Valve-Sponsored Collabora Effort Ports Mesa's Open-Source RADV Vulkan Driver to Windows, Already Running Counter-Strike 2

Overview

Valve is sponsoring an experimental effort by open-source consultancy Collabora to bring RADV — the open-source Mesa Vulkan driver for AMD graphics cards — to Microsoft Windows, according to Collabora and Phoronix. The early-stage port has already reached a working milestone: it can launch the game Counter-Strike 2, as confirmed by Collabora, Phoronix, and Linuxiac.

What We Know

RADV is the open-source Vulkan driver for AMD GPUs built inside the Mesa graphics stack. On Linux, it has become the primary Vulkan driver for AMD hardware, after AMD discontinued their proprietary PAL-based alternative in favor of consolidating efforts around Mesa. According to Phoronix, RADV is also the driver underpinning much of the AMD-powered Steam Deck’s success, and Valve already funds multiple developers who work on RADV and other parts of the Linux graphics stack.

On Windows, AMD GPU owners have so far had to rely solely on AMD’s proprietary driver. The new project, detailed in a blog post by Collabora engineer Louis-Francis Ratté-Boulianne, aims to bring the same open-source Vulkan implementation to Windows, an approach the post says offers “a unified codebase, simplified debugging capabilities, accelerated bug fixes, and community pathways for contribution,” according to Collabora.

The work builds on earlier groundwork laid by graphics developer Faith Ekstrand, who first demonstrated that RADV could talk to AMD’s proprietary Windows kernel driver at XDC 2024, according to Collabora, the annual X.Org Developers Conference. Ekstrand built a tool called wddm2-pdd-re to log the Windows Display Driver Model 2 (WDDM2) calls and the private, vendor-specific data exchanged between AMD’s user-mode and kernel-mode drivers, and used it to reverse-engineer enough of that interface to get RADV submitting work to the proprietary kernel driver — a proof of concept that, per Collabora, topped out at displaying a rotating 3D model.

Collabora’s current phase, sponsored by Valve, pushes that proof of concept much further. Per Collabora and confirmed independently by Linuxiac, the team removed the prior dependency on Windows Subsystem for Linux (WSL), reduced hardcoding tied to specific hardware, and improved command-stream handling, synchronization, sparse bindings, tessellation, task-shader support, and dynamic GPU property querying. The most visible result: the driver can now launch Counter-Strike 2 on Windows using the -vulkan command-line argument, as reported by Collabora and Linuxiac.

The port is not close to production quality. Linuxiac reports that the driver has not yet passed full Vulkan conformance testing, and Collabora lists several unresolved technical obstacles. Development so far has happened on newer AMD hardware — a Radeon RX 7900 XT — while Ekstrand’s earlier work used a Radeon RX 7800 XT, and architectural differences between the two caused hangs during more complex operations, according to the Collabora post. Compiling Mesa’s code with Microsoft’s MSVC compiler, instead of the GCC or Clang toolchains Mesa was built around, also produces subtle bugs, since MSVC handles certain enum types differently — sometimes treating them as signed and capping them at 32 bits.

A deeper structural problem, per Collabora, is that the driver still has to communicate with AMD’s proprietary Windows kernel driver through D3DKMT calls carrying “private driver data — opaque, vendor-specific blobs whose contents are entirely up to the driver,” and those private data structures can change between AMD driver releases with no backward-compatibility guarantee. Collabora’s blog post states that reaching production readiness will require either “a stable, documented interface to the proprietary kernel-mode driver, or a shim library that mediates communication with the KMD through the private data channel.” Phoronix independently describes the same fork in the road, writing that the team needs “a stable and documented interface to the AMD kernel graphics driver on Windows or to create a shim library.”

Performance is also unfinished. The current implementation only supports slower CPU-based image presentation rather than native DXGI swapchains; adding proper DXGI support would require importing D3D12 images, which involves yet more undocumented vendor metadata. Collabora’s post estimates that a full zero-copy presentation path, if AMD and Microsoft were to cooperate on it, could yield up to a 3x performance improvement for applications that are not bottlenecked by the GPU itself, according to Collabora and Linuxiac.

The experimental code lives on a development branch on Collabora’s GitLab, not in Mesa’s main codebase, and neither Collabora nor Valve has announced a timeline for a stable release, according to Linuxiac.

What We Don’t Know

It is not yet clear whether AMD or Microsoft will provide the documented kernel interface Collabora says the project ultimately needs, or whether the team will instead have to build and maintain a reverse-engineered shim library. Neither Valve nor Collabora has said how much engineering time or budget is committed beyond this initial phase, nor what the eventual target audience for a Windows RADV driver would be.

Analysis

The project’s significance lies less in its current state — an experimental driver that struggles with anything beyond a single game launched from the command line — and more in what it represents for Valve’s long-running investment in the open-source Linux graphics stack. Valve has funded RADV development for years as part of its push behind the Steam Deck, and an open, cross-platform Vulkan driver would let the same codebase, and the same bug fixes, serve both Linux and Windows AMD users rather than leaving Windows owners solely dependent on AMD’s closed driver releases.