I’ve updated @hammer instructions with recent findings, @r43k3n could you put these instructions into 1st post?
This is how I got LEDE installed. Some of the steps can be done differently. I used this for inspiration https://www.youtube.com/watch?v=CSHNyo5QxaQ
Unbox router
Connect to the router using WiFi
Goto http://192.168.31.1
Go through the wizard to set passwords for the router + wifi
Reconnect to the router using WiFi
Goto http://192.168.31.1
Logon and find the page where you can upgrade the firmware look for a big yellow dot with an “i” inside. You will see the version number of the router and there is a button below where you can browse for a file. Flash miwifi_r3g_firmware_c2175_2.25.122.bin (developer firmware) and wait a few minutes.
Download https://play.google.com/store/apps/details?id=com.xiaomi.router to your phone/tablet (there is also an iOS app)
Open “Mi Wi-Fi” app (and sign-up) and sign-in to your account. Router will be detected and added to your account (assuming you are connected to the WiFi on the router and the routers WAN port is connected to Internet).
On a PC, visit http://d.miwifi.com/rom/ssh and sign-in to you account. You will get to a page that should display your router, the root password and a download button. Hit the button to get miwifi_ssh.bin
Format USB drive using FAT32 and copy miwifi_ssh.bin, lede-ramips-mt7621-mir3g-squashfs-kernel1.bin and lede-ramips-mt7621-mir3g-squashfs-rootfs0.bin to the USB drive
Cut the power the router, put the USB drive in the router, press and hold “reset” button (with a paper-clip), power on the router (while holding reset). When the router starts flashing yellow release the reset button. Wait until router has rebooted and you should (finally…) have SSH access.
Login to the router using SSH using the “root” as username and the (root) “password” from http://d.miwifi.com/rom/ssh
In SSH console
cd /extdisks/sda1 (can be different if you remove and reinsert the usb stick)
mtd write lede-ramips-mt7621-mir3g-squashfs-kernel1.bin kernel1
mtd write lede-ramips-mt7621-mir3g-squashfs-rootfs0.bin rootfs0
nvram set flag_try_sys1_failed=1
nvram commit
reboot
LEDE should be installed and available at 192.168.1.1 (with WiFi disabled I assume)
Upgrading to a newer snapshot can be done using the regular methods (from the command-line using sysupgrade or through LuCI) using lede-ramips-mt7621-mir3g-squashfs-sysupgrade.tar