Re: [PATCH v3] usb: dwc3: gadget: Prevent EP resource conflicts during StartTransfer

[Selvarasu Ganesan]

On 10/7/2026 7:36 AM, Thinh Nguyen wrote:
> On Tue, Oct 06, 2026, Selvarasu Ganesan wrote:
>>>    	/* Clear out the ep descriptors for non-ep0 */
>>> @@ -1792,9 +1815,9 @@ static int __dwc3_stop_active_transfer(struct dwc3_ep *dep, bool force, bool int
>>>    
>>>    	dep->resource_index = 0;
>>>    
>>> -	if (!interrupt)
>>> +	if (!interrupt || ret)
>>
>> Hi Thinh,
>>
>> Thanks for your code changes. The given code changes look good to me and
>> are working as expected.
>>
>> There is one more concern about an uncovered endpoint resource failure
>> in some corner cases where END TRANSFER timeout is observed (ret = -110).
>>
>> The sequence is explained below,
>>
>> Step 1:
>>    __dwc3_gadget_ep_set_halt(dep, value=0)
>>     ->dwc3_stop_active_transfer(dep, true, true)
> Looks like you still do ForceRM=true. Can you apply this patch:
>
>    b58e6200450d ("usb: dwc3: clear forceRM when issuing EndTransfer")

We have this fix in our dwc3 driver code. but still observing EP end 
transfer timeout.


>
>>       ->END(e.g, ep2out, resource_index=7) issued, but timeout occurs
>>        -> resource_index cleared to 0
>>     ->dwc3_send_clear_stall_ep_cmd(dep)
>>       -> failed to clear STALL on ep2out
>>
>>
>> Step 2:
>> __dwc3_gadget_ep_set_halt(dep, value=0) ->Re triggered clear stall for
>> same EP
>>    -> dwc3_stop_active_transfer(dep, true, true)
>>      -> END(ep2out, resource_index=0) issued (wrong resource!)
>>        -> Command succeeds, DWC3_EP_TRANSFER_STARTED cleared in
>> completion handler
>>
>> Step 3:
>> usb_ep_queue()
>>    -> dwc3_gadget_ep_queue()
>>      -> __dwc3_gadget_kick_transfer()
>>        -> starting = !(dep->flags & DWC3_EP_TRANSFER_STARTED)  -> starting=0
>>          -> Issues STARTTRANSFER (because DWC3_EP_TRANSFER_STARTED is not
>> set)
>>            -> Hardware rejects with NO_RESOURCE (resource 7 still held)
>>
>>
>> Could you please give your suggestions on this issue case?
>>
> Thanks for testing. Can you check whether the End Transfer command ever
> completes with the endpoint completion event after the -ETIMEDOUT error?


No, the endpoint completion event is not seen after the -ETIMEDOUT error.

The proposed fix works well for the __dwc3_gadget_ep_set_halt sequence, 
where DWC3_EP_END_TRANSFER_PENDING must be set to prevent dwc3_ep_queue 
from starting a new transfer during a EP transfer timeout.

But, this is unnecessary for __dwc3_gadget_ep_disable. Since there's no 
way to clear the pending flag if the interrupt is missed and no 
dwc3_ep_queue calls occur until the EP is re-enabled, preserving 
DWC3_EP_END_TRANSFER_PENDING here provides no benefit.
So, the below changes is not necessary in ep disable,

@@ -1096,6 +1110,15 @@ static int __dwc3_gadget_ep_disable(struct 
dwc3_ep *dep)  	 */
  	if (dep->flags & DWC3_EP_DELAY_STOP)
  		mask |= (DWC3_EP_DELAY_STOP | DWC3_EP_TRANSFER_STARTED);
+ + /* + * The End Transfer command is still in progress. Do not clear 
the + * flags, so that the ep is only rearmed once the command 
completes. + */ + if (dep->flags & DWC3_EP_END_TRANSFER_PENDING) + mask 
|= (DWC3_EP_END_TRANSFER_PENDING | + DWC3_EP_TRANSFER_STARTED); +

Instead, keep our suggestion changes that prevent the manipulation of 
dep->flags due to the race condition between dwc3_gadget_ep_disable() 
and dwc3_gadget_ep_queue(), since this race observing in long run rndis 
test.

+ + /* + * When dwc3_gadget_ep_disable() calls dwc3_gadget_giveback(), + 
* the dwc->lock is temporarily released. If dwc3_gadget_ep_queue() + * 
runs in that window it may set the DWC3_EP_TRANSFER_STARTED flag as + * 
part of dwc3_send_gadget_ep_cmd. The original code cleared the flag + * 
unconditionally in the mask operation, which could overwrite the + * 
concurrent modification. + * + * As a workaround for the interrupt 
context constraint where we cannot + * wait for endpoint flushing, 
preserve the DWC3_EP_TRANSFER_STARTED + * flag if it is set, avoiding 
resource conflicts until the framework + * is fixed to properly 
synchronize endpoint lifecycle management. + */ + if (dep->flags & 
DWC3_EP_TRANSFER_STARTED) + mask |= DWC3_EP_TRANSFER_STARTED; +


Thanks,
Selva
> Try with the below.
>
> Thanks,
> Thinh
>
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 1f973e546219..bac0328423cd 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -1819,7 +1819,11 @@ static int __dwc3_stop_active_transfer(struct dwc3_ep *dep, bool force, bool int
>   
>   	dep->resource_index = 0;
>   
> -	if (!interrupt || ret)
> +	if (!interrupt || (ret && ret != -ETIMEDOUT))
>   		dep->flags &= ~DWC3_EP_TRANSFER_STARTED;
>   	else
>   		dep->flags |= DWC3_EP_END_TRANSFER_PENDING;
> @@ -3895,6 +3899,8 @@ static void dwc3_gadget_endpoint_command_complete(struct dwc3_ep *dep,
>   	if (dep->stream_capable)
>   		dep->flags |= DWC3_EP_IGNORE_NEXT_NOSTREAM;
>   
> +	dep->flags &= ~DWC3_EP_DELAY_STOP;
>   	dep->flags &= ~DWC3_EP_END_TRANSFER_PENDING;
>   	dep->flags &= ~DWC3_EP_TRANSFER_STARTED;
>   	dwc3_gadget_ep_cleanup_cancelled_requests(dep);