u-boot for Opal-6 is based off the 2015.01 source release.  The primary purpose is to boot an Operating System, but there are a number of other useful tools in u-boot which enable board level debugging and configuration during development.

Ethernet

Opal-6 Development Kits have a MAC address programmed into the fuses.  u-boot uses this to set the ethaddr environment variable.

Use the dhcp command to get an IP address or add an ipaddr environment variable.  Other standard u-boot networking commands are supported.

USB Flash Drive

Data can be accessed on USB flash drives.  Use the usb start command to activate USB, then the fat commands can be used to access data.

USB Mass Storage

The MMC can be accessed via the USB function port.  

Use the ums mmc 1 to access the partition.

Display Support

u-boot supports HDMI and Freescale 10.1" LVDS panels on the LVDS0 port.

It will auto-detect which interface is used, and default to the LVDS if both are present.

The u-boot documentation includes details on setting up a splash screen if you need this feature.