CPU_METHOD_OF_DECLARE() with Linux as non-secure OS

[Mason]

Hello,

I'm working on a dual-core SoC (Cortex-A9 MPCore) with Linux running
as the non-secure OS. The secure OS implements some of the APIs used
in OMAP2 via SMC.

To start the second core, I used to define .smp in my DT_MACHINE_START
definition, but Arnd wrote: "There are other ways to do [.smp and .restart]
too, see CPU_METHOD_OF_DECLARE() and register_restart_handler()."

Is CPU_METHOD_OF_DECLARE() the way to go?
Is it "compatible" with executing smc to ask the secure OS to do whatever
is needed to start the second core? (I don't understand why starting cores
is secure OS responsibility.)

I've located three relevant secure OS services:
get_aux_core_boot
set_aux_core_boot0
set_aux_core_boot_addr

I'm looking for guidance. What mach-* should I take as a reference to
implement "second core startup from non-secure OS"?

An ARM engineer suggested PSCI a while back, but I can't change the
secure OS API at this time.

Regards.