dwc2: guard EP0 status completion with armed ZLP state

Track when an EP0 OUT zero-length transfer is actually armed and require that state before synthesizing a status-stage completion ahead of a co-reported SETUP event.

This preserves the validated status-before-SETUP ordering fix while avoiding stale zero-length state from producing spurious EP0 OUT completions.

Author: Alex-Schaefer

src/portable/synopsys/dwc2/dcd_dwc2.c

@@ -62,6 +62,7 @@ static xfer_ctl_t xfer_status[DWC2_EP_MAX][2];
 typedef struct {
   // EP0 transfers are limited to 1 packet - larger sizes has to be split
   uint16_t ep0_pending[2];  // Index determines direction as tusb_dir_t type
+  bool ep0_out_zlp_armed;   // EP0 OUT ZLP transfer is armed and waiting for completion
   uint16_t dfifo_top;      // top free location in DFIFO in words
 
   // Number of IN endpoints active
@@ -665,6 +666,9 @@ bool dcd_edpt_xfer(uint8_t rhport, uint8_t ep_addr, uint8_t* buffer, uint16_t to
     // EP0 can only handle one packet
     if (epnum == 0) {
       _dcd_data.ep0_pending[dir] = total_bytes;
+      if (dir == TUSB_DIR_OUT) {
+        _dcd_data.ep0_out_zlp_armed = (total_bytes == 0);
+      }
     }
 
     // Schedule packets to be sent within interrupt
@@ -744,6 +748,9 @@ static void handle_bus_reset(uint8_t rhport) {
 
   tu_memclr(xfer_status, sizeof(xfer_status));
 
+  _dcd_data.ep0_pending[TUSB_DIR_OUT] = 0;
+  _dcd_data.ep0_pending[TUSB_DIR_IN] = 0;
+  _dcd_data.ep0_out_zlp_armed = false;
   _dcd_data.sof_en = false;
   _dcd_data.allocated_epin_count = 0;
 
@@ -949,12 +956,16 @@ static void handle_epout_slave(uint8_t rhport, uint8_t epnum, dwc2_doepint_t doe
   xfer_ctl_t* xfer = XFER_CTL_BASE(epnum, TUSB_DIR_OUT);
   const bool ep0_status_complete_before_setup = (epnum == 0) && doepint_bm.setup_phase_done &&
                                                 doepint_bm.xfer_complete &&
+                                                _dcd_data.ep0_out_zlp_armed &&
                                                 (_dcd_data.ep0_pending[TUSB_DIR_OUT] == 0) &&
                                                 (xfer->total_len == 0);
 
   if (doepint_bm.setup_phase_done) {
     if (ep0_status_complete_before_setup) {
+      _dcd_data.ep0_out_zlp_armed = false;
       dcd_event_xfer_complete(rhport, epnum, 0, XFER_RESULT_SUCCESS, true);
+    } else if (epnum == 0) {
+      _dcd_data.ep0_out_zlp_armed = false;
     }
 
     // Cleanup previous pending EP0 IN transfer if any
@@ -976,6 +987,9 @@ static void handle_epout_slave(uint8_t rhport, uint8_t epnum, dwc2_doepint_t doe
         // EP0 can only handle one packet, Schedule another packet to be received.
         edpt_schedule_packets(rhport, epnum, TUSB_DIR_OUT);
       } else {
+        if (epnum == 0) {
+          _dcd_data.ep0_out_zlp_armed = false;
+        }
         dcd_event_xfer_complete(rhport, epnum, xfer->total_len, XFER_RESULT_SUCCESS, true);
       }
     }
@@ -1017,12 +1031,16 @@ static void handle_epout_dma(uint8_t rhport, uint8_t epnum, dwc2_doepint_t doepi
   xfer_ctl_t* xfer = XFER_CTL_BASE(epnum, TUSB_DIR_OUT);
   const bool ep0_status_complete_before_setup = (epnum == 0) && doepint_bm.setup_phase_done &&
                                                 doepint_bm.xfer_complete &&
+                                                _dcd_data.ep0_out_zlp_armed &&
                                                 (_dcd_data.ep0_pending[TUSB_DIR_OUT] == 0) &&
                                                 (xfer->total_len == 0);
 
   if (doepint_bm.setup_phase_done) {
     if (ep0_status_complete_before_setup) {
+      _dcd_data.ep0_out_zlp_armed = false;
       dcd_event_xfer_complete(rhport, epnum, 0, XFER_RESULT_SUCCESS, true);
+    } else if (epnum == 0) {
+      _dcd_data.ep0_out_zlp_armed = false;
     }
 
     // Cleanup previous pending EP0 IN transfer if any
@@ -1058,6 +1076,9 @@ static void handle_epout_dma(uint8_t rhport, uint8_t epnum, dwc2_doepint_t doepi
           dma_setup_prepare(rhport);
         }
 
+        if (epnum == 0) {
+          _dcd_data.ep0_out_zlp_armed = false;
+        }
         dcd_dcache_invalidate(xfer->buffer, xfer->total_len);
         dcd_event_xfer_complete(rhport, epnum, xfer->total_len, XFER_RESULT_SUCCESS, true);
       }