Date:   Thu, 20 Aug 2020 03:01:22 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Wesley Cheng <wcheng@...eaurora.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "balbi@...nel.org" <balbi@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
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] usb: dwc3: Stop active transfers before halting the
 controller

Wesley Cheng wrote:
> On 8/19/2020 2:42 PM, Thinh Nguyen wrote:
>> Hi,
>>
>> Wesley Cheng wrote:
>>> In the DWC3 databook, for a device initiated disconnect, 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>
>>>
>>> ---
>>> 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.

Btw, we have some sysfs attributes to do soft-connect/disconnect also
/sys/class/udc/<UDC>/soft_connect


>>> ---
>>>  drivers/usb/dwc3/ep0.c    |  2 +-
>>>  drivers/usb/dwc3/gadget.c | 59 +++++++++++++++++++++++++++++++++++++--
>>>  2 files changed, 57 insertions(+), 4 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..1f981942d7f9 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;
>>> +
>>> +		dwc3_remove_requests(dwc, dep);
>>> +	}
>>> +}
>>> +
>>>  static int dwc3_gadget_run_stop(struct dwc3 *dwc, int is_on, int suspend)
>>>  {
>>>  	u32			reg;
>>> @@ -1950,16 +1968,37 @@ static int dwc3_gadget_run_stop(struct dwc3 *dwc, int is_on, int suspend)
>>>  
>>>  		dwc->pullups_connected = true;
>>>  	} else {
>>> +		dwc->pullups_connected = false;
>>> +
>>> +		__dwc3_gadget_ep_disable(dwc->eps[0]);
>>> +		__dwc3_gadget_ep_disable(dwc->eps[1]);
>> run_stop() function shouldn't be doing this. This is done in
>> dwc3_gadget_stop(). Also, if it's device-initiated disconnect, driver
>> needs to wait for control transfers to complete.
>>
> Hi Thinh ,
>
> Thanks for the feedback.

Thanks for the patch :)

>
> We already wait for the ep0state to move to the setup stage before
> running the run stop routine, but events can still be triggered until
> the controller is halted. (which is not started until we attempt to
> write to the DCTL register) The reasoning will be the same as the below
> comment.
>
>>> +
>>> +		/*
>>> +		 * 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);
>> It shouldn't be done here. Maybe move this to the dwc3_gadget_pullup()
>> function. The run_stop() function can be called for other context beside
>> this (e.g. hibernation).
>>
> It was preferred to have it placed after the pullups_connected was set
> to false, so that further ep queues would be blocked (with the added
> check), and we can ensure after the stop active xfers was run, nothing
> could be pending.

It should be fine if you do it inside the spin_lock of the
dwc3_gadget_pullup(). I'm trying to keep the run_stop() function
separate for the context of hibernation. For hibernation, the driver
needs to wait for the end_transfer commands to complete (to save TRBs
state and to resume transfer later). Granted that we can just add a
check "if (!hibernation)" or modify the code later, but I think it's
cleaner this way.

>
> Also, for the hibernation case, the databook mentions that we should
> issue the end transfer routine as well for the hibernation w/ device
> disconnected situation.

That's true, but see my comment above.

>  (I don't believe the current DWC3 gadget driver
> supports the hibernation while device connected case, which has some
> considerations we would need to address)

Right now, the DWC3 driver doesn't handle hibernation at all. I've yet
to push those changes out.

>
>>> +
>>>  		reg &= ~DWC3_DCTL_RUN_STOP;
>>>  
>>>  		if (dwc->has_hibernation && !suspend)
>>>  			reg &= ~DWC3_DCTL_KEEP_CONNECT;
>>> -
>>> -		dwc->pullups_connected = false;
>>>  	}
>>>  
>>>  	dwc3_gadget_dctl_write_safe(dwc, reg);
>>>  
>>> +	/* Controller is not halted until pending events are acknowledged */
>>> +	if (!is_on) {
>>> +		reg = dwc3_readl(dwc->regs, DWC3_GEVNTCOUNT(0));
>>> +		reg &= DWC3_GEVNTCOUNT_MASK;
>>> +		if (reg > 0) {
>>> +			dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), reg);
>>> +			dwc->ev_buf->lpos = (dwc->ev_buf->lpos + reg) %
>>> +						dwc->ev_buf->length;
>>> +		}
>>> +	}
>>> +
>> Driver should handle the events before clearing the run_stop bit, not
>> just acknowledging and ignoring them.
>>
> Do you think its better if we call the dwc3_check_event_buf() and
> dwc3_process_event_buf() here?  That will handle the clearing of the
> events and allow them to be handled.  There are some snippets in the
> databook, which mentions that we don't need to handle/process the
> events, and just acknowledge them. (it mentions this in the hibernation
> section)

I think this should be handle separately from the run_stop() function.
Maybe put it in the pullup() function just for device initiated
disconnect case only.

>
>>>  	do {
>>>  		reg = dwc3_readl(dwc->regs, DWC3_DSTS);
>>>  		reg &= DWC3_DSTS_DEVCTRLHLT;
>>> @@ -1994,9 +2033,15 @@ 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);
>>>  	spin_lock_irqsave(&dwc->lock, flags);
>>>  	ret = dwc3_gadget_run_stop(dwc, is_on, false);
>>>  	spin_unlock_irqrestore(&dwc->lock, flags);
>>> +	enable_irq(dwc->irq_gadget);
>>>  
>>>  	return ret;
>>>  }
>>> @@ -3535,6 +3580,14 @@ static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
>>>  	if (!count)
>>>  		return IRQ_NONE;
>>>  
>>> +	/* Controller is halted; ignore new/pending events */
>>> +	if (!dwc->pullups_connected) {
>>> +		dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), count);
>>> +		dwc->ev_buf->lpos = (dwc->ev_buf->lpos + count) %
>>> +					dwc->ev_buf->length;
>>> +		return IRQ_HANDLED;
>>> +	}
>>> +
>> Why? Are you getting any event after the controller is halted? Also,
>> make sure to take account of hibernation. The controller can get PMU
>> event after halted to bring it out of hibernation.
>>
> We aren't getting any events after the controller is halted, but before
> we go and try to clear the run stop bit.  I added a print in the run
> stop API after clearing the RS bit, and there were pending events in the
> controller at that time.  It might be redundant to have this if we are
> disabling the IRQ already before the run stop call.
>
> I see, so maybe to ensure we don't block the PMU event, we can remove
> this, and rely on the disable_irq() and the run stop API to ensure no
> events will be pending.
>
>>>  	evt->count = count;
>>>  	evt->flags |= DWC3_EVENT_PENDING;
>>>  
>> If you're making these fixes, can you also fix handling reset interrupt
>> ? It also needs to end all the active transfers.
>>
> Sure, I can consider that as well.
>

Thanks,
Thinh

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