I have made a custom iMX28 board based on the mx28evk board using the SMSC LAN8720A Ethernet PHY and for a long time everything seemed to work as intended - at least until I started experience that the ethernet connection was unstable. The link is coming up for 1-2 seconds, then goes down again for a couple of second, comes up and so on... going on forever. Sometimes a reset helps, sometimes it doesn't. If the link comes up in the first try it stays up and the connection is rock stable.
I think I can rule out bad hardware because starting up with u-boot and downloading the kernel through TFTP works perfect every time. This never failed but as soon as Linux tries to start up the ethernet it fails again.
PHY registers are set to reasonable values, reset timing is correct, signals look fine... I compared how things are done in u-boot and Linux and see no differences concerning the phy setup.
I have struggled with this for several days now and I'm getting no where. Has anyone seen something similar? Or can somebody give me a hint on something to look for?
Help much appreciated,