linux-kernel - Re: [PATCH] usb: dwc3: gadget: Add 100uS delay after end transfer command without IOC

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Message-ID: <20230228031027.ghrfnda5lkt7qfmt@synopsys.com>
Date:   Tue, 28 Feb 2023 03:10:42 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Wesley Cheng <quic_wcheng@...cinc.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>
Subject: Re: [PATCH] usb: dwc3: gadget: Add 100uS delay after end transfer
 command without IOC

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@...cinc.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:
> 
> 
> 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.

>  		dep->flags &= ~DWC3_EP_TRANSFER_STARTED;
> -	else if (!ret)
> +	} else if (!ret) {
>  		dep->flags |= DWC3_EP_END_TRANSFER_PENDING;
> +	}
>  
>  	dep->flags &= ~DWC3_EP_DELAY_STOP;
>  	return ret;
> 
> 

Thanks,
Thinh