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The complexity of the boot sequence of UniPhier SoC family is
a PITA due to the following hardware limitations:

[1] No dedicated on-chip SRAM
SoCs in general have small SRAM, on which a tiny firmware or a boot
loader can run before SDRAM is initialized.  As UniPhier SoCs do not
have any dedicated SRAM accessible from CPUs, the locked outer cache
is used instead.  Due to the ARM specification, to have access to
the outer cache, the MMU must be enabled.  This is done for all CPU
cores by the program hard-wired in the boot ROM.  The boot ROM code
loads a small amount of program (this is usually SPL of U-Boot) from
a non-volatile device onto the locked outer cache, and the primary
CPU jumps to it.  The secondary CPUs stay in the boot ROM until they
are kicked by the primary CPU.

[2] CPUs can not directly jump to SDRAM address space
As mentioned above, the MMU is enable for all the CPUs with the page
table hard-wired in the boot ROM.  Unfortunately,...