Editing Openai/69492970-fd84-8012-81ad-fad51507b9fe (section)

=== Assistant: Short answer first so you don’t chase ghosts: ===
Short answer first (so you don’t chase ghosts):

You can’t.
On the Lenovo Legion Go / Go S, the BIOS does not provide any option to prioritize a discrete GPU (including an eGPU) over the Z1 Extreme iGPU.

And on SteamOS/Linux, it wouldn’t help even if it existed.

Now let me explain why, and what you can actually do instead.

==== ### ====

The Legion Go S is designed like this:
* Internal screen → Z1 Extreme iGPU only
* No MUX switch
* No dGPU lane routing

So even if an eGPU is connected:
* The iGPU must initialize first
* The system cannot POST without it
* BIOS-level “dGPU first” is impossible

This is very different from gaming laptops that have:
* A dGPU on the motherboard
* A hardware MUX switch

The Legion Go simply doesn’t have that hardware.

===== BIOS options like: =====
* “Primary Display”
* “Discrete graphics first”

only apply to:
* GPUs soldered to the motherboard
* PCIe devices present during POST

Thunderbolt eGPUs:
* Initialize after BIOS handoff
* Are handled by the OS, not firmware
* Cannot be selected as “primary” in BIOS

So there is no hidden setting you’re missing.

==== Since BIOS control isn’t possible, you control GPU usage at the OS and application level. ====

===== SteamOS uses Vulkan/DRI device selection. =====

You can force a game to use the eGPU by setting launch options:

<syntaxhighlight lang="bash">DRI_PRIME=1 %command%

</syntaxhighlight>

If you have more than one external GPU:

<syntaxhighlight lang="bash">DRI_PRIME=pci-0000_XX_00_0 %command%

</syntaxhighlight>

You can check available devices with:

<syntaxhighlight lang="bash">ls /dev/dri/

</syntaxhighlight>

===== Even though the display is driven by the iGPU: =====
* Rendering can happen on the eGPU
* Frames are copied back over PCIe/TB

This is expected behavior and works fine for gaming.

You can confirm the active GPU in-game with:
* Mangohud
* vulkaninfo

===== In Desktop Mode: =====
* System Settings → Display and Monitor → Compositor
* Keep iGPU as display controller
* Let apps choose render device

SteamOS does not support a global “use eGPU for everything” toggle.

==== Save yourself hours: ====
* ❌ Hidden BIOS menus
* ❌ Lenovo BIOS mods
* ❌ GRUB “set primary GPU” hacks
* ❌ Disabling the iGPU (will black-screen)

None of these work on this device.

==== This is what actually gives stable results: ====
* Stable SteamOS branch
* Cold boot with eGPU connected
* iGPU handles display
* eGPU handles rendering (DRI_PRIME=1)
* No suspend / resume with eGPU attached

==== - Identify your exact eGPU device path for DRI_PRIME ====
* Set up Mangohud to confirm GPU usage
* Create per-game Steam launch presets
* Automate PCI rescan on boot

Just tell me 👍