[U-Boot] Info on NAND-SPL

Hello,   I was trying to understand how NAND-SPL works. What I could understand after seeing the code is that 1) NAND-SPL is a standalone application which will load the U-boot in the main memory. 2) After doing the clock and DRAM initialization it will relocate itself in the DRAM. 3) Then it will copy the u-boot from the nand into the RAM and execute the u-boot.   If my understanding is proper, then I have one doubt 1) Since the nand_spl is making use of the same Start.S and lowlevel_init.S, the u-boot code will also perform relocation? So is it not a overhead doing relocation twice?   Also is there any similar implementation for MMC-SPL?   Thanks Hatim