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

=== Assistant: Got it — thanks, that helps a lot. ===
Got it — thanks, that helps a lot.
Based on what you’re seeing, here’s the key conclusion first, then the fix path.

==== - ✅ Desktop Mode ====
* ✅ lspci does see the 9070 XT
* ❌ HDMI on the eGPU is not detected at all
* ❌ xrandr commands don’t bring it back
* ❌ After reboot it “looks like the eGPU isn’t recognised” from a display point of view

This means:

: 

So this is not Thunderbolt, not BIOS, not cabling.
It’s a kernel/Mesa regression in SteamOS affecting AMD eGPU display outputs.

This lines up exactly with recent SteamOS behavior.

==== Previously: ====
* Kernel initialized the eGPU early enough
* DRM/KMS enabled HDMI during boot
* Desktop manager saw the output

After an update:
* iGPU claims primary DRM master
* eGPU becomes “render-only”
* Its HDMI never gets modeset

That’s why:
* GPU shows up
* But TV stays black forever

==== ### ====

Even if you think you’re on X11, make sure.
# Desktop Mode → Log out
# On login screen: - Click ⚙️ - Select Plasma (X11)
# Log in

Now edit kernel params:

<syntaxhighlight lang="bash">sudo steamos-readonly disable
sudo nano /etc/default/grub

</syntaxhighlight>

Find:

<syntaxhighlight>GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

</syntaxhighlight>

Change to:

<syntaxhighlight>GRUB_CMDLINE_LINUX_DEFAULT="quiet splash amdgpu.dc=1 amdgpu.dpm=1"

</syntaxhighlight>

Then:

<syntaxhighlight lang="bash">sudo update-grub
sudo steamos-readonly enable
sudo reboot

</syntaxhighlight>

Boot with eGPU + HDMI already connected.

===== Create a modprobe override: =====

<syntaxhighlight lang="bash">sudo steamos-readonly disable
sudo nano /etc/modprobe.d/amdgpu-egpu.conf

</syntaxhighlight>

Add:

<syntaxhighlight>options amdgpu dc=1

</syntaxhighlight>

Save, then:

<syntaxhighlight lang="bash">sudo steamos-readonly enable
sudo reboot

</syntaxhighlight>

This forces the display core to initialize outputs.

===== After reboot (even if TV is black): =====

<syntaxhighlight lang="bash">ls /sys/class/drm/

</syntaxhighlight>

You should see something like:
* card1-HDMI-A-1

If no HDMI entries exist for card1, the bug is 100% driver-side.

==== If you need the TV now: ====
* Boot without HDMI
* Log into Desktop Mode
* Plug HDMI in after login
* Sometimes xrandr will then see it

Not great, but functional.

==== This is a known SteamOS regression: ====
* AMD RDNA3 eGPUs
* External displays
* After recent kernel/Mesa updates

You didn’t break anything.

==== Just answer these and I’ll give you the final best path (including rollback if needed): ====
# What SteamOS branch and version are you on?
# Output of: ``<code>bash ls /sys/class/drm/ </code>``

We’re past guessing now — this is a driver initialization issue, and you’re very close to a stable workaround.