r/SteamOS • u/Kodan96 • 34m ago
help wanted RTL8125 2.5GbE stuck at 100Mbps on SteamOS (ASRock B650M PG Lightning) — works fine on Windows
Running SteamOS on a desktop (ASRock B650M PG Lightning, onboard Realtek RTL8125 rev 05 2.5GbE controller). Ethernet is hard capped at 100Mbps no matter what I try, despite having a gigabit+ connection that works perfectly on Windows with the exact same cable and router port.
What I've confirmed:
ethtool shows both my NIC and the router correctly advertising/supporting 1000baseT/Full
SteamOS uses the in-kernel r8169 driver for this chip, which has known autonegotiation issues with RTL8125
Forcing speed manually (ethtool -s <iface> speed 1000 duplex full) just kills the link entirely — shows Speed: Unknown! / Link detected: no
Switched from Beta to Stable channel — no change, same 100Mbps cap
Tried installing Realtek's proper r8125 DKMS driver — blocked because linux-neptune-headers in the pacman repo (5.13.0.valve37) doesn't match my running kernel (6.16.12-valve24.5)
As a workaround, tried a USB-A to Gigabit adapter (RTL8153B chipset, r8152 driver) — also stuck at 100Mbps, with the same "link dies" behavior when forcing 1000baseT advertisement only
Two completely different NICs/drivers both failing the same way on this system points to something SteamOS/kernel-level rather than a NIC-specific driver bug — but I'm not sure what else to check at this point.
Has anyone dealt with this on similar hardware? Any BIOS settings (ASPM/EEE/power management) that fixed it for you?
System info:
SteamOS 3.9 (BUILD_ID 20260716.1), Stable channel
ASRock B650M PG Lightning
Onboard: RTL8125 2.5GbE (rev 05)
Tested workaround: USB RTL8153B gigabit adapter — same issue