Building U-Boot and Linux Kernel for Toradex Colibri iMX6ULL SoM

I sometimes find Toradex documentation hard to google and browser, hence this quick note which has all the essentials in one go!

1. kernel tree: imx6ull colibiri is very well supported upstream. for everything 5.x kernels just use mainline
2. uboot tree: I use the toradex uboot released here https://git.toradex.com/cgit/u-boot-toradex.git/ (tested tag toradex_2020.07)
3. uboot defconfig: use colibri-imx6ull_defconfig
4. linux defconfig: use imx6_imx7_defconfig; maybe add your own fragments with kernel scripts/merge-config.sh
5. device tree: the dtb to use for a standard colibri imx6ull with 256M of RAM is: imx6ull-colibri-eval-v3.dtb; for the wifi/bluetooth edition use: imx6ull-colibri-wifi-eval-v3.dtb
6. toolchain: any modern cross toolchain worked well for me. I used musl and glibc linaro toolchain for armhf for the time being, e.g. good binary musl cross toolchains are available from https://musl.cc/
7. format: Toradex uboot default configuration is happily booting zImage, but not uImage, so go for the former.

Give it a try!