Update from original Marvell U-Boot to mainline U-Boot:
-------------------------------------------------------

Generate the U-Boot image with these commands:

$ make clearfog_defconfig
$ make

The resulting image including the SPL binary with the
full DDR setup is "u-boot-spl.kwb".

Now all you need to do is copy this image on a SD card.
For example with this command:

$ sudo dd if=u-boot-spl.kwb of=/dev/sdX bs=512 seek=1

Please use the correct device node for your setup instead
of "/dev/sdX" here!

Boot selection:
---------------

Before powering up the board, boot selection should be done via the SW1 dip
switch (0: OFF, 1: ON):

 - SPI:     00010
 - SD/eMMC: 00111
 - M.2 SSD: 11100
 - UART:    01001 [1]

[1]: According to SolidRun's manual, 11110 should be used for UART booting on
     the ClearFog 'Pro' variant.
     However, this doesn't work (anymore) at least on Rev. 2.1 (but '01001' as
     mentionend for the 'Base' variant does).

Boot from UART:
---------------

Connect the on-board micro-USB (CF Pro: CON11, CF Base: CON5)
to your host.

Set the SW1 DIP switches to UART boot (see above).

Run the following command to initiate U-Boot download:

  ./tools/kwboot -b u-boot-spl.kwb /dev/ttyUSBX

Use the correct UART device node for /dev/ttyUSBX.

When download finishes start your favorite terminal emulator
on /dev/ttyUSBX.