The SerDes high speed "SerDes Receive Data" and "SerDes Transmit Data" ports work with 1000Base-X signals of SFP. So no PHY is needed between the SFP and the SGMII ports of the LS1021A. Please confirm.
Now if the same SFP cage is plugged in by a 100Base-FX SFP, can the high speed data lines from the SFP work with the SerDes port( SerDes Receive Data" and "SerDes Transmit Data") of the LS1021A? Is it necessary to place a PHY between the SFP and the SerDes ports of the LS1021A for this lower speed? If yes, please make recommendations.