Valve patches Mesa RADV to enable FP16 for AMD GFX8 GPUs in Steam Play

Valve developer Georg Lehmann merged a patch into Mesa 27.0 that will be back-ported to stable releases. The change enables FP16 format support by default for AMD GFX8 GPUs (GCN 3rd/4th Gen, Tonga through Polaris RX 400/500 series) specifically when running VKD3D-Proton. Previously this required the manual radv_enable_float16_gfx8 option and was disabled by default due to typically neutral or negative performance impact. Newer Windows games are increasingly requiring FP16 support, and the fix resolves issues such as broken SSAO in the recent Witcher 3 update.

What the FP16 change means for GFX8 owners

• Scope: Affects AMD GCN 3rd and 4th generation GPUs from Tonga through Radeon RX 400/500 Polaris cards
• Mechanism: One-line patch enables radv_enable_float16_gfx8 automatically when VKD3D-Proton is detected
• Rationale: Newer D3D12 games are beginning to require FP16 as a baseline capability; without exposure, games fail or render incorrectly
• Performance trade-off: FP16 is deliberately not enabled for all applications because it is typically no faster and sometimes slower than FP32 on this hardware generation
• Known fix: Resolves SSAO (screen-space ambient occlusion) rendering in The Witcher 3 following a recent game update

Why it matters

The patch extends the practical lifespan of 2015-2017 era AMD hardware for Linux gaming, reducing the pressure to upgrade for users running titles through Steam Play's Proton compatibility layer.