HDMI Forum to AMD: No, you can’t make an open source HDMI 2.1 driver

Any Linux user trying to send the highest-resolution images to a display at the fastest frame rate is out of luck for the foreseeable future, at least when it comes to an HDMI connection.

The licensing group that controls the HDMI standard, the HDMI Forum, has reportedly told AMD that it does not allow an open source implementation of the HDMI 2.1 (or HDMI 2.1+) specification, blocking tools such as AMD’s FreeSync from working over HDMI connections at resolution/rate combinations like 4K at 120 Hz, or 5K at 240 Hz.

Linux blog Phoronix noted in January 2021 that the HDMI Forum did not offer public access to the HDMI 2.1 specification. Alex Deucher, an AMD engineer who has long contributed to the company’s open source offerings, has kept a related bug thread alive for at least two years, only to deliver the negative outcome yesterday.

In February 2023, Deucher reported that he was “working with our [AMD] legal team to sort out what we can deliver while still complying with our obligations to HDMI Forum.” Two months later, he said that AMD got “the basic functionality up and running, now we have to go through each of the features with legal and determine if/how we can expose them while still meeting our obligations.” Summer and fall of 2023 went by, with legal review still underway, and in October, the decision was “in the hands of the HDMI Forum.”

On Wednesday afternoon, Deucher offered the current resolution:

The HDMI Forum has rejected our proposal unfortunately. At this time an open source HDMI 2.1 implementation is not possible without running afoul of the HDMI Forum requirements.

Ars has reached out to the HDMI Forum, AMD, and Deucher for further comment and will update the post with new information. X.org was also reportedly involved in negotiations with the HDMI Forum.

Membership in the HDMI Forum is a minimum of $15,000. While AMD is a listed member, that likely doesn’t extend to offering up an implementation of a specification for public use. The member agreement forbidding such things does not appear to be publicly available, nor does an “addendum” for members linked from the Forum’s site. A source code license found on the Forum’s site does not appear to be particularly flexible.

Phoronix and some commenters have suggested potential interference from media firms concerned about digital video ripping. That would seem like a barn door closed years after the horse’s departure, but it also exists as one explanation, lacking other detail.

This outcome leaves DisplayPort as the likely best option for Linux users needing the best possible output. It also suggests that AMD has to decide whether to implement newer HDMI support inside closed-source Linux drivers or simply point its most demanding customers to other options.