Copyright, patent, trademark, and trade secret laws are all entirely different and have almost nothing to do with each other (don’t be fooled by the property-rights-hating shysters who try to gaslight you into lumping them all as “intellectual property[sic]”).
Trademarks and patents don’t have the same kinds of interoperability exceptions that copyright does, and you can’t claim to “support HDMI™” without licensing rights to those in addition to whatever copyrighted code you might need for the software side of the implementation.
freeman@sh.itjust.works 4 days ago
AMD is a member of the HDMI consortium and is probably bound by private agreements to not make open source drivers without permission from the consortium. They did try to get them to budge but they didn’t.