{"slug": "am4-motherboard-with-quad-r9700-s-behind-plx88096-rombar-woes", "title": "AM4 motherboard with quad R9700's behind plx88096 ROMBAR Woes", "summary": "A user on an AM4 X570-D4U-2L2T/BCM motherboard resolved missing PCIe BAR space that blocked four R9700 AI GPUs behind a PLX88096 switch by disabling Legacy CSM support in the BIOS, which also restored the onboard 10GbE controller. The fix left peer-to-peer (P2P) disabled in AMD-SMI topology inside the VM passed through all four devices, with the access table showing only self-links ENABLED between 0000:01:00.0 through 0000:04:00.0. The user had applied kernel arguments including pci=realloc=on, amd_iommu=on, iommu=pt and pcie_aspm=off before finding the CSM setting was the cause.", "body_md": "So i recently got my PLX88096 chip in the mail, and have used it to install 4 R9700 AI’s onto the system, however it seems my poor prosumer grade AM4 X570-D4U-2L2T/BCM motherboard has had enough of my shenanigans and just doesnt have the BAR space to deal with it\n\nMy onboard 10Gbe also stopped working, but i suspect this is just a side effect of the lack of BAR space\n\nI’ve added the Dmesg logs and my kernel opts\n\nPlease  obi-wan janitobi’s, you guys are my only hope:\n\nKernel Args:\n\nGRUB_CMDLINE_LINUX_DEFAULT=“quiet amd_iommu=on iommu=pt pcie_aspm=off amdgpu.ras_enable=0 pci=realloc=on amdgpu.runpm=0 amdgpu.gpu_recovery=1 pcie_acs_override=downstream,multifunction, default_hugepagesz=1G hugepagesz=1G hugepages=108 transparent_hugepage=always”\n\nDMESG: See attachment\n\n[dmesg.txt](https://forum.level1techs.com/uploads/short-url/cuEyL12crKwewszQIO6ydsM2IAr.txt) (46.6 KB)\n\nFor your viewing pleasure(or distaste, depending on tolerance):\n\n \n\n \nIt WORKS!!!, it was Legacy CSM support being enabled, i have a new problem now though, even though everything is now properly showing inside the VM P2P is still disabled in AMD-SMI topology:\n\nACCESS TABLE:\n\n0000:01:00.0 0000:02:00.0 0000:03:00.0 0000:04:00.0\n\n0000:01:00.0 ENABLED      DISABLED     DISABLED     DISABLED\n\n0000:02:00.0 DISABLED     ENABLED      DISABLED     DISABLED\n\n0000:03:00.0 DISABLED     DISABLED     ENABLED      DISABLED\n\n0000:04:00.0 DISABLED     DISABLED     DISABLED     ENABLED\n\nWEIGHT TABLE:\n\nthis is inside the VM that’s being passed through all these devices", "url": "https://wpnews.pro/news/am4-motherboard-with-quad-r9700-s-behind-plx88096-rombar-woes", "canonical_source": "https://forum.level1techs.com/t/am4-motherboard-with-quad-r9700s-behind-plx88096-rombar-woes/257456#post_2", "published_at": "2026-09-30 17:37:57+00:00", "updated_at": "2026-09-30 17:49:07.700192+00:00", "lang": "en", "topics": ["ai-infrastructure", "ai-chips"], "entities": ["PLX88096", "AMD R9700", "AMD X570", "X570-D4U-2L2T/BCM", "AMD-SMI", "AM4"], "also_reported_by": [], "alternates": {"html": "https://wpnews.pro/news/am4-motherboard-with-quad-r9700-s-behind-plx88096-rombar-woes", "markdown": "https://wpnews.pro/news/am4-motherboard-with-quad-r9700-s-behind-plx88096-rombar-woes.md", "text": "https://wpnews.pro/news/am4-motherboard-with-quad-r9700-s-behind-plx88096-rombar-woes.txt", "jsonld": "https://wpnews.pro/news/am4-motherboard-with-quad-r9700-s-behind-plx88096-rombar-woes.jsonld"}}