This is a really weird struggle: I have 2x cubieboard that are exactly identical (same HW, same board revision) including the LAN chip (realtek RTL8201CP). Both boards work fine with an earlier version of Armbian. I learned that there is an (unsupported) Armbian 21.08.1 Bullseye with Linux 5.15.25-sunxi which I installed on both. Behavior however differs with the LAN (eth0) interface. The one board works straight from install with DHCP (default), the 2nd won't work at all.
dmesg | grep eth (partially) outputs:
sun7i-dwmac 1c50000.ethernet eth0: no phy at addr -1
sun7i-dwmac 1c50000.ethernet eth0: stmmac_open: Cannot attach to PHY (error: -19)
nmcli outputs:
eth0: disconnected
"eth0"
1 connection available
ethernet (sun7i-dwmac), 02:50:08:01:72:49, hw, mtu 1500
I am certain that a proper connection is available, putting in a different sdcard with alternative (old) version of armbian runs fine with LAN. Bullseye is desired because of proper SUNXI audio codec implementation (capture side / line in).
There is no background I can figure for the differences, I will be very happy to receive suggestions what I could do to handle this.