Supermicro H12SSL-I & Modded 4090 issues

Hardware Hub
1

Supermicro H12SSL-I / EPYC 7702 hangs at POST code 94 (“DXE–BIOS PCI Bus Enumeration”) when a 48 GB VRAM-modded RTX 4090 is installed. System boots normally with the GPU removed. Same behavior on BIOS 3.1 and latest BIOS 3.7/BMC 1.08.03. Above 4G Decoding enabled; ReBAR tested both enabled and disabled; pure UEFI boot; onboard VGA primary. Card was installed in CPU SLOT7 PCIe 4.0 x16. Currently testing SLOT5 to see whether it’s root-port/slot-specific.

Checking post snooping it seems to hit b4 before the whole thing stops.

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Same here on H12SSL-CT / EPYC 7003: 8x multi-function GPU cards. Rock solid with 6 cards, hangs at POST 9C during DXE with any 7th card in any slot. Ruled out Above 4G, Re-BAR, SR-IOV, ARI, forced Gen1/Gen2 link speed, USB disabled, CSM, bifurcation, BIOS 3.3/3.7. Resource math is fine (~304M per card, 1.7G used of 224G window). Looks like an AMI DXE allocator defect beyond 6 Root Ports/endpoints.