As I see the HUSH shell is not enabled in the Multiplatform 2.0 u-boot. So it's not possible to do conditional scripting while booting. I tried to enbale the CONFIG_SYS_HUSH_PARSER in u-boot. Now conditional scripting is working but I'm not able to mount my UBI filesystem from kernel. The kernel does not find any ubi partition. If I'm using the u-boot without HUSH it's working again. The kernel commandline with the bootargs seems to be the same. So I guess it's because of interpreting some variables. The $(varname) is not working anymore. I had to substitude into $varname but there must be something else I do not find.
Thanks for any advice.