storage: map_file - require the port hook instead of a weak default

A port that sets CIRCUITPY_STORAGE_MAP_FILE now has to define
port_internal_flash_xip_address(); there is no weak fallback returning
NULL. Both ports that set it - raspberrypi and espressif - already
define it, and espressif still returns NULL for a partition it could
not map, so the caller's NULL path keeps its meaning. Setting the flag
without the function is a link error rather than a module that builds
and then refuses every call at runtime.

Author: lynt-smitka

py/circuitpy_mpconfig.mk

@@ -636,8 +636,9 @@ CFLAGS += -DCIRCUITPY_STORAGE=$(CIRCUITPY_STORAGE)
 CIRCUITPY_STORAGE_EXTEND ?= $(CIRCUITPY_DUALBANK)
 CFLAGS += -DCIRCUITPY_STORAGE_EXTEND=$(CIRCUITPY_STORAGE_EXTEND)
 
-# storage.map_file(): read a file straight out of memory-mapped flash. Ports whose CIRCUITPY drive
-# is memory-mapped implement port_internal_flash_xip_address() and turn it on.
+# storage.map_file(): read a file straight out of memory-mapped flash. A port whose CIRCUITPY drive
+# is memory-mapped implements port_internal_flash_xip_address() and turns this on; turning it on
+# without that function is a link error, not a silent no-op.
 CIRCUITPY_STORAGE_MAP_FILE ?= 0
 CFLAGS += -DCIRCUITPY_STORAGE_MAP_FILE=$(CIRCUITPY_STORAGE_MAP_FILE)
 

supervisor/shared/flash.c

@@ -150,12 +150,6 @@ static mp_uint_t flash_read_blocks(mp_obj_t self_in, uint8_t *dest, uint32_t blo
 }
 
 #if CIRCUITPY_STORAGE_MAP_FILE
-MP_WEAK const uint8_t *port_internal_flash_xip_address(uint32_t block, uint32_t *contiguous) {
-    (void)block;
-    (void)contiguous;
-    return NULL;                                // this port does not map its drive
-}
-
 // The sector -> block translation of flash_read_blocks(); FatFs has already validated the
 // cluster chain, so every sector it hands over lies inside the volume.
 const uint8_t *supervisor_flash_xip_address(uint32_t fatfs_sector, uint32_t *contiguous) {

supervisor/shared/internal_flash.h

@@ -11,6 +11,7 @@ void port_internal_flash_flush(void);
 
 #if CIRCUITPY_STORAGE_MAP_FILE
 // The memory-mapped address of a drive block, NULL if the port cannot map it; *contiguous
-// receives how many blocks from it are contiguous in the mapping. Weak NULL default.
+// receives how many blocks from it are contiguous in the mapping. A port that sets
+// CIRCUITPY_STORAGE_MAP_FILE implements this.
 const uint8_t *port_internal_flash_xip_address(uint32_t block, uint32_t *contiguous);
 #endif