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For the benefit of other users who may wish to use this board here is a few notes from my experience of getting Qubes R4.0 running:
Mobo: Asus KGPE-D16
CPU: AMD Opteron Processor 6282 SE
Memory: 4x MT36KSF2G72PZ-1G6E1FE
GPU: NVIDIA GeForce GT 710
Coreboot 4.11 (GRUB2)
As stated by other users, the onboard GPU is problematic with this motherboard and coreboot. I struggled to get the Qubes installer to accept the GT710 as the primary display. Thankfully the onboard GPU can be disabled either by disabling it when building coreboot or by physically setting a jumper on the motherboard (to which I chose the latter for easier debugging).
This however presents us with attempting to boot the installer headless-ly. I achieved this by having the installer on one USB stick and another with a grub.cfg on it which I could change on another machine when required. The grub.cfg inside coreboot’s ROM would chainload to this.
It should be noted that although this processor has IOMMU, and it was enabled in coreboot. Qubes installer warned that it was not present. This was overcome by appending ‘iommu=force’ to Xen’s command line.
With all this setup I was able to power the machine on, and my screen would turn on when Linux initialised via the second GPU (with the jumper set, to Linux this appeared to be the only GPU). The installer ran without issue.
Once installed, I removed the drive to inspect the generated grub.cfg file, and used the same method of chainloading config files to boot the system. Once I was satisfied with how the system was booting I embedded this into the ROM to remove the use of the USB stick. Creating symlinks to Xen, Linux and initrd helps in case of version updates, just remember to update them with any updates.
Without OpenBMC the fans run at full speed. sensors-detect with its default queries load a kernel module that incorrectly reports fan speed and cannot control them. However one of its questions does allow you to load a module that can control the fans (I’m not sure which one, I just ran ‘yes | sensors-detect’ to probe everything). With this done pwmconfig was able to quieten down the fans and saves having to buy the module.
Not KGPE-D16 specific however video performance was lacking with this card. However ‘sudo qubes-dom0-update kernel-latest’ helped this (a lot!, browser smooth scroll is smooth and YouTube plays decently).
SeaBIOS may have been easier than GRUB however I utilise GRUB’s signatures checks.
There is no audio ports on the rear panel and no headers (I think?). The manual recommends installing a sound card however audio through HDMI via the GPU works. If your screen speakers are crap like mine you can get HDMI audio video splitters.
The performance of this system is really great and much surpasses my former Qubes system (i7 X230). TPM modules are available which I'll invest in at some point. The performance looks to get better as NUMA awareness  is on the horizon (albeit with a ‘Far in the future’ milestone)
Heads  looks really hopeful and I’ll probably replace my current coreboot setup with it when I get a TPM. As Linux is the first thing that loads, I’m hopeful we can forget about all this VGA disabling annoyingness.
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