AM79C901 HomePNA PHY is not thoroughly tested, there may be some bugs in the “on the fly” change of transceiver.

A bug is hidden somewhere in the receive buffer management code, the bug causes NULL pointer reference in the kernel. This fault is caught before bad things happen and reported with the message: eth0: NULL pointer encountered in Rx ring, skipping which can be viewed with dmesg or cat /var/log/message.

The media type change from 10Mbps to 100Mbps twisted-pair ethernet by ifconfig causes the media link down.