Add hook to do some flash setup before filesystem init

Author: stonehippo

main.c

@@ -836,6 +836,12 @@ int __attribute__((used)) main(void) {
     // Start the debug serial
     serial_early_init();
 
+    #if CIRCUITPY_EXTERNAL_FLASH_SETUP
+    // Set up anything that might need to get done before we try to use SPI flash
+    // This is needed for some boards where flash relies on GPIO setup to work
+    external_flash_setup();
+    #endif
+
     // Create a new filesystem only if we're not in a safe mode.
     // A power brownout here could make it appear as if there's
     // no SPI flash filesystem, and we might erase the existing one.

py/circuitpy_mpconfig.mk

@@ -49,6 +49,9 @@ CFLAGS += -DMICROPY_PY_USELECT=$(MICROPY_PY_USELECT)
 MICROPY_PY_USELECT_SELECT ?= $(MICROPY_PY_USELECT)
 CFLAGS += -DMICROPY_PY_USELECT_SELECT=$(MICROPY_PY_USELECT_SELECT)
 
+# enable pre-flash GPIO setup
+CIRCUITPY_EXTERNAL_FLASH_SETUP ?= 0
+CFLAGS += -DCIRCUITPY_EXTERNAL_FLASH_SETUP=$(CIRCUITPY_EXTERNAL_FLASH_SETUP)
 
 CIRCUITPY_AESIO ?= $(CIRCUITPY_FULL_BUILD)
 CFLAGS += -DCIRCUITPY_AESIO=$(CIRCUITPY_AESIO)

supervisor/board.h

@@ -47,5 +47,9 @@ void reset_board(void);
 // disabling USB, BLE or flash) because CircuitPython may continue to run.
 void board_deinit(void);
 
+// Configure anything that needs to get set up before the external flash
+// is init'ed. For example, if GPIO needs to be configured to enable the
+// flash chip, as is the case on some boards.
+void external_flash_setup(void);
 
 #endif  // MICROPY_INCLUDED_SUPERVISOR_BOARD_H