I decided to try U-Boot on the Raspberry Pi 2, and the process has been fairly well documented in several places..

I used the latest U-Boot, with ‘patch’ info from here, as I needed Device Tree support:  https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=108217.

Actual ‘installation’ is simple, as I just copied the u-boot binary to the boot directory on the SD Card, and edited config.txt to ‘boot’ U-Boot instead of the actual kernel, by changing kernel=kernel7.img to kernel=u-boot.bin.

On first boot, the uart/console output looked like this:

U-Boot 2015.07-rc3 (Jul 14 2015 - 13:49:19 -0700)

DRAM: 880 MiB
WARNING: Caches not enabled
RPI 2 Model B
MMC: bcm2835_sdhci: 0
reading uboot.env

** Unable to read "uboot.env" from mmc0:1 **
Using default environment

In: serial
Out: lcd
Err: lcd
Net: Net Initialization Skipped
No ethernet found.
Hit any key to stop autoboot: 0
U-Boot>

After this, I added definitions to set up the necessary boot parameters, etc.:

setenv machid 0x00000c42
setenv bootargs 'earlyprintk console=tty0 console=ttyAMA0,115200n8 root=/dev/mmcblk0p2 rootfstype=ext4 rootwait noinitrd'
setenv x_bootcmd_kernel fatload mmc 0:1 ${kernel_addr_r} zImage
setenv x_bootcmd_fdt fatload mmc 0:1 ${fdt_addr_r} bcm2709-rpi-2-b.dtb
setenv bootcmd '${x_bootcmd_kernel}; ${x_bootcmd_fdt}; bootz ${kernel_addr_r} - ${fdt_addr_r};'

saveenv (to save the parameter info to uboot.env on the SD Card)

Note that you do not need to explicitly state the kernel and device tree file load addresses, as – with the patch – these are already defined in the compiled U-Boot executable (as kernel_addr_r and fdt_addr_r respectively).
Of course, there are alternative ways of doing this, but this is a format I have used before with other devices..

I had been booting kernel7.img as an ‘uncompressed’ Image, but U-Boot expects zImage or uImage formats, so I changed my compile workflow on the Pi2 accordingly:

make -j5 zImage
make dtbs
make -j5 modules
make modules_install
make firmware_install
cp System.map /boot
cp arch/arm/boot/dts/bcm2709-rpi-2-b.dtb /boot
cp arch/arm/boot/zImage /boot

My next project will probably be to see if I can get U-Boot running on the ARM64 HiKey, but that might be a bit premature…

Robert Gadsdon.   July 15, 2015.