If the cfg_rcw_src configuration pins are set 0_0100_0000, the LS1020a PBL loads RCW of the LS1020a from SD/MMC. See the Table 4-9 of the LS1021a Reference Manual.
This configuration pins can be set using external pul-up/pull-down resistors.
If the LS1020a RCW bit 192-195 are set to 0110, the LS1020a PBL loads the LS1021a configuration for SD/MMC and provides boot from SD/MMC. See the Table 4-14 of the LS1020a Reference Manual.
NXP offers SDK 2.0-1703 Linux BSP. This BSP supports the TWR-LS1021a board. See documentation for this BSP:
https://www.nxp.com/docs/en/supporting-information/QORIQ-SDK-2.0-IC-REV0.pdf
NXP offers LSDK Linux BSP for ARM based Layerscape processors. See documentation for this BSP:
https://www.nxp.com/docs/en/supporting-information/LSDK-KC-REV18.03.pdf
These BSP supports generation the u-boot boot loader and Linux image for SD boot.
Have a great day,
Pavel Chubakov
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------