stm32/usbdev: Optionally pass through vendor requests to Setup function.

Signed-off-by: Damien George <damien@micropython.org>

ports/stm32/usbd_conf.h

@@ -49,6 +49,11 @@
 #endif
 #define USBD_DEBUG_LEVEL                      0
 
+// Whether the core USBD driver passes through vendor device requests to the class implementation.
+#ifndef USBD_ENABLE_VENDOR_DEVICE_REQUESTS
+#define USBD_ENABLE_VENDOR_DEVICE_REQUESTS    (0)
+#endif
+
 // For MCUs with a device-only USB peripheral
 #define USBD_PMA_RESERVE                      (64)
 #define USBD_PMA_NUM_FIFO                     (16) // Maximum 8 endpoints, 2 FIFOs each

ports/stm32/usbdev/core/src/usbd_ctlreq.c

@@ -120,6 +120,14 @@ USBD_StatusTypeDef  USBD_StdDevReq (USBD_HandleTypeDef *pdev , USBD_SetupReqType
 {
   USBD_StatusTypeDef ret = USBD_OK;
 
+  #if USBD_ENABLE_VENDOR_DEVICE_REQUESTS
+  // Pass through vendor device requests directly to the implementation.
+  // It must call `USBD_CtlError(pdev, req);` if it does not respond to the request.
+  if ((req->bmRequest & 0xe0) == 0xc0) {
+    return pdev->pClass->Setup (pdev, req);
+  }
+  #endif
+
   switch (req->bRequest)
   {
   case USB_REQ_GET_DESCRIPTOR: