You're not wrong, but PnP including the configuration basis for PCI which still sits at the config space layer of the latest and greatest PCIe. That's the piece

You're not wrong, but PnP including the configuration basis for PCI which still sits at the config space layer of the latest and greatest PCIe. That's the piece I find so significant. I work with GPUs that mostly communicate over a proprietary C2C connection, but how does the OS find them? PCI enumeration.