AMD wanted to incorporate parts of the HDMI 2.1 spec into its open-source Linux drivers, but the HDMI Forum's legal beagles shutdown the whole idea

pcgamer.com:

If you're a Linux gamer and use an AMD Radeon graphics card, you might be aware that there are all kinds of limitations and bugs when trying to run at high resolutions with high refresh rates, when using the HDMI port. AMD's software engineers had been working on a solution to it all, by implementing parts of the HDMI 2.1 specification into the code, but sadly had to shelve the whole project because the HDMI Forum rejected the project.

The disappointing news was reported by Phoronix, who spotted a brief explanation of the problem by one of AMD's Linux engineers. If you try to run something like a 4K, 120 Hz display on a Radeon RX 6000/7000 series graphics card, via its HDMI ports, you'll run into problems when using Linux. You wouldn't expect this to happen, because AMD clearly advertises HDMI 2.1 support on all those models.

However, that's only true for Windows-based PCs, as the governing body of the port's specifications (HDMI Forum) doesn't permit its use in open-source software. AMD would be aware of this fact, as it's been a member of the group for a long time. It's not clear what the exact issue is but I strongly suspect that it has to do with the multiple technologies developed by other group members not wanting their work to be open-sourced.

Either that or it's the media companies within the Forum who think that anything to do with open-source will just instantly lead to DRMs being hacked and all their content being instantly pirated.

AMD tried to come to some agreement with the HDMI Forum, probably just including the bare minimum of the HDMI 2.1 spec to solve the high-resolution problem, but ultimately the legal teams involved just put a stop to the whole thing.

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All of this means that Linux gamers with Radeon GPUs will still need to use the