Author here. Got the official repository wrong for NPU firmware. Fixed it now, belongs to user "airockchip" on GitHub and latest commits have been authored by Randall Zhuo from Rockchip, so it seems to be official at least.
I have trouble understanding this part:<p>> Beware, messing out with your clocks via sysfs without knowing what you are doing may permanently damage your device at the hardware level, so if you're clueless, don't mess around.<p>Anyway, very nice and informative article, thanks !
So you ditched the old v4.4 Rockchip vendor kernel in favor of Mainline Linux and now half of your SBC doesn't work! Well, trouble no more, at least I'll help you get a working NPU for accelerated AI inference.