u-boot/arch/x86/cpu/qemu/acpi/cpu-hotplug.asl

/* CPU hotplug */

Scope(\_SB) {
    /* Objects filled in by run-time generated SSDT */
    External(NTFY, MethodObj)
    External(CPON, PkgObj)

    /* Methods called by run-time generated SSDT Processor objects */
    Method(CPMA, 1, NotSerialized) {
	    /*
	     * _MAT method - create an madt apic buffer
	     * Arg0 = Processor ID = Local APIC ID
	     * Local0 = CPON flag for this cpu
	     */
        Store(DerefOf(Index(CPON, Arg0)), Local0)
        /* Local1 = Buffer (in madt apic form) to return */
        Store(Buffer(8) {0x00, 0x08, 0x00, 0x00, 0x00, 0, 0, 0}, Local1)
        /* Update the processor id, lapic id, and enable/disable status */
        Store(Arg0, Index(Local1, 2))
        Store(Arg0, Index(Local1, 3))
        Store(Local0, Index(Local1, 4))
        Return (Local1)
    }
    Method(CPST, 1, NotSerialized) {
	    /*
	     * _STA method - return ON status of cpu
	     * Arg0 = Processor ID = Local APIC ID
	     * Local0 = CPON flag for this cpu
	     */
        Store(DerefOf(Index(CPON, Arg0)), Local0)
        If (Local0) {
            Return (0xf)
        } Else {
            Return (0x0)
        }
    }
    Method(CPEJ, 2, NotSerialized) {
        /* _EJ0 method - eject callback */
        Sleep(200)
    }

    /* CPU hotplug notify method */
    OperationRegion(PRST, SystemIO, 0xaf00, 32)
    Field(PRST, ByteAcc, NoLock, Preserve) {
        PRS, 256
    }
    Method(PRSC, 0) {
        /* Local5 = active cpu bitmap */
        Store(PRS, Local5)
        /* Local2 = last read byte from bitmap */
        Store(Zero, Local2)
        /* Local0 = Processor ID / APIC ID iterator */
        Store(Zero, Local0)
        While (LLess(Local0, SizeOf(CPON))) {
            /* Local1 = CPON flag for this cpu */
            Store(DerefOf(Index(CPON, Local0)), Local1)
            If (And(Local0, 0x07)) {
                /* Shift down previously read bitmap byte */
                ShiftRight(Local2, 1, Local2)
            } Else {
                /* Read next byte from cpu bitmap */
                Store(DerefOf(Index(Local5, ShiftRight(Local0, 3))), Local2)
            }
            /* Local3 = active state for this cpu */
            Store(And(Local2, 1), Local3)

            If (LNotEqual(Local1, Local3)) {
                /* State change - update CPON with new state */
                Store(Local3, Index(CPON, Local0))
                /* Do CPU notify */
                If (LEqual(Local3, 1)) {
                    NTFY(Local0, 1)
                } Else {
                    NTFY(Local0, 3)
                }
            }
            Increment(Local0)
        }
    }
}