PCIe regression on Raspberry Pi Compute Module 4 breaks

Raspberry Pi 4 PCI-Express Bridge “Chip” raspberry pi 4 pcie slot Using the Raspberry Pi compute module, which includes a single PCI-e slot with a single PCIe lane and powering both the GPU and the Raspberry Pi raspberry pi 4 pcie slot Fast Compute Module 4 Powered by the powerful Raspberry Pi Compute Module 4 Expansion slot For NVMe SSDs ; socket M-Key; Supports 2230, 2242

raspberry pi slot machine It's got a mini PCI express slot, which I plan to use for a 4 port UART card I've got a card from Diamond systems which uses the EXAR XR17V354