> > > > +}
> > > > +
> > > > /**
> > > > * __dwc3_stop_active_transfer - stop the current active transfer
> > > > * @dep: isoc endpoint
> > > > @@ -2003,10 +2031,12 @@ static int __dwc3_stop_active_transfer(struct dwc3_ep \
> > > > *dep, bool force, bool int  WARN_ON_ONCE(ret);
> > > > 	dep->resource_index = 0;
> > > > -	if (!interrupt)
> > > > +	if (!interrupt) {
> > > > +		ret = dwc3_poll_ep_completion(dep);
> > > 
> > > Actually, the TRB status may not get updated, so this may not work,
> > > instead of polling, may need to add the delay here instead.
> > > 
> > 
> > Yeah, I just gave it a try, and I get the ETIMEDOUT error all the time.
> > Don't think we can utilize the HWO bit here.
> > 
> 
> I may be over complicating things here. With ForceRM, the controller
> only updates the last TRB it processed. We don't care about performance
> much during teardown. That would mean more codes for something that's
> not need.
> 

Yes :) that is what I encountered as well.  I tried a few other things, 
but it opened a whole new set of topics that needed to be discussed 
further.  Hence why I proposed the simple delay, since this happens only 
in the teardown path as you mentioned.


> Can you add a delay here instead? Make sure it's at least 1ms and
> applicable for dwc_usb32 also.
> 

Sure, I will update the delay to 1ms and also add USB32 check.

Thanks
Wesley Cheng


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