3. Privileged or Secure Firmware

3.1. AArch32 Multiprocessor Startup Protocol

There is no standard multiprocessor startup or CPU power management mechanism for ARMv7 and earlier platforms. The OS is expected to use platform specific drivers for CPU power management. Firmware must advertize the CPU power management mechanism in the Devicetree system description or the ACPI tables so that the OS can enable the correct driver. At ExitBootServices() time, all secondary CPUs must be parked or powered off.

3.2. AArch64 Multiprocessor Startup Protocol

On AArch64 platforms, Firmware resident in Trustzone EL3 must implement and conform to the Power State Coordination Interface specification [PSCI].

Platforms without EL3 must implement one of:

• PSCI at EL2 (leaving only EL1 available to an operating system)

• Linux AArch64 spin tables [LINUXA64BOOT] (Devicetree only)

However, the spin table protocol is strongly discouraged. Future versions of this specification will only allow PSCI, and PSCI should be implemented in all new designs.