[PATCH 2/6] powerpc/time: Use clockevents_calc_mult_shift

[Kumar Gala]

On Nov 24, 2011, at 12:07 AM, Anton Blanchard wrote:

> We can use clockevents_calc_mult_shift instead of doing all
> the work ourselves.
> 
> Signed-off-by: Anton Blanchard <anton at samba.org>
> ---
> 
> Index: linux-build/arch/powerpc/kernel/time.c
> ===================================================================
> --- linux-build.orig/arch/powerpc/kernel/time.c	2011-11-17 10:11:49.035001617 +1100
> +++ linux-build/arch/powerpc/kernel/time.c	2011-11-17 10:11:51.175038860 +1100
> @@ -112,8 +112,6 @@ static void decrementer_set_mode(enum cl
> static struct clock_event_device decrementer_clockevent = {
>        .name           = "decrementer",
>        .rating         = 200,
> -       .shift          = 0,	/* To be filled in */
> -       .mult           = 0,	/* To be filled in */
>        .irq            = 0,
>        .set_next_event = decrementer_set_next_event,
>        .set_mode       = decrementer_set_mode,
> @@ -913,31 +911,6 @@ static void decrementer_set_mode(enum cl
> 		decrementer_set_next_event(DECREMENTER_MAX, dev);
> }
> 
> -static inline uint64_t div_sc64(unsigned long ticks, unsigned long nsec,
> -				int shift)
> -{
> -	uint64_t tmp = ((uint64_t)ticks) << shift;
> -
> -	do_div(tmp, nsec);
> -	return tmp;
> -}
> -
> -static void __init setup_clockevent_multiplier(unsigned long hz)
> -{
> -	u64 mult, shift = 32;
> -
> -	while (1) {
> -		mult = div_sc64(hz, NSEC_PER_SEC, shift);
> -		if (mult && (mult >> 32UL) == 0UL)
> -			break;
> -
> -		shift--;
> -	}
> -
> -	decrementer_clockevent.shift = shift;
> -	decrementer_clockevent.mult = mult;
> -}
> -
> static void register_decrementer_clockevent(int cpu)
> {
> 	struct clock_event_device *dec = &per_cpu(decrementers, cpu).event;
> @@ -955,7 +928,8 @@ static void __init init_decrementer_cloc
> {
> 	int cpu = smp_processor_id();
> 
> -	setup_clockevent_multiplier(ppc_tb_freq);
> +	clockevents_calc_mult_shift(&decrementer_clockevent, ppc_tb_freq, 4);
> +

Where's this magic 4 come from?

> 	decrementer_clockevent.max_delta_ns =
> 		clockevent_delta2ns(DECREMENTER_MAX, &decrementer_clockevent);
> 	decrementer_clockevent.min_delta_ns =
> 
> 
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