APIC / ACPI Build issue

Excuse my ignorance, I'm new to kernel development.

I've just patched my source with rc2-mm2 and there seems to be a build issue concerning APIC / ACPI support.

The error:

LD init/built-in.o
LD .tmp_vmlinux1
arch/i386/kernel/built-in.o(.text+0xdaca): In function `acpi_register_gsi':
: undefined reference to `mp_register_gsi'
make[1]: *** [.tmp_vmlinux1] Error 1

It seems that in arch/i386/kernel/acpi/boot.c
at line 462 we have:

#ifdef CONFIG_X86_IO_APIC
        if (acpi_irq_model == ACPI_IRQ_MODEL_IOAPIC) {
                mp_register_gsi(gsi, edge_level, active_high_low);
        }

#endif

...yet mp_register_gsi is only defined if:

(line 879 of arch/i386/kernel/mpparse.c)
#if defined(CONFIG_X86_IO_APIC) && defined(CONFIG_ACPI_INTERPRETER)

So if the .config looks like:

# Power management options (ACPI, APM)
#
# CONFIG_PM is not set

#
# ACPI (Advanced Configuration and Power Interface) Support #
# CONFIG_ACPI is not set
CONFIG_ACPI_BOOT=y

#
# CPU Frequency scaling

With the power management stuff turned off and SMP support enabled the result is this build error.

Does CONFIG_ACPI_INTERPRETER have to be defined? If so, then can we require the definition in arch/i386/kernel/acpi/boot.c as well? This is not an area I'm familiar with.

The last build I did was on 2.6.6-mm5 and things were okay there (same config).