For SMP, CPU needs "ldex&stex" instructions for atomic operations.
For abiv2 we couldn't use "trap 1" as user space bkpt in gdbserver, because abiv2 is 16/32bit instruction set and "trap 1" is 32bit. So we need a 16bit instruction as user space bkpt, and it will cause an illegal instruction exception. In kernel we parse the *regs->pc to determine whether to send SIGTRAP or not.
The implementation are not only used by TCM (Tightly-Coupled Meory) but also used by sram on SOC bus. It follow existed linux tcm software interface, so that old tcm application codes could be re-used directly.
Say Y here to allow turning CPUs off and on. CPUs can be controlled through /sys/devices/system/cpu/cpu1/hotplug/target. Say N if you want to disable CPU hotplug.