Backends/DRM: add --prefer-drm (independent scanout device) for hybrid/eGPU#11
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relil wants to merge 1 commit into
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Backends/DRM: add --prefer-drm (independent scanout device) for hybrid/eGPU#11relil wants to merge 1 commit into
relil wants to merge 1 commit into
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Decouple the DRM/KMS scanout device from the Vulkan render device. init_drm() derives the KMS node from the chosen Vulkan physical device (vulkan_primary_dev_id -> DRM_NODE_PRIMARY), so on hybrid/eGPU/muxless setups selecting a headless render GPU via --prefer-vk-device also forces scanout onto that GPU, which has no connectors -> black screen. --prefer-drm picks the KMS device explicitly while --prefer-vk-device keeps choosing the render GPU and -O selects the connector within it. Accepts /dev/dri/cardX, the short cardX form, and /dev/dri/by-path/...-card symlinks. Also read from $GAMESCOPE_PREFER_DRM when the flag is absent, so a session can configure a split setup without per-game options. The node is validated by device number (primary minors 0-63) up-front in main(), not by open() (which the compositor cannot do for a primary node under seatd/logind); drmIsKMS() still runs later. Default behavior is unchanged when neither is set. Also submitted upstream: ValveSoftware#2220.
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Carries the
--prefer-drmoption in the Bazzite gamescope fork so hybrid / eGPU / headless-render setups work in Game Mode.Problem:
init_drm()derives the KMS/scanout device from the selected Vulkan device (vulkan_primary_dev_id()→DRM_NODE_PRIMARY). So--prefer-vk-device(e.g. a headless render GPU) also forces scanout onto that GPU →'/dev/dri/cardX' is not a KMS device→ black screen, with no way to render on GPU A and scan out on display GPU B.Change: adds
--prefer-drm <device>to choose the DRM/KMS scanout device independently of--prefer-vk-device, plus aGAMESCOPE_PREFER_DRMenv fallback so the session can set it without per-game launch options. Accepts/dev/dri/cardX,cardX, and/dev/dri/by-path/…-card. Validated by device number up-front inmain()(notopen(), which the compositor can't do for a primary node under seatd/logind);drmIsKMS()still runs. No behaviour change without the flag/env.This pairs with Bazzite's
export-gpu(VULKAN_ADAPTER= render GPU): setGAMESCOPE_PREFER_DRMto the display GPU's by-path and the UI/games render on the fast GPU while output goes through the iGPU.Tested on Bazzite + CachyOS Game Mode (Intel iGPU + AMD BC-160): compositor on BC-160, scanout via Intel HDMI; Steam Big Picture and Cyberpunk 2077 work, no atomic/dmabuf errors.
Also submitted upstream: ValveSoftware#2220 (this carries it for Bazzite until it lands upstream). Upstream request: ValveSoftware#1004.