a bit more explicit about EFI_FLASH_WRITE_THREAD

also borrowing from https://github.com/rusefi/rusefi/pull/6778

firmware/config/stm32f4ems/efifeatures.h

@@ -498,3 +498,7 @@
 #ifndef EFI_SENT_SUPPORT
 #define EFI_SENT_SUPPORT        FALSE
 #endif
+
+#ifndef EFI_FLASH_WRITE_THREAD
+#define EFI_FLASH_WRITE_THREAD FALSE
+#endif

firmware/config/stm32h7ems/efifeatures.h

@@ -42,8 +42,10 @@
 #undef EFI_EMBED_INI_MSD
 #define EFI_EMBED_INI_MSD TRUE
 
+#ifndef EFI_FLASH_WRITE_THREAD
 // H7 has dual bank, so flash on its own (low priority) thread so as to not block any other operations
 #define EFI_FLASH_WRITE_THREAD TRUE
+#endif
 
 #undef ENABLE_PERF_TRACE
 #define ENABLE_PERF_TRACE TRUE

firmware/controllers/flash_main.cpp

@@ -32,6 +32,11 @@
 #define EFI_STORAGE_MFS_EXTERNAL FALSE
 #endif
 
+// Sanity check
+#if (EFI_STORAGE_MFS_EXTERNAL == TRUE) && (EFI_FLASH_WRITE_THREAD == FALSE)
+	#error EFI_FLASH_WRITE_THREAD should be enabled if MFS is used for external flash
+#endif
+
 static bool needToWriteConfiguration = false;
 
 /* if we use ChibiOS MFS for settings */