The JESD204C 8B10B core operates using a 32-bit (4-byte) datapath. The core clock frequency is always the line rate divided by 40. For example, for a serial line rate of 12.5 Gbps, the core clock frequency is 312.5 MHz.
The AXI4-Stream RX and TX Data interfaces operate at this core clock frequency. TX and RX core clock should be used as the clock source for these interfaces.