AMD has taken a crucial step to address a long-standing limitation for Radeon GPUs on Linux: modern HDMI 2.1 support within the open-source AMDGPU driver. While full HDMI 2.1 functionality isn’t yet fully realized, AMD has submitted an initial set of official patches to incorporate HDMI Fixed Rate Link (FRL) into the Linux kernel’s graphics driver. FRL is a key component of the HDMI 2.1 standard, enabling it to surpass the legacy TMDS link found in HDMI 2.0 and achieve the bandwidth necessary for more demanding resolutions and refresh rates.
It is reported that the advent of HDMI 2.1 support is a result of Valve secretly pressuring AMD. Valve has a clear vested interest in ensuring AMD hardware is compatible with HDMI 2.1 on Linux, as it directly impacts SteamOS, their upcoming Steam Machines, and any future devices designed to work seamlessly with modern televisions. For a living room PC, HDMI 2.1 is considerably more important than DisplayPort. It’s worth noting that Valve has also previously implemented VRAM optimizations on Linux.
Modern AMD Radeon GPUs Will Finally Have Native Support for the HDMI 2.1 Interface
Until now, this situation has been particularly frustrating for AMD Radeon users on Linux. For years, AMD has been unable to implement full HDMI 2.1 support in its open-source driver due to restrictions imposed by the HDMI Forum. In fact, in February 2024, it was confirmed that the HDMI Forum had rejected AMD’s proposal to release an open-source implementation of HDMI 2.1. This left Linux users limited to DisplayPort or incomplete solutions.
The series of patches submitted by AMD alters this narrative, but it’s important to understand their current impact. Reports indicate that the patches add HDMI FRL to the AMDGPU driver and have passed a significant portion of HDMI compliance tests, with full validation still pending. Furthermore, AMD has clarified that Display Stream Compression (DSC) and Variable Refresh Rate (VRR) are still under testing and will be implemented later.
This means that, for now, we are not looking at a complete HDMI 2.1 stack. The initial submission covers high-speed data transport, which is the foundation for leveraging modern displays with high resolutions and high refresh rates. However, crucial components like DSC, VRR, and other optional features associated with the HDMI 2.1 ecosystem are still missing.
Is Valve Truly Behind This Move?
For context, Valve initially announced the Steam Machine as a device featuring DisplayPort 1.4 and HDMI 2.0 connectivity, despite discussions about whether the hardware could support more. Steam’s own product page lists HDMI 2.0 among its video outputs, and other analyses explained that Valve had managed to announce 4K at 120 Hz via HDMI. To achieve this, they had to make compromises, such as chroma subsampling (a color compression technique), rather than a full HDMI 2.1 implementation in SteamOS.
If AMD successfully integrates full HDMI 2.1 into AMDGPU, the Steam Machine could eventually offer much closer HDMI 2.1 support under SteamOS. This wouldn’t necessarily require a hardware change, but rather a software, driver, and validation update. In essence, the hardware supports it, and the limitation lies with the SteamOS (Linux) operating system. This is why Valve is credited with discreetly exerting pressure for AMD to implement these enhancements, which would be highly beneficial for the Steam Machine and, for example, a future Steam Deck 2 connected to a television.
Currently, a Steam Machine with HDMI 2.0 offers a limited 4K high refresh rate experience. When saturating the bandwidth, certain sacrifices must be made to offer this high resolution and refresh rate, including reducing color information (4:2:2 or 4:2:0). However, HDMI 2.1 utilizing FRL would allow for increased bandwidth up to 48 Gbps with Ultra High Speed cables. This not only enables 4K at 120 Hz but also supports active HDR and provides higher image quality configurations and VRR, which is essential for gaming.
