I am working on a carrier card design for the UltraZed-EV SOM and I need to create two Gen3 mini pci-e slots on it. Since mini pci-e is always a single lane, my thought is to simply make a 2-lane root complex bridge and run a lane to each slot. But I have no idea if link negotiation, etc. would work. I'm not sure if this is a legitimate methodology to simply split up the lanes, or if I would have to get fancier using something like a 2x2 crossbar switch or a full PCIe switch.
Generally speaking, the reference design information that is available has been quite useful in working through this, and has good info about a single PCIe port, but I'm unable to locate any set of schematics or information that detail more than one slot that I could use as a reference.