Ethernet and SGMII both have an auto-negotiation process that are independent of each other. Ethernet auto-negotiation occurs between an Ethernet PHY and the PHY link partner over the MDI lines. During this process, the two devices exchange information about speed, duplex mode, and flow control and link up at the maximum capability advertised by both link partners.

SGMII auto-negotiation is a process where the PHY sends updated control information to the MAC. This control information is specified in the Cisco SGMII Standard. When the MAC receives this information, the MAC acknowledges reception of the updated control information by asserting an acknowledge bit. In TI Ethernet PHY, this acknowledge bit is associated with the register bit SGMII Page Received. In SGMII auto-negotiation, there is no maximization of capabilities, just information exchange between PHY and MAC.

If SGMII link-up issues occur, check that auto negotiation is either disabled in both PHY and MAC or enabled in both PHY and MAC. In either case, the PHY and MAC must support the same communication speeds.

If the PHY comes up before the MAC, a SGMII restart can be required for the MAC to receive control information for successful link up.

If SGMII link up is still unsuccessful, the auto-negotiation timer can also be adjusted for some TI Ethernet PHYs so that the entire auto negotiation cycle is slower or faster on the PHY side. To adjust the timer, set the sgmii_autoneg_timer bit field described in the device data sheet and then restart SGMII auto negotiation or reset the PHY by writing 0x1F=0x4000.