REG_PORT_LINK_MD_CTRL
ret = ksz_pread8(dev, p, REG_PORT_LINK_MD_CTRL, &val1);
ret = ksz_prmw8(dev, port, REG_PORT_LINK_MD_CTRL, PORT_FORCE_LINK |
ksz_port_cfg(dev, p, REG_PORT_LINK_MD_CTRL, PORT_START_CABLE_DIAG, true);
ret = ksz_pread8(dev, port, REG_PORT_LINK_MD_CTRL, ®_val);