usb: fix random "null ctrl req" panic when switching usb config

commit 75edff78801711dca40ef6273a26fd9a140d8a03
Author: mojyack <[email protected]>
Date:   Sun Dec 7 21:02:58 2025 +0900

    usb: fix random "null ctrl req" panic when switching usb config
    
    Change-Id: I7839edb99461abfbff03460d63343691085ef34f

diff --git a/firmware/export/usb.h b/firmware/export/usb.h
index 35d525e304..13271652f9 100644
--- a/firmware/export/usb.h
+++ b/firmware/export/usb.h
@@ -240,6 +240,8 @@ void usb_set_mode(int mode);
 /* USB driver call this function to notify that a transfer has completed */
 void usb_signal_transfer_completion(
     struct usb_transfer_completion_event_data *event_data);
+/* Clear all signaled transfer completion events from event queue */
+void usb_clear_pending_transfer_completion_events(void);
 /* notify the USB code that some important event has occurred which influences the
  * USB state (like USB_NOTIFY_SET_ADDR). USB drivers should call usb_core_notify_*
  * functions and not this function. */
diff --git a/firmware/usb.c b/firmware/usb.c
index df87919892..7f4c61a573 100644
--- a/firmware/usb.c
+++ b/firmware/usb.c
@@ -305,6 +305,13 @@ void usb_signal_transfer_completion(
     queue_post(&usb_queue, USB_TRANSFER_COMPLETION, (intptr_t)event_data);
 }
 
+void usb_clear_pending_transfer_completion_events(void)
+{
+    while (queue_peek_ex(&usb_queue, NULL,
+                         1 | QPEEK_REMOVE_EVENTS,
+                         QPEEK_FILTER1(USB_TRANSFER_COMPLETION)));
+}
+
 void usb_signal_notify(long id, intptr_t data)
 {
     queue_post(&usb_queue, id, data);
diff --git a/firmware/usbstack/usb_core.c b/firmware/usbstack/usb_core.c
index 4cf4e1b137..3f2aff4310 100644
--- a/firmware/usbstack/usb_core.c
+++ b/firmware/usbstack/usb_core.c
@@ -863,9 +863,14 @@ static int usb_core_do_set_config(uint8_t new_config)
             }
         }
         init_deinit_endpoints(usb_config - 1, false);
+
+        /* clear any pending transfer completions,
+         * because they are depend on contents of ep_data */
+        usb_clear_pending_transfer_completion_events();
+        /* reset endpoint states */
+        memset(ep_data, 0, sizeof(ep_data));
     }
 
-    memset(ep_data, 0, sizeof(ep_data));
     usb_config = new_config;
     usb_state = usb_config == 0 ? ADDRESS : CONFIGURED;
 
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