mediatek: add UBI layout for TP-Link BE450

mediatek: add UBI layout for TP-Link BE450

Add an OpenWrt U-Boot ("UBI") layout variant for the TP-Link Archer
BE450. It replaces the vendor bootloader and the stock dual-image
layout with a single large UBI partition, extending the usable flash
to around 95 MiB, and ships a current U-Boot with TFTP recovery.

Hardware
--------
SoC:    MediaTek MT7988D (Filogic 880)
Wi-Fi:  MediaTek MT7992AV (BE7200, 2.4/5 GHz)
Flash:  128 MiB SPI-NAND
RAM:    512 MiB DDR4
Serial: 115200 8N1, header located next to the heatsink:

heatsink
|   |
|   |
|   |     +----+-----+------+-------+               +-----------------+
|   |     | TX |  RX |  GND | +3.3V |               | power connector |
+---+     +----+-----+------+-------+               +-----------------+
                                  |
                Don't connect ----+

MAC addresses
-------------
The label MAC (base) is stored in tp_data/default-mac and is written
into the factory partition at offset 0x4 during installation:

eth0 (LAN): base (factory 0x4)
eth1 (WAN): base + 1
eth2 (LAN): base + 2
Wi-Fi:      derived by mt76 from the factory EEPROM (2.4 GHz = base,
            5 GHz = base with bit 0x10 set), matching the stock
            layout behaviour.

Installation
------------
Requires a serial connection and a TFTP server. The device must be
running the stock-layout OpenWrt (tplink_be450) build.

1. From the running stock-layout OpenWrt, back up the vendor
   bootloader and the calibration/MAC data. These cannot be
   recovered otherwise:

     cat /dev/mtd0 > /tmp/boot.bin
     cat /dev/mtd5 > /tmp/tp_data.bin
     scp /tmp/boot.bin /tmp/tp_data.bin user@pc:backup/
     scp -r /tmp/tp_data user@pc:backup/

   Store boot.bin, tp_data.bin and the tp_data file contents
   (MT7992_EEPROM.bin, default-mac) somewhere safe.

2. Boot the UBI-layout initramfs. Connect the PC to one of the LAN ports
   (LAN1-3) and serve the recovery image from a TFTP server on the PC at
   192.168.1.2. Interrupt the vendor U-Boot on the serial console
   (Ctrl+C), then:

     setenv serverip 192.168.1.2
     tftpboot 0x50000000 openwrt-mediatek-filogic-tplink_be450-ubi-initramfs-recovery.itb
     bootm 0x50000000

3. Copy the required files to the booted initramfs (192.168.1.1):

     scp -O MT7992_EEPROM.bin default-mac \
       openwrt-mediatek-filogic-tplink_be450-ubi-bl31-uboot.fip \
       openwrt-mediatek-filogic-tplink_be450-ubi-preloader.bin \
       openwrt-mediatek-filogic-tplink_be450-ubi-squashfs-sysupgrade.itb \
       root@192.168.1.1:/tmp

4. Build the factory image from the EEPROM and MAC data:

     cd /tmp
     dd if=/dev/zero bs=$((0x100000)) count=1 | tr '\000' '\377' > factory.bin
     dd if=MT7992_EEPROM.bin of=factory.bin bs=1 count=$((0x1e00)) conv=notrunc
     dd if=default-mac of=factory.bin bs=1 seek=4 conv=notrunc

5. Create the UBI volumes. Warning: this permanently erases the
   remaining vendor data, including tp_data - only proceed with the
   backups from step 1 stored safely:

     ubidetach -p /dev/mtd2
     ubiformat /dev/mtd2 -y
     ubiattach -p /dev/mtd2
     ubimkvol /dev/ubi0 -N fip -t static -s 2MiB
     ubiupdatevol /dev/ubi0_0 /tmp/openwrt-mediatek-filogic-tplink_be450-ubi-bl31-uboot.fip
     ubimkvol /dev/ubi0 -N ubootenv -s 0x1f000
     ubimkvol /dev/ubi0 -N ubootenv2 -s 0x1f000

6. Write the factory data and the BL2 preloader. kmod-mtd-rw is
   required to lift the read-only protection of the bl2 partition;
   set up internet access first or upload the package manually:

     apk update && apk add kmod-mtd-rw
     insmod mtd-rw i_want_a_brick=1
     mtd erase factory
     mtd write /tmp/factory.bin factory
     mtd erase bl2
     mtd write /tmp/openwrt-mediatek-filogic-tplink_be450-ubi-preloader.bin bl2

7. Flash the system:

     sysupgrade -n /tmp/openwrt-mediatek-filogic-tplink_be450-ubi-squashfs-sysupgrade.itb

Revert to stock firmware
------------------------
1. From the UBI-layout OpenWrt, force-flash the stock-layout OpenWrt
   (tplink_be450) initramfs image; the board name differs, so
   sysupgrade must be forced:

     sysupgrade -F -n openwrt-mediatek-filogic-tplink_be450-initramfs-kernel.bin

2. After booting into that initramfs, set up network access, copy
   boot.bin and tp_data.bin from the backup to /tmp and restore the
   vendor bootloader and data:

     apk update && apk add kmod-mtd-rw
     insmod mtd-rw i_want_a_brick=1
     mtd erase boot
     mtd write /tmp/boot.bin boot
     mtd erase ubi0
     mtd erase ubi1
     mtd erase userconfig
     mtd erase tp_data
     mtd write /tmp/tp_data.bin tp_data

3. Verify the tp_data restore before rebooting - without it the
   device has no ethernet:

     md5sum /tmp/tp_data.bin
     md5sum /dev/mtd5

   If the checksums match, reboot. The vendor U-Boot web recovery
   comes up on 192.168.1.1; flash the TP-Link stock firmware from
   there.

Signed-off-by: Emre Yavuzalp <emreyavuzalp2@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/23211
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>