From WANDBOARD.ORG I got the board support package,
then built u-boot, kernel and root file system,
put it on a SD card, inserted it and the wb dual worked so far.
That encouraged me to download the latest stable linux kernel (4.5.2) and try to proceed like before.
To build the kernel I've used the defconfig from the bsp.
After figuring out that the newer kernel supports device tree, I additionally built the dtb for the wb dual.
Booting the new kernel with dtb and the same parameters as before doesn't show any problems,
but there is there is no framebuffer in /dev and no output on hdmi anymore.
Reviewing the kernel configuration I found a lot off i.MX6 framebuffer stuff in the kernel of the bsp.
Is the framebuffer in the newer kernel handled different? Does the kernel need different boot parameters?
Or do I have to move all these i.MX6 framebuffer things into the new kernel? And if yes, what is the best way to do this?
Linux development is new to me, so maybe some of my questions don't make sense.