m920q-pcie-bifurcation

Lenovo M920Q and M720Q PCIe x8 bifuration to x4x4 hardware mod by soldering missing components to the board.

PCIe x8 bifurcation mod to x4x4

It looks like this might work, placeholder, WIP.
Referring to post on STH, M720Q/M920Q models have the x8 PCI-E slot directly wired to the CPU.
Looking at soldered SMD components and board schematics, I see board is in CFG[6:5]:1:0" configuration, which is "10 = 2 x8 PCI Express" mode. This makes sense, we have lines 0-7 in slot available. Goal would be to make "CFG[6:5]:0:0" configuration which will give "00 = 1 x8, 2 x4 PCI Express" mode.



After that, need to reverse PCIe lines (0-7 --> 7-0) with CFG[2]:0 configuration which should give us x4x4 lanes. This looks too easy to be true, need some testing...

Testing

Does not work with Supermicro AOC-SLG3-2M2. Now ordered this x8 adapter for further testing https://www.amazon.de/dp/B09MSB4TXT

Components location on the board

placeholder, wip