How to enable Gigabit ethernet in u-boot on AM335x EVM ?

Initial versions of the EVM did not have 1G Phy's on them. In the u-boot source

board/ti/am335x/evm.c

The speed is initially set to 1G, but depending on the board type in the function board_eth_init the speed will be decreased. EVM boards that are 1.1A or greater have 1G Phys on them. Here is a snippet of the code that performs that speed downgrade based on board type.

        } else if (board_id == IA_BOARD) {

                cpsw_slaves[0].phy_id = 30;

                cpsw_slaves[1].phy_id = 0;

                /* No gigabit */

                cpsw_data.gigabit_en = 0;

        } else {

                /* set mii mode to rgmii in in device configure register */

                writel(RGMII_MODE_ENABLE, MAC_MII_SEL);

        }

        /* GP EVM 1.0 (A, B) does not have functional gigabit */

        if (board_id == GP_BOARD && !strncmp(header.version, "1.0", 3))

                cpsw_data.gigabit_en = 0;