For folks that have lost their soldering irons, I created a "firmware" file that exploits a memory safety bug in the S4 bootloader web recovery to allow unsigned openwrt firmware to be tftp uploaded without serial access: https://drive.google.com/uc?export=download&id=1Szb5G5iWWnKNk8BOfs0i2cVAnv3oN9d1
Installation:
- run tftp server on pc with static ip 192.168.0.2
- place openwrt "initramfs-kernel.bin" image in tftp root dir
- connect pc to router ethernet port1
- while holding in reset button on bottom of router, power on router
- from pc access router webgui at http://192.168.0.1
- upload deco_s4_faux_fw_tftp.bin
- router will load and execture in-memory openwrt
- switch pc back to dhcp or static 192.168.1.x
- flash openwrt sysupgrade image via luci/ssh at 192.168.1.1