Thanks for the questions
For available information from the BSP UM, the section 4.1.3 introduced the methods to write the fip and the whole binary to the mmc.
For separate kenel, dts, and rootfs, there is no formal description from the UM, from my opinion, you may try it the following way.
- Firstly flash the whole pre-built images to MMC following the way introduced in the UM.
- Boot the board to the Linux via QSPI flash, then mount the mmc to the rootfs, there should be two partitions existed, copy your own kernel/dts to the partition 1.
- Clean the contents of partition2, copy your specific fsl-image-auto-s32xxxx.tar.gz(could be built from Yocto) to the partition 2, then extract it there, finally, you will get your own rootfs deployed.
- At last, boot the board via the MMC.
Hope it helps.
Best Regards
Chenyin