Cannot get any OpenWrt image to run on Zyxel GS1900-8HP (boot loop / reset)

[banane]

I bought it 2nd hand. There is no version number printed on it from the outside. The web interface says "Revision A1", so I guess it's a version 1.

I just noticed that the sudden reset also happens after the line

[ 0.970661] rtl8231_init called, MDIO bus ID: 0

which was mentioned over there as well

Brick Zyxel GS1900-8 - all few seconds boot without lan

The RTL8231 driver should configure all pins as inputs, so it's strange that would trigger the hard reset. According to the info on the wiki, that would be connected to GPIO 5 on the RTL8231. The current driver does change the pins to GPIO before changing them to an input, maybe that's triggering something... A custom build disabling gpio1 in the DTS should leave the GPIO chip alone. Maybe that's a good thing to test first.