At our work company, we recently made the design of a new board using a KSZ9031 for ethernet connection.
It is working OK in 10/100 mbits mode : I can ping an other host without any issue.
The problem appears when trying gigabit connection : the interface goes up and then down a few seconds later, like a yoyo.
I tried using the mi-tool utility to dump phy registers, but I'm getting an error : SIOCGMIIPHY on 'eth0' failed: No such device.
So the question is : what could be the issue if phy is working in 100mbits but not gigabit ?
We are using a kernel 3.10.17 and I implemented the device tree to support the phy.
I have no experience debugging ethernet phy hardware issues so any help / hint is appreciated.