> No BSP, no kernel source, no vendor documentation — just a DTB extracted from the stock Android firmware and rebuilt from there.

Judging from the build.sh, it looks like this is just using unmodified upstream u-boot and tools from the rockchip-linux repository, so "from scratch" is really just analyzing the DTB to see what drivers need to be loaded?

yes, that is mostly on point. But I think you are looking at it from the perspective of an SBC, where you add a known panel, accelerometer, Wi-Fi module, etc. and already know what components you are integrating.

here the hardware is fixed and undocumented. I didnt modify the tablet, I had to figure out what was inside, what could be supported, where to find missing drivers and how to integrate and debug everything until it actually booted and worked.

I am not claiming to be a C or kernel developer. I am just someone hacking around until the device works. Maybe for others this is trivial, but for me it was a very exciting project.