Thanks for posting, 3mdeb Founder here. To some extent, it is known that Root of Trust provisioning tooling for ARM SoC vendors is problematic. Proprietary, closed source, with documentation available only in Chinese. We did that for many ARM SoCs, and as a result, we published some presentations http://hackertimes.com/item?id=43643136

I'm interested in your experience, which AMR SoC has the most Secure boot-friendly ecosystem?

The RISC-V ecosystem is also interesting. Recently, I was looking at Kendryte K230D.