Hi all,
I spent the better half of the day finding out how to get my Mellanox ConnectX-3 MCX311A with latest firmware to be recognized in Windows 10 (also latest updates installed, incl. Intel Chipset Drivers. Mainbord is an Asus ROG Strix z390 Gaming-F, also with latest Bios. I have a RTX 3080 (which takes 16 PCI-E lanes from the CPU) and an M.2 NVME Samsung 970 EVO, which takes 4 lanes from the Chipset. Other than that, all peripherals except the USB ports and audio chipset are turned off in the Bios to save on PCI-E lanes. SATA ports completely disabled.
The GPU is in PCE-E x16 slot 1, slot 2 is vacant, slot 3 is housing the mellanox. I don't want any card near the GPU for thermal reasons and not sacrifice x8 lanes.
So in theory there should be enough lanes to spare for the Mellanox...but: It is not recognized properly in Win 10 with the well known error code 43, all the time with no exception.
The solution that seems to run stable is: Switch the PCI-E x16_3 slot from x4 lanes to x2 lanes. This seemed to eliminated the problem, and i verified with HWINFO that the settings in the BIOS have an effect on the actual lane usage of the Mellanox. I will continue testing and edit this post, if this really solved the issue long term.