Quartus Prime 16.1: Cannot Edit PCIe BAR widths!!

I ran into this. The fix is that you need to go into Address Mapping and set the addresses first.

For example, for me bar[4] goes to two instances. In address mapping, I set the addresses as follows:

instance 1: 0x0000_0000_0000_0000-0x0000_0000_0000_001F

instance 2: 0x0000_0000_0000_8000-0x0000_0000_0000_801F

Then I went back into the HIP instantiation, and toggled between IO Bar and 64-bit prefetchable BAR. The 64-bit prefetchable BAR address width now changed from 5 to 16. (bit 15 is set in the address... it doubles the address space by setting bit 16).