Hi Matevz,
Thank you for your answer. :-) I don't know if it is supported but it would be really nice to try it out. Could you test ubuntu MATE 15.04 on your T4240QDS, please?
You have to download the initrd.gz and you have to convert it to a uinitrd:
Download:
http://ports.ubuntu.com/ubuntu-ports/dists/vivid/main/installer-powerpc/current/images/powerpc64/net...
Convert:
mkimage -T ramdisk -C gzip -n 'ubuntu MATE 15.04' -d initrd.gz uinitrd
=> setenv bootargs "console=ttyS0,115200 root=/dev/ram rw"
=> fatload usb 0:1 1000000 your_uImage
=> fatload usb 0:1 5000000 uinitrd
=> fatload usb 0:1 2000000 your.dtb
=> bootm 1000000 5000000 2000000
There is a small problem with the Ubuntu initrd.gz. The installation process tries to access the directory within the ramdisk where the kernel modules should be stored for your own custom kernel. However, there is no need for the kernel modules themselves. Hence, it is enough, when installation fails due to an harddisk recognition error, to enter the installation shell and create a directory '/lib/modules/<name_and_version_of_the_linux_kernel>'. Afterwards, the installation process works fine.
Cheers,
Christian