In order to make work my R9 290, I've modified the following kexts:
- AMD8000Controller.kext (twice, as said in this guide);
- AMDRadeonX4000.kext (as said in this guide);
- AMDRadeonX4000HWServices.kext (adding GPU id, 0x67B11002, in the right place, but now I can't verify exactly the line where I've added it).
I've installed whatevergreen, lilu and all required kexts. Now all works natively, WITHOUT any clover inject and setting external GPU (R9 290) as primary in the BIOS, so screen is visible during boot. Displayed name in system info is "Radeon 8xxx" (or something similar), but GPU acceleration works without any problem. I hope this can help.