They don't really have to worry about patent infringement, the biggest issue is that they can implement anything they want, they just can't call it HDMI 2.1 without certification.

That's confusing for the consumer but technically viable.

HDMI exists to write standards, to certify them and to enforce the brand integrity. Patents are a different issue and would be handled separately.

(I am an engineer who spent half his career dealing with this stuff at a technical, legal and commercial level).

> they just can't call it HDMI 2.1 without certification

The problem is more that they can't use the HDMI trademark at all, not just for the HDMI 2.1 on Linux implementation. That makes it a non-starter for AMD or Valve, but in theory should not stop an individual who doesn't care about marketing anything as being HDMI-compatible.