There is a contract between AMD and HDMI Forum covering the licence to use the logo. We don't know the wording, and I am sure it is thousands of pages of dense

There is a contract between AMD and HDMI Forum covering the licence to use the logo. We don't know the wording, and I am sure it is thousands of pages of dense legalise; but it can literally say: "We promise not release a Linux driver compatible with the spec.".