We have a design with am3358 and two AR8035，the two AR8035 PHY ID is 4 and 6, the schematic is shown below.
During the aging test of Ethernet, sometimes we found that the mdio bus read with error value 0xFFFB(IO error), once the error appears, it will persistently return 0xFFFB. in fact the AR8035 is still working(Because ifthe driver ignores the 0xFFFB value, it pings other device well, so we think ar8035 is still working).
The problem occurs only on chip which PHY ID is 4 ,while the other PHY don't .
We have measured the wave of MDIO_CLK and MDIO_DATA, they all have obvious overshoot as below:
The design of this project referred.
Figure 1. PHY ID is 4
Figure 2 PHY ID is 6
Figure 3. MDIO_CLK near PHY ID 4
Figure 4. MDIO_CLK near PHY ID 6
