I admit this is not well documented anywhere on our developer website so far.
First you would need to stop X from being started upon boot as the Tegra X driver has issues if launched without any display interface being active:
root@colibri-t30:~# systemctl disable lxdm
Removed symlink /etc/systemd/system/display-manager.service.
Then upon rebooting simply enter the U-Boot boot loader’s command shell console and disable the display interfaces as follows:
Colibri T30 # setenv vidargs 'video=tegrafb0:off video=tegrafb1:off'
Colibri T30 # saveenv
Saving Environment to MMC...
Writing to MMC(0)... done
As for Ethernet this is realised by an ASIX AX88772B USB-to-Ethernet chip on the module whose reset and VBUS lines are controlled by the following GPIO’s:
root@colibri-t30:~# cat /sys/kernel/debug/gpio | grep LAN_
gpio-232 (LAN_RESET ) out hi
gpio-234 (LAN_V_BUS ) out hi
One can simply keep the Ethernet chip in reset and deassert VBUS to completely turn it off as follows:
root@colibri-t30:~# echo 0 > /sys/class/gpio/gpio232/value
[ 230.272092] usb 1-1: USB disconnect, device number 2
[ 230.279574] eth0: unregister 'asix' usb-tegra-ehci.1-1, ASIX AX88772B USB 2.0 Ethernet
[ 230.405699] ADDRCONF(NETDEV_UP): dummy0: link is not ready
[ 230.412952] ADDRCONF(NETDEV_UP): sit0: link is not ready
[ 230.418276] ADDRCONF(NETDEV_UP): ip6tnl0: link is not ready
root@colibri-t30:~# echo 0 > /sys/class/gpio/gpio234/value