My Proxmox host is built around an ASRock X300M-STX with a Ryzen 5 PRO 5650G. It’s a neat little always-on box: small, quiet, and powerful enough for a handful of VMs and containers. The annoying part is that the most interesting power and virtualisation controls live in the BIOS, behind labels that are not always obvious.

ASRock supplied a P2.20B BIOS for this board with ACS/ARI behaviour enabled. That’s useful for Proxmox because PCIe devices land in cleaner IOMMU groups without needing pcie_acs_override. I wanted to keep that benefit, but also understand what the board was doing for idle power.

Pulling the BIOS apart

The useful path was:

  1. Extract the AMI UEFI image with UEFIExtract.
  2. Run ifrextractor against the right Setup, AMD CBS, AMD PBS, and AMD Overclocking modules.
  3. Search the IFR output for settings like C-state, CPPC, Power Supply Idle, ASPM, L1, IOMMU, ACS, and ARI.
  4. Compare the extracted offsets with live efivarfs values on the running Proxmox host.

The last step matters. A saved BIOS profile file is not the same thing as live UEFI variables. It can show that bytes changed, but it does not reliably tell you “this byte is AmdSetup offset 0x145”. Live read-back from /sys/firmware/efi/efivars/ is much more useful.

What was worth looking at

The obvious CPU-side settings were mostly already sane. Linux was using amd-pstate-epp, CPPC was effectively working, and CPU idle states were active. Changing BIOS values from Auto to Enabled would mostly be about determinism, not a guaranteed idle-power win.

The PCIe side was more interesting. The NVMe drives, Realtek LAN, and Intel AX200 endpoint all showed ASPM disabled. Some endpoints advertise L1 or L1 substates, but the platform/root-port side decides whether Linux can safely enable the link. That makes the BIOS PM L1 SS setting a good candidate for careful staged testing, not something to blindly force with pcie_aspm=force.

The other high-value candidates were more mundane:

  • Leave Bluetooth enabled, because I actually use it.
  • Potentially disable only Wi-Fi, since the AX200 exposes Wi-Fi over PCIe and Bluetooth over USB.
  • Disable unused HD audio on a headless server, but only after confirming the live variable path.
  • Treat ECO mode as a load-power cap, not an idle-power fix.

The useful surprise

The P2.20B BIOS did exactly what I needed for IOMMU grouping. Both NVMe drives, LAN, Wi-Fi, iGPU functions, USB controllers, and SATA all appeared in separate groups without kernel ACS override. That is the thing I would not want to break while chasing a watt or two.

The less useful surprise was that one expected Setup efivar was not exposed on the live host, and one Power Supply Idle Control offset read back as a value outside the IFR option list. That is exactly why I prefer a read-only collector and staged changes over writing NVRAM directly from a table of offsets.

Source and notes: aioue/asrock-x300m-stx-bios