toolchain mismatch between doc and Makefiles

[AnthoJack]

The SOO user guide recommends installing a "arm-linux-gnueabihf" toolchain but u-boot's Makefile expects a "arm-none-eabi" toolchain. linux uses the former when compiling

This results in an error at compile time for u-boot because the toolchain it uses doesn't recognize the architecture given in -mtune

[daniel-rossier]

I suggest to use the same toolchain (32-bit) than the other components (kernel, rootfs, etc.)