[RFC PATCH] usb: dwc3: Ignore late xferNotReady event to prevent halt timeout

[Kuen-Han Tsai <khtsai@google.com>]

During a device-initiated disconnect, an xferNotReady event for an ISOC
IN endpoint can be received after the End Transfer command has already
completed.

This late event incorrectly triggers a new Start Transfer, which
prevents the controller from halting and results in a DSTS.DEVCTRLHLT
bit polling timeout.

Ignore the late xferNotReady event if the controller is already in a
disconnected state.

Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
---
Tracing:

# Stop active transfers by sending End Transfer commands
 android.hardwar-913     [004] d..1.  6172.855517: dwc3_gadget_ep_cmd: ep1out: cmd 'End Transfer' [20d08] params 00000000 00000000 00000000 --> status: Successful
 android.hardwar-913     [004] dn.1.  6172.855734: dwc3_gadget_ep_cmd: ep1in: cmd 'End Transfer' [40d08] params 00000000 00000000 00000000 --> status: Successful
 ...
# Recieve an xferNotReady event on an ISOC IN endpoint
    irq/991-dwc3-29741   [000] D..1.  6172.856166: dwc3_event: event (35d010c6): ep1in: Transfer Not Ready [000035d0] (Not Active)
    irq/991-dwc3-29741   [000] D..1.  6172.856190: dwc3_gadget_ep_cmd: ep1in: cmd 'Start Transfer' [35d60406] params 00000000 ffffb620 00000000 --> status: Successful
 android.hardwar-913     [004] dn.1.  6172.868130: dwc3_gadget_ep_cmd: ep2in: cmd 'End Transfer' [30d08] params 00000000 00000000 00000000 --> status: Timed Out
 ...
# Start polling DSTS.DEVCTRLHLT
 android.hardwar-913     [000] .....  6172.869253: dwc3_gadget_run_stop: start polling DWC3_DSTS_DEVCTRLHLT
 ...
# HALT timeout and show the endpoint status for debugging
 android.hardwar-913     [004] .....  6177.479946: dwc3_gadget_run_stop: finish polling DWC3_DSTS_DEVCTRLHLT, is_on=0, reg=0
 android.hardwar-913     [004] .....  6177.479957: dwc3_gadget_ep_status: ep1out: mps 1024/2765 streams 16 burst 5 ring 64/56 flags E:swbp:>
 android.hardwar-913     [004] .....  6177.479958: dwc3_gadget_ep_status: ep1in: mps 1024/1024 streams 16 burst 2 ring 21/64 flags E:swBp:<
 android.hardwar-913     [004] .....  6177.479959: dwc3_gadget_ep_status: ep2out: mps 1024/2765 streams 16 burst 5 ring 56/48 flags e:swbp:>

---
 drivers/usb/dwc3/gadget.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 25db36c63951..506391699a10 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -3896,7 +3896,8 @@ static void dwc3_endpoint_interrupt(struct dwc3 *dwc,
 		dwc3_gadget_endpoint_transfer_in_progress(dep, event);
 		break;
 	case DWC3_DEPEVT_XFERNOTREADY:
-		dwc3_gadget_endpoint_transfer_not_ready(dep, event);
+		if (dwc->connected)
+			dwc3_gadget_endpoint_transfer_not_ready(dep, event);
 		break;
 	case DWC3_DEPEVT_EPCMDCMPLT:
 		dwc3_gadget_endpoint_command_complete(dep, event);
--
2.50.1.565.gc32cd1483b-goog