use firefly firmware to make sure the hardware is OK
and 3566-pc using gmac1 m0 group pins, and this group of pins is multiplexed with uart3 m1 group
maybe you enabled uart3 m1 and it conflicts with gmac1, you need to config uart3 to use m0 in dts
BUT, uart3 m0 is multiplexed with i2c3 m0, so to use uart3, you need to disable i2c3
