Date:   Sat, 29 Aug 2020 21:35:22 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Wesley Cheng <wcheng@...eaurora.org>,
        "balbi@...nel.org" <balbi@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "jackp@...eaurora.org" <jackp@...eaurora.org>
Subject: Re: [PATCH v2] usb: dwc3: Stop active transfers before halting the
 controller

Wesley Cheng wrote:
> In the DWC3 databook, for a device initiated disconnect or bus reset, the
> driver is required to send dependxfer commands for any pending transfers.
> In addition, before the controller can move to the halted state, the SW
> needs to acknowledge any pending events.  If the controller is not halted
> properly, there is a chance the controller will continue accessing stale or
> freed TRBs and buffers.
>
> Signed-off-by: Wesley Cheng <wcheng@...eaurora.org>
>
> ---
> Changes in v2:
>  - Moved cleanup code to the pullup() API to differentiate between device
>    disconnect and hibernation.
>  - Added cleanup code to the bus reset case as well.
>  - Verified the move to pullup() did not reproduce the problen using the
>    same test sequence.
>
> Verified fix by adding a check for ETIMEDOUT during the run stop call.
> Shell script writing to the configfs UDC file to trigger disconnect and
> connect.  Batch script to have PC execute data transfers over adb (ie adb
> push)  After a few iterations, we'd run into a scenario where the
> controller wasn't halted.  With the following change, no failed halts after
> many iterations.
> ---
>  drivers/usb/dwc3/ep0.c    |  2 +-
>  drivers/usb/dwc3/gadget.c | 52 ++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 52 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/dwc3/ep0.c b/drivers/usb/dwc3/ep0.c
> index 59f2e8c31bd1..456aa87e8778 100644
> --- a/drivers/usb/dwc3/ep0.c
> +++ b/drivers/usb/dwc3/ep0.c
> @@ -197,7 +197,7 @@ int dwc3_gadget_ep0_queue(struct usb_ep *ep, struct usb_request *request,
>  	int				ret;
>  
>  	spin_lock_irqsave(&dwc->lock, flags);
> -	if (!dep->endpoint.desc) {
> +	if (!dep->endpoint.desc || !dwc->pullups_connected) {
>  		dev_err(dwc->dev, "%s: can't queue to disabled endpoint\n",
>  				dep->name);
>  		ret = -ESHUTDOWN;
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 3ab6f118c508..df8d89d6bdc9 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -1516,7 +1516,7 @@ static int __dwc3_gadget_ep_queue(struct dwc3_ep *dep, struct dwc3_request *req)
>  {
>  	struct dwc3		*dwc = dep->dwc;
>  
> -	if (!dep->endpoint.desc) {
> +	if (!dep->endpoint.desc || !dwc->pullups_connected) {
>  		dev_err(dwc->dev, "%s: can't queue to disabled endpoint\n",
>  				dep->name);
>  		return -ESHUTDOWN;
> @@ -1926,6 +1926,24 @@ static int dwc3_gadget_set_selfpowered(struct usb_gadget *g,
>  	return 0;
>  }
>  
> +static void dwc3_stop_active_transfers(struct dwc3 *dwc)
> +{
> +	u32 epnum;
> +
> +	for (epnum = 2; epnum < DWC3_ENDPOINTS_NUM; epnum++) {
> +		struct dwc3_ep *dep;
> +
> +		dep = dwc->eps[epnum];
> +		if (!dep)
> +			continue;
> +
> +		if (!(dep->flags & DWC3_EP_ENABLED))
> +			continue;

Don't do the enabled check here. Let the dwc3_stop_active_transfer() do
that checking.

> +
> +		dwc3_remove_requests(dwc, dep);
> +	}
> +}
> +
>  static int dwc3_gadget_run_stop(struct dwc3 *dwc, int is_on, int suspend)
>  {
>  	u32			reg;
> @@ -1994,9 +2012,39 @@ static int dwc3_gadget_pullup(struct usb_gadget *g, int is_on)
>  		}
>  	}
>  
> +	/*
> +	 * Synchronize and disable any further event handling while controller
> +	 * is being enabled/disabled.
> +	 */
> +	disable_irq(dwc->irq_gadget);

I think it's better to do dwc3_gadget_disable_irq(). This only stops
handling events. Although it's unlikely, the controller may still
generate events before it's halted.

>  	spin_lock_irqsave(&dwc->lock, flags);
> +
> +	/* Controller is not halted until pending events are acknowledged */
> +	if (!is_on) {
> +		u32 reg;
> +
> +		__dwc3_gadget_ep_disable(dwc->eps[0]);
> +		__dwc3_gadget_ep_disable(dwc->eps[1]);

You can just do __dwc3_gadget_stop(), and do that after
dwc3_stop_active_transfers().

> +
> +		/*
> +		 * The databook explicitly mentions for a device-initiated
> +		 * disconnect sequence, the SW needs to ensure that it ends any
> +		 * active transfers.
> +		 */
> +		dwc3_stop_active_transfers(dwc);
> +
> +		reg = dwc3_readl(dwc->regs, DWC3_GEVNTCOUNT(0));
> +		reg &= DWC3_GEVNTCOUNT_MASK;

Can we use another variable "count" instead of reusing reg to make it a
little clearer?

> +		if (reg > 0) {
> +			dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), reg);
> +			dwc->ev_buf->lpos = (dwc->ev_buf->lpos + reg) %
> +						dwc->ev_buf->length;
> +		}
> +	}
> +
>  	ret = dwc3_gadget_run_stop(dwc, is_on, false);
>  	spin_unlock_irqrestore(&dwc->lock, flags);
> +	enable_irq(dwc->irq_gadget);
>  
>  	return ret;
>  }
> @@ -3100,6 +3148,8 @@ static void dwc3_gadget_reset_interrupt(struct dwc3 *dwc)
>  	}
>  
>  	dwc3_reset_gadget(dwc);
> +	/* Stop any active/pending transfers when receiving bus reset */
> +	dwc3_stop_active_transfers(dwc);
>  
>  	reg = dwc3_readl(dwc->regs, DWC3_DCTL);
>  	reg &= ~DWC3_DCTL_TSTCTRL_MASK;

Looks good to me.

Thanks,
Thinh

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