Abstract:
With the steady progress of the development of the next-generation mainline kernel, the upcoming Linux Kernel 7.4 has ushered in a milestone upgrade in the display underlying and graphics driver architecture. According to the open source driver patch merge tree and the latest submitted code, the new kernel officially introduces native AMD FreeSync variable refresh rate (VRR) support to the HDMI interface and the automatic low latency mode (ALLM) that is very core in the HDMI 2.1 specification, completely completing the key functional shortcomings of the Linux platform in modern living room large screens and high-specification game monitors.
For a long time, Linux open source graphics drivers have relatively mature support for adaptive synchronization technology under the DisplayPort (DP) interface. However, players and developers often face many limitations when connecting to large-screen TVs or modern monitors through the HDMI interface. Due to the HDMI Forum's strict closed-source access restrictions on private protocols and specific specifications, the open source community's previous process of adapting HDMI 2.1 high-end features in the mainline driver was extremely bumpy. As a result, many Linux gamers were unable to smoothly turn on anti-tearing and low input lag features under the HDMI channel when connecting to a TV that supports variable refresh rates.
In Linux Kernel 7.4, through the continuous efforts of the AMD open source GPU driver team and the open source community kernel maintainers, substantial breakthroughs have been made in the relevant driver architecture. The new kernel has completed deep reconstruction in the Direct Render Manager (DRM) and AMD GPU Display Core (DC) driver code, enabling the system to directly handshake and enable AMD FreeSync variable refresh rate through the HDMI standard interface. This means that when gamers on the Linux platform connect a compatible HDMI display device, the system can dynamically maintain strict synchronization between the monitor's refresh rate and the actual frame rate output by the graphics card, completely eliminating screen tearing and greatly alleviating the feeling of lag, bringing a silky smooth gaming experience comparable to that in a Windows environment.
In addition to the implementation of FreeSync VRR, the official integration of automatic low latency mode (ALLM) is also attracting attention. As an important part of the HDMI 2.1 specification, ALLM allows the graphics card to automatically send exclusive control signaling to the connected smart TV or supported display when it detects that a 3D full-screen game or low-latency interactive task is running, forcing the device to immediately switch to the exclusive "game mode", thus automatically turning off the heavy image post-processing filters and dynamic compensation frame insertion algorithms inside the TV that cause severe input lag. Once the user exits the game and switches back to desktop work or watching regular streaming videos, the system can seamlessly return to the normal display mode, eliminating the need for users to frequently manually search for menus on the TV remote control to switch image quality modes.
Linux Kernel 7.4's full embrace of HDMI modern display technology is an important watershed for Linux to enter the large-screen living room entertainment and professional PC gaming ecosystem. With the increasing prosperity of handheld operating systems, customized game distributions and open source driver ecosystems based on the Linux kernel, the low latency and adaptive synchronization capabilities under the HDMI channel will not only greatly benefit living room HTPC and high-end gaming PC users, but also clear the underlying protocol obstacles for the entire open source graphics ecosystem to cope with high-resolution, high-refresh rate large-screen interactions.
Relevant patches have been incorporated into the mainline merge test window and are expected to be pushed to major mainstream Linux distributions after the official version of the kernel is finalized:
https://lore.kernel.org/dri-devel/
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