HDMI FRL Support Achieved With Open-Source Nouveau For NVIDIA GPUs

While the AMDGPU open-source driver has struggled with HDMI 2.1 support due to the HDMI Forum blocking open-source implementations, HDMI Fixed Rate Link (FRL) as a feature of the HDMI 2.1 specification is enjoying success now with the open-source Nouveau graphics driver on Linux for NVIDIA GPUs.

Thanks to the NVIDIA GPU System Processor (GSP) firmware handling much of the HDMI FRL responsibilities, it's possible to implement this functionality in the open-source kernel graphics driver without running into troubles with NVIDIA or the HDMI Forum. This is similar to what we've heard with Intel graphics handling more of their implementation in the binary firmware too.

David Airlie at Red Hat managed to get HDMI FRL working on the Nouveau driver to enable higher refresh rates and resolution modes for this upstream, open-source NVIDIA driver. He's tested this successfully with an Ampere GPU and an HDMI 2.1 capture card.

Airlie commented with the patch series cover letter:

"With GSP the firmware handles most of the hard work, just need to send things in the correct order and handle the link training at the right points."

He also noted the use of Claude Code in helping:

"I used claude code to iterate on this a bunch to solve the ordering issues and align with NVIDIA programming sequences."

These four patches get HDMI FRL going for the Nouveau kernel driver in allowing HDMI connected displays to be driven at higher refresh rates and resolutions than otherwise currently possible. Hopefully this code will be in a state for upstreaming come the Linux v7.2 kernel cycle in the summer.