diff --git a/drivers/mtd/chips/Kconfig b/drivers/mtd/chips/Kconfig
index 3b3dabce58de..bbfa1f129266 100644
--- a/drivers/mtd/chips/Kconfig
+++ b/drivers/mtd/chips/Kconfig
@@ -115,6 +115,7 @@ config MTD_MAP_BANK_WIDTH_16
 
 config MTD_MAP_BANK_WIDTH_32
 	bool "Support 256-bit buswidth" if MTD_CFI_GEOMETRY
+	select MTD_COMPLEX_MAPPINGS if HAS_IOMEM
 	default n
 	help
 	  If you wish to support CFI devices on a physical bus which is
diff --git a/include/linux/mtd/map.h b/include/linux/mtd/map.h
index 5e0eb7ccabd4..3aa56e3104bb 100644
--- a/include/linux/mtd/map.h
+++ b/include/linux/mtd/map.h
@@ -122,18 +122,13 @@
 #endif
 
 #ifdef CONFIG_MTD_MAP_BANK_WIDTH_32
-# ifdef map_bankwidth
-#  undef map_bankwidth
-#  define map_bankwidth(map) ((map)->bankwidth)
-#  undef map_bankwidth_is_large
-#  define map_bankwidth_is_large(map) (map_bankwidth(map) > BITS_PER_LONG/8)
-#  undef map_words
-#  define map_words(map) map_calc_words(map)
-# else
-#  define map_bankwidth(map) 32
-#  define map_bankwidth_is_large(map) (1)
-#  define map_words(map) map_calc_words(map)
-# endif
+/* always use indirect access for 256-bit to preserve kernel stack */
+# undef map_bankwidth
+# define map_bankwidth(map) ((map)->bankwidth)
+# undef map_bankwidth_is_large
+# define map_bankwidth_is_large(map) (map_bankwidth(map) > BITS_PER_LONG/8)
+# undef map_words
+# define map_words(map) map_calc_words(map)
 #define map_bankwidth_is_32(map) (map_bankwidth(map) == 32)
 #undef MAX_MAP_BANKWIDTH
 #define MAX_MAP_BANKWIDTH 32