How can this code work out in Linux kernel?

Question

In linux kernel, in file arch/arm/mach-exynos/cpuidle.c, there is the following code:

    local_irq_disable();

    cpu_do_idle();

    local_irq_enable();

where cpu_do_idle is

    dsb         
    wfi
    mov     pc, lr

In cpu_do_idle, it does 'wfi' command which stands for wait for interrupt. But, what I'm not understanding is that it enters cpu_do_idle after disabling irq. How does this happen?

Answer 1

WFI waits for the hardware interrupt, regardless the current interrupt handling state of the CPU. When CPU is woken up, it has the chance to re-enable interrupts and process any pending ones:

WFI suspends execution until one of the following events occurs:

• an IRQ interrupt, regardless of the CPSR I-bit

• an FIQ interrupt, regardless of the CPSR F-bit

• an Imprecise Data abort, unless masked by the CPSR A-bit

• a Debug Entry request, regardless of whether Debug is enabled.

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0489c/CIHEGBBF.html