Hi, I was tackling the same error as you were with NixOS. You must apply some patches (pkgs/patches/linux-5.15-mvebu-pci-improvements.patch · ae71f8b49eeaa43a7555ab034970dfb2b655153b · Karel Kočí / NixTurris · GitLab), but even with that, it won’t work. I ended up discovering that you also have to disable CONFIG_PCIEASPM symbol (pkgs/default.nix · ae71f8b49eeaa43a7555ab034970dfb2b655153b · Karel Kočí / NixTurris · GitLab).
I also managed to get it working with Linux 6.0 (see the patches and config here: pkgs/default.nix · master · Karel Kočí / NixTurris · GitLab).