u-boot fw_setenv WZR-HP-G300NH OpenWRT

openwrt_u-boot_env.sh

cat /proc/mtd 
# dev:    size   erasesize  name
# mtd0: 00040000 00020000 "u-boot"
# mtd1: 00020000 00020000 "u-boot-env"
# mtd2: 01f60000 00020000 "firmware"
# mtd3: 00200000 00020000 "kernel"
# mtd4: 01d60000 00020000 "rootfs"
# mtd5: 01a40000 00020000 "rootfs_data"
# mtd6: 00020000 00020000 "user_property"
# mtd7: 00020000 00020000 "art"

cat <<EOF > /etc/fw_env.config 
#MTD device name        Device offset   Env. size       Flash sector size
/dev/mtd1               0x40000         0x20000         0x20000
EOF

opkg install kmod-mtd-rw
insmod mtd-rw i_want_a_brick=1
dmesg | grep mtd
# [ 2988.051401] mtd-rw: mtd1: setting writeable flag

fw_printenv tftp_wait
## tftp_wait=4

fw_printenv accept_open_rt_fmt
# accept_open_rt_fmt=1

fw_setenv tftp_wait 5
## Can't open /dev/mtd1: Permission denied
## Error: can't write fw_env to flash

## :-/