[bobdvb]

HDMI's gate is certification and the ability to then use their marketing brand.

This is absolutely not a technical issue. You can implement the 2.1 spec if you want, you just can't say it's 2.1.

If Valve wanted they could happily get it to work and let people figure out that it works, they just can't use that title in their marketing.

[friendzis]

IIUC the issue is not them being unable to implement 2.1 at all, but rather provide specifically open source implementation. They probably could provide a binary blob.

[bobdvb]

That's probably how NVidia did it.

But there's very little software involved in HDMI, it's mostly hardware and a control API.