PCI GPU on PCIe-PCI riser only "activated" if no other GPU present

[8192K]

(Kind of a follow up to https://forum.proxmox.com/threads/a...3-virge-and-3dfx-voodoo-2-to-win98-vm.151048/, which I could solve by adding s3fb to the blacklist):

I have a system with 2 GPUs on PCIe (AMD Radeon WX4100 and Nvidia Geforce 3060) and I am currently trying to passthrough an old PCI GPU (S3 Virge) by the help of a PCIe 1x to PCI riser adapter. The system recognizes the PCI GPU just fine but there is no output on the attached screen. I cannot use it for GPU passthrough _unless_ I remove both PCIe GPUs.
Then Proxmox will show two lines on the PCI GPU on boot (but not the regular boot process) and I can passthrough the GPU to any VM.
What's the issue here?

 

[dcsapak]

since what you're doing is rather unusual (but cool nonetheless ) i can only speculate, but my guess would be that it has something to do with how graphics cards get initialized, and especially old ones.
bios + vga needs special steps in order to function correctly, and maybe the virtual bios (seabios) does something the gpu does not expect (or does not do something it would expect)

you could try to extract the rom in an initialized state and giving it to the vm to use, see https://pve.proxmox.com/wiki/PCI_Passthrough#The_'romfile'_option
but no promises there...

also it's possible that modern hardware does weird things with such an old graphics card since it's not really expected...

do you boot your physical host with uefi or bios(csm) boot?

 

[8192K]

Ok, I'll give the ROM file a try. I am booting using UEFI.

 

[8192K]

Did not have any effects. I'll stop pursuing this and build a 2000s PC instead.

 

[dcsapak]

Did not have any effects. I'll stop pursuing this and build a 2000s PC instead.

did you try booting your host with csm/bios instead of uefi ? but changing the setup is also understandable if using virtualization is too much of a hassle..