I have connected an MXI Express cable to a USRP X310 at one end and to my system at the other end. I successfully installed the RIO drivers on my system. Below are the logs for the issue I encountered.
wire@oai:~$ lspci -k -d 1093:c4c4
06:10.0 Signal processing controller: National Instruments PXIe/PCIe Device
Subsystem: National Instruments PXIe/PCIe Device
Kernel modules: niusrpriok
wire@oai:~$ uhd_find_devices
[INFO] [UHD] linux; GNU C++ version 9.4.0; Boost_107100; UHD_4.6.0.HEAD-0-g50fa3baa
No UHD Devices Found
wire@oai:~$ uhd_usrp_probe --args="resource=RIO0"
[INFO] [UHD] linux; GNU C++ version 9.4.0; Boost_107100; UHD_4.6.0.HEAD-0-g50fa3baa
[ERROR] [UHD] Device discovery error: RuntimeError: x300::pcie_manager::find: Error enumerating NI-RIO devices. Unknown error. (Error code -52012)
Error: LookupError: KeyError: No devices found for ----->
Device Address:
resource: RIO0
wire@oai:~$ lspci | grep "National"
06:10.0 Signal processing controller: National Instruments PXIe/PCIe Device