Use busybox devmem

busybox_config_fragment

@@ -4,3 +4,25 @@ CONFIG_NC=y
 CONFIG_NC_EXTRA=y
 CONFIG_NC_SERVER=y
 CONFIG_STAT=y
+
+# On ARM, with our lkmc_platform_device:
+#
+#     devmem 0x101e9000 w 0x12345678
+#
+# Then on QEMU monitor, notice that the registers don't actually change value:
+#
+#     xp/4 0x101e9000
+#
+# Uses /dev/mem.
+#
+# See also:
+#
+# - https://superuser.com/questions/71389/what-is-dev-mem/1214662#1214662
+# - https://unix.stackexchange.com/questions/4948/shell-command-to-read-device-registers
+# - man mem
+#
+# TODO: why with mmap MAP_PRIVATE (used in my previous custom naive version),
+# the entire register page is read?;
+#
+# TODO: have a look at: https://github.com/kaiwan/device-memory-readwrite
+CONFIG_DEVMEM=y