The LS1012a supports only QSPI as source for RCW and PBL. See the Section 4.4.4.1 and bits 192-195 of the RCW in the LS1012a Reference Manual:
https://www.nxp.com/docs/en/reference-manual/LS1012ARM.pdf
Linux BSP supports only QSPI for u-boot source on the LS1012a board.
Have a great day,
Pavel Chubakov
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