ramips: mt7621: add support for TP-Link ER605 v1

ramips: mt7621: add support for TP-Link ER605 v1

This commit adds support for TP-Link ER605 v1. Like its successor the
ER605 v2, the MAC address can only be found in the tddp partition.

Hardware specifications:
- CPU: MediaTek MT7621DAT (880 MHz, 2 cores)
- CPU type: MIPS 1004Kc
- Flash: 16 MiB (GigaDevice GD25Q127CSIG)
- RAM: 128 MiB
- LAN speed: 1GbE
- LAN ports: 4
- WAN speed: 1GbE
- WAN ports: 1
- Serial: 4-pin header, unpopulated, 3.3V TTL, (115200 8N1)
- Power: 9 VDC, 0.85 A
- LEDs: Power (Green), System (Green)
- Button: RESET

Factory firmware (v1.2.0 Build 20220114 Rel.76871):
root@ER605:~# ubus call system board
{
	"kernel": "3.10.108",
	"hostname": "ER605",
	"system": "MT7621",
	"model": "mtk-apsoc-demo",
	"release": {
		"distribution": "OpenWrt",
		"version": "Barrier Breaker",
		"revision": "unknown",
		"codename": "barrier_breaker",
		"target": "ramips\/generic",
		"description": "OpenWrt Barrier Breaker 14.07"
	}
}

Factory partitions:
0x000000000000-0x000000040000 : "bootloader"
0x000000040000-0x000000070000 : "bootloader-fs"
0x000000070000-0x000000080000 : "extra-para"
0x000000080000-0x000000200000 : "kernel"
0x000000200000-0x000000df0000 : "rootfs"
0x000000df0000-0x000000e10000 : "panic-oops"
0x000000e10000-0x000000e20000 : "partition-table"
0x000000e20000-0x000000e30000 : "device-info"
0x000000e30000-0x000000e40000 : "support-list"
0x000000e40000-0x000000e50000 : "firmware-info"
0x000000e50000-0x000000e60000 : "tddp"
0x000000e60000-0x000000e80000 : "log"
0x000000e80000-0x000001000000 : "rootfs_data"
0x000000000000-0x000001000000 : "firmware"

New OpenWrt partitions:
...
0x000000080000-0x000000df0000 : "firmware"
...
0x000000e80000-0x000001000000 : "rootfs_data_back"

MAC addresses:
 - label/LAN = 'option macaddr' from factory tddp partition
 - WAN = label MAC + 1

Installation:
Split initramfs into 2 parts for writing to the kernel and rootfs
partitions on live device, leave http server up for sysupgrade.

dd if=initramfs-kernel.bin of=kernel-part.bin bs=64k count=24
dd if=initramfs-kernel.bin of=rootfs-part.bin bs=64k skip=24
md5sum kernel-part.bin rootfs-part.bin
python3 -m http.server -d . 8080

Downgrade to TP-Link firmware v1.3.1 or less if running v1.3.2.

From the web UI, open "System Tools" and select "Diagnostics".
Enable "Remote Assistance" and login as root.

tplink_label_mac=01:23:45:67:89:AB
tplink_username=admin
echo -n "$tplink_label_mac$tplink_username" | md5sum | cut -c1-16
ssh \
  -o "KexAlgorithms=+diffie-hellman-group1-sha1" \
  -o "HostKeyAlgorithms=+ssh-rsa" \
  root@192.168.0.1

Download partial initramfs binaries to /tmp and verify checksums match.

cd /tmp
wget http://192.168.0.20:8080/kernel-part.bin
wget http://192.168.0.20:8080/rootfs-part.bin
md5sum kernel-part.bin rootfs-part.bin

Write partial initramfs binaries to kernel and rootfs.

mtd -e kernel write kernel-part.bin kernel
mtd -r -e rootfs write rootfs-part.bin rootfs

Login to OpenWrt initramfs as root.

ssh root@192.168.1.1

Erase firmware partition and perform sysupgrade.

mtd erase firmware
sysupgrade -n -p http://192.168.1.111:8080/squashfs-sysupgrade.bin

Signed-off-by: Charles Joynson <ctjoynson@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/24331
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>