The enabling/disabling or Precoding is negotiated during link training. Whether Precoding is needed or not is largely dependent on the specific receiver implementation. As an example, receivers that rely heavily on DFE tap-1 may choose to request Precoding during link training. So, each receiver will make its own determination, based on the receiver architecture, as to whether it should request Precoding or not. Precoding is defined in the PCIe 5.0 specification but not in the PCIe 4.0 specification.