[U-Boot] ARM64: How to protect spin-table code from U-Boot?

[Masahiro Yamada]

Hi.

I assume the following code in
arch/arm/cpu/armv8/start.S is for spin-table.



#ifdef CONFIG_ARMV8_MULTIENTRY
       branch_if_master x0, x1, master_cpu

       /*
        * Slave CPUs
        */
slave_cpu:
       wfe
       ldr x1, =CPU_RELEASE_ADDR
       ldr x0, [x1]
       cbz x0, slave_cpu
       br x0 /* branch to the given address */
master_cpu:
       /* On the master CPU */
#endif /* CONFIG_ARMV8_MULTIENTRY */



As Documentation/arm64/booting.txt of Linux says,
slave CPUs should spin outside of the kernel in a
reserved area of memory.

U-Boot generally works on DRAM, so the code for spin-table
should be reserved in Device Tree.

Otherwise, the code above and the variable "CPU_RELEASE_ADDR"
has been destroyed by the kernel by the time slave CPUs are kicked.

Now, I locally work-around this problem by pre-fetching necessary code
to the I-cache, but this solution is unstable.


My question is, is there a solution to protect spin-table code already?
(or on-going work to solve the problem?)

One problem specific for U-Boot is that,
U-Boot relocates itself to the tail of DRAM.
So, it is difficult to reserve the code statically at the compile time of DT.


Thought?


-- 
Best Regards
Masahiro Yamada