Phoronix discovered AMD may be dropping support for Coreboot. The company supported Coreboot as an optional open-source firmware to replace the proprietary UEFI/BIOS, but it seems Coreboot support is missing from the next-gen platform because one of AMD's key partners in the Coreboot project went bankrupt last year:
While many recent generations of past AMD CPU/APUs have worked with Coreboot, it's not clear going forward. One of AMD's key partners in supporting Coreboot, Sage Electronic Engineering, went out of business last year. It was a few months ago that Sage went bust, but it was quiet and I didn't even realize it until a Phoronix reader recently mentioned that fact.
Sage Electronic is now no more and was frequently cited by AMD as their contractor for Coreboot work. Sage's web-site is no longer active, but their final blog post about shutting down can be found here. Since Sage Electronic Engineering closed up shop, at least we've seen some commits by a few AMD engineers.