ramips: mt7621: add support for Xiaomi Mi Router 4A Gigabit v2

[e323w]

Device is the same as Xiaomi Mi Router 4A Gigabit, except of:

• 5G WiFi is MT7663
• addresses of leds, wifi and eth ports are slightly changed
• at the end of the flash, another Config partition was added, I'm not sure if we should preserve it, but I did it
• patch ramips: mt7621-dts: mux phy0/4 to gmac1 does not seem to work for this device. with him on the wan port there is only Tx traffic, but no Rx. so I didn't add it

Specs:
  SoC:  MT7621
  CPU:  2 x 880 MHz
  ROM:  16 MB
  RAM:  128 MB
  WLAN: MT7603, MT7663

MAC addresses:
  WAN     ****  factory 0xe006 (label)
  LAN     *:f7  factory 0xe000
  2.4 GHz *:f8  factory 0x0000+0x4 (mtd-eeprom+0x4)
  5 GHz   *:f9  factory 0x8000+0x4 (mtd-eeprom+0x4)

Installation:

Factory firmware is based on a custom OpenWrt 17.x.
Installation is the same as for Xiaomi Mi Router 4A Gigabit.

Probably the easiest way to install is to use the script from
this repository: acecilia/OpenWRTInvasion#155

In a more advanced case, you can do everything yourself:
- gain access to the device through one of the exploits described
  in the link above
- upload sysupgrade image to /tmp
- overwrite stock firmware:
  # mtd -e OS1 -r write /tmp/sysupgrade.bin OS1

Recovery:

Recovery procedure is the same as for Xiaomi Mi Router 4A Gigabit.
Possible options can be found here:
https://openwrt.org/inbox/toh/xiaomi/xiaomi_mi_router_4a_gigabit_edition

One of the ways is to use another router with OpenWrt:
- connect both routers by their LAN ports
- download stock firmware from [1]
- place it inside /tmp/test.bin on the main router
- configure PXE/TFTP on the main router
- power off 4Av2, hold Reset button, power on
- as soon as image download via TFTP starts, Reset can be released
- blinking blue wan LED will indicate the end of the flashing process,
  now router can be rebooted
[1] http://cdn.cnbj1.fds.api.mi-img.com/xiaoqiang/rom/r4av2/miwifi_r4av2_firmware_release_2.30.28.bin

in this branch, I split mt7621_xiaomi_mi-router-4a-3g-v2.dtsi into two files: mt7621_xiaomi_mi-router-4a-common.dtsi (with common nodes for all 4a* devices) and original mt7621_xiaomi_mi-router-4a-3g-v2.dtsi (with only 4a-v1 and 3g-v2 specific nodes). it was possible to use the original file, but then the configuration for 4a-v2 would use hacks, including deleting nodes, so why I added this division.

PR based on this work

Signed-off-by: Dmitry Sokolov e323w@proton.me

[csharper2005]

And... Could you add Installation guide, MAC address table, recovery procedure (if you have it in place) to the commit message, please? https://openwrt.org/docs/guide-developer/device-support-policies

[csharper2005]

ramips: mt7621: add support for 'Xiaomi Mi Router 4A Gigabit v2'

Quotation marks can be dropped.

[e323w]

@csharper2005 thank you for the review, I updated commit according to your comments.

[hauke]

Thank you for the pull request, I merged it into master in 39e4f03. I do not know why this is marked closed.