We have a custom LS1046A board at which we have only connected D M/P wires from the second USB controller.
We do not get any USB device to register in U-Boot. Do you have any hints on what do change in U-Boot/DTB/Linux to get it working?
I have seen a suggestion to set Global hardware parameters register 3 (GHWPARAMS3) DWC_USB3_SS_PHY_INTERFACE to zero to "put" it in USB 2.0 mode. But this is a read only register and it is set to 1 (PIPE3/USB 3.0).