AMDGPU Driver Lacks HDMI 2.1 While AMD-Xilinx Driver Has Some HDMI 2.1 Support

Those following Phoronix and the open-source AMD Linux kernel graphics driver know that the HDMI Forum has prevented AMD from implementing HDMI 2.1 support in their open-source "AMDGPU" driver as due the driver implementation would run afoul to the organization's licensing requirements. It's been pointed out online this week that the AMD-Xilinx DRM driver though does have some HDMI 2.1 support albeit different hardware.

DRM co-maintainer David Airlie of Red Hat pointed out on Mastodon today that while AMD has no HDMI 2.1 upstream support, a "different part" of AMD has HDMI 2.1 in their open-source driver at least concerning Fixed Rate Link (FRL) training.

Indeed within currently out-of-tree code for the AMD-Xilinx DRM driver there is this HDMI code with indeed mentioning HDMI 2.1 at least around the Fixed Rate Link (FRL) handling.

The AMD-Xilinx "Xlnx" DRM driver is for supporting the ZynqMP / AMD Versal integrated display controller found with some of their SoCs. It doesn't overlap with AMDGPU or rely on AMD Radeon graphics IP, or at least not currently.

As Karol Herbst of Red Hat commented after analyzing the code, it's likely with the AMD-Xilinx hardware they have more of the HDMI 2.1 functionality implemented in firmware/hardware as opposed to the current Radeon hardware needing more of it implemented in the driver and that's where it runs into issues with the HDMI Forum as it would be an open-source driver. This situation with AMD-Xilinx and HDMI 2.1 is likely similar to on the open-source NVIDIA driver side where relying on NVIDIA's (closed-source) firmware for HDMI 2.1 functionality would likely work out; see the article Nouveau Supporting HDMI 2.1 Won't Hopefully Be Too Challenging Thanks To NVIDIA Firmware for that summary of the situation.

So while it may be making the rounds that one part of AMD may support HDMI 2.1 in open-source, underneath it's different hardware/firmware. Short of the HDMI Forum changing stance or future Radeon GPUs punting more of their HDMI 2.1+ implementation to firmware/hardware, there likely is no near-term changes for HDMI 2.1 support in the AMDGPU Linux kernel driver.