Re: [PATCH 08/24] C6X: process management

Arnd Bergmann
2011-08-22T20:56:26Z

On Monday 22 August 2011 16:09:29 Mark Salter wrote:

> diff --git a/arch/c6x/kernel/process.c b/arch/c6x/kernel/process.c
> new file mode 100644
> index 0000000..d7bc66f
> --- /dev/null
> +++ b/arch/c6x/kernel/process.c
>
> +/* hooks for board specific support */
> +void (*c6x_restart)(void);
> +void (*c6x_halt)(void);
> +void (*c6x_power_off)(void);
> +
> +/*
> + * power off function, if any
> + */
> +void (*pm_power_off)(void);
> +EXPORT_SYMBOL(pm_power_off);
> +
> +/*
> + * power management idle function, if any..
> + */
> +void (*pm_idle)(void);
> +EXPORT_SYMBOL(pm_idle);

You probably don't want two levels of indirection for the power_off
callback, so just reassign pm_power_off from a driver when needed.

> +static void default_idle(void)
> +{
> + asm volatile ("IDLE\n");
> +}
> +
> +/*
> + * The idle loop for C64x
> + */
> +void cpu_idle(void)
> +{
> + /* endless idle loop with no priority at all */
> + while (1) {
> + tick_nohz_stop_sched_tick(1);
> + while (!need_resched()) {
> + void (*idle)(void);
> +
> + smp_rmb();
> + idle = pm_idle;
> + if (!idle)
> + idle = default_idle;
> + idle();
> + }
> + tick_nohz_restart_sched_tick();
> +
> + preempt_enable_no_resched();
> + schedule();
> + preempt_disable();
> + }
> +}

Hmm, I'm having a small deja-vue here. I think I just commented on the same
bug in the hexagon architecture patches ;-)

You need to disable all interrupts before checking need_resched() and keep
them disabled until returning from the idle function. Otherwise you might
not wake up (or wake up late) after an interrupt handler has set
need_resched() and waits for interrupts to process while you have entered
the idle call.

Arnd