We are also working on communication between Ethernet MAC to MAC without PHY.
In our case, it is iMX8 to iMX8 comm over MAC.
There are two modules in MAC, Transmit & Receive.
What i understand is, we can connect Tx module signals to the Rx module signals & vice versa.
MAC1_TxC --> MAC2_RxC
MAC1_Tx_CTL --> MAC2_Rx_CTL
MAC1_TxD[3:0] --> MAC2_RxD[3:0]
MAC1_RxC <-- MAC2_TxC
MAC1_Rx_CTL <-- MAC2_Tx_CTL
MAC1_RxD[3:0] <-- MAC2_TxD[3:0]
The clock config can be internal to the each MAC for TxC. Or can be tied up external clock to ENETx_REFCLK_125M_25M pin.
Let me know if you see any issue with the above connections.