The following error occurs when driving two MMCMs from a single port.
ERROR: [Place 30-716] Sub-optimal placement for a global clock-capable IO pin-BUFGCE-MMCM pair. If this sub optimal condition is acceptable for this design, you may use the CLOCK_DEDICATED_ROUTE constraint in the .xdc file to demote this message to a WARNING. However, the use of this override is highly discouraged. These examples can be used directly in the .xdc file to override this clock rule.
< set_property CLOCK_DEDICATED_ROUTE BACKBONE [get_nets port_clocking_inst/lopt] >
port_clocking_inst/BUFGCE (BUFGCE.O) is provisionally placed by clockplacer on BUFGCE_X0Y168 (in SLR 1)
port_clocking_inst/sys_mmcm0_inst/inst/mmcme3_adv_inst (MMCME3_ADV.CLKIN1) is provisionally placed by clockplacer on MMCME3_ADV_X0Y6 (in SLR 1)
port_clocking_inst/sys_mmcm1_inst/inst/mmcme3_adv_inst (MMCME3_ADV.CLKIN1) is provisionally placed by clockplacer on MMCME3_ADV_X0Y8 (in SLR 1)