Re: [PATCH v2] usb: dwc3: Stop active transfers before halting the controller

[Thinh Nguyen]

Wesley Cheng wrote:
>
> On 9/1/2020 3:14 PM, Wesley Cheng wrote:
>>
>> On 8/29/2020 2:35 PM, Thinh Nguyen wrote:
>>> 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@xxxxxxxxxxxxxx>
>>>>
>>>> ---
>>>> 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.
>>>
>> Hi Thinh,
>>
>> Thanks for the detailed review, as always.  Got it, we can allow that to
>> catch it based off the DWC3_EP_TRANSFER_STARTED.
>>
>>>> +
>>>> +		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.
>>>
>> I think its better if we can do both.  At least with the disable_irq()
>> call present, we can ensure the irq handlers are complete, or we can do
>> as Felipe suggested, and first disable the controller events (using
>> dwc3_gadget_disable_irq()) and then calling synchronize_irq().
>>
>> The concern I had is the pullup() API updating the lpos, and the hardirq
>> handler referencing it to update the evt buf cache and waking up the
>> threaded irq handler. (since we don't clear the evt->count explicitly,
>> it may reference empty/stale events)

I see, then we should do both.

>>
>>>>  	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().
>>>
>> Got it.
>>
> Hi Thinh,
>
> Maybe we can ignore calling dwc3_gadget_disable_irq() separately if we
> are going to use __dwc3_gadget_stop(), since gadget stop will call
> dwc3_gadget_disable_irq().  Also, it would be executed before the event
> count clearing, so if there was an event (unlikely) that was generated,
> we would discard it.

That was my intention. Just make sure to re-enable the events on pull_up(on)

>
> Something like:
>
> 	disable_irq(dwc->irq_gadget);
> 	spin_lock_irqsave(&dwc->lock, flags);
>
> 	if (!is_on) {
> 		u32 count;
>
> 		dwc3_stop_active_transfers(dwc);
> 		__dwc3_gadget_stop(dwc);
>
> 		count = dwc3_readl(dwc->regs, DWC3_GEVNTCOUNT(0));
> 		count &= DWC3_GEVNTCOUNT_MASK;
>
> Thanks
> Wesley
>
>

Thanks,
Thinh