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 for <linuxppc-dev@lists.ozlabs.org>; Thu, 24 Nov 2011 17:25:48 +1100 (EST)
Subject: Re: [PATCH 2/6] powerpc/time: Use clockevents_calc_mult_shift
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From: Kumar Gala <galak@kernel.crashing.org>
In-Reply-To: <20111124060847.198884481@samba.org>
Date: Thu, 24 Nov 2011 00:25:32 -0600
Message-Id: <B695AB74-08F7-46DE-A9E9-BC7475FA1F3F@kernel.crashing.org>
References: <20111124060716.362614789@samba.org>
 <20111124060847.198884481@samba.org>
To: Anton Blanchard <anton@samba.org>
Cc: paulus@samba.org, linuxppc-dev@lists.ozlabs.org, miltonm@bga.com,
 johnstul@us.ibm.com
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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.
>=20
> Signed-off-by: Anton Blanchard <anton@samba.org>
> ---
>=20
> Index: linux-build/arch/powerpc/kernel/time.c
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- 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 =3D {
>        .name           =3D "decrementer",
>        .rating         =3D 200,
> -       .shift          =3D 0,	/* To be filled in */
> -       .mult           =3D 0,	/* To be filled in */
>        .irq            =3D 0,
>        .set_next_event =3D decrementer_set_next_event,
>        .set_mode       =3D decrementer_set_mode,
> @@ -913,31 +911,6 @@ static void decrementer_set_mode(enum cl
> 		decrementer_set_next_event(DECREMENTER_MAX, dev);
> }
>=20
> -static inline uint64_t div_sc64(unsigned long ticks, unsigned long =
nsec,
> -				int shift)
> -{
> -	uint64_t tmp =3D ((uint64_t)ticks) << shift;
> -
> -	do_div(tmp, nsec);
> -	return tmp;
> -}
> -
> -static void __init setup_clockevent_multiplier(unsigned long hz)
> -{
> -	u64 mult, shift =3D 32;
> -
> -	while (1) {
> -		mult =3D div_sc64(hz, NSEC_PER_SEC, shift);
> -		if (mult && (mult >> 32UL) =3D=3D 0UL)
> -			break;
> -
> -		shift--;
> -	}
> -
> -	decrementer_clockevent.shift =3D shift;
> -	decrementer_clockevent.mult =3D mult;
> -}
> -
> static void register_decrementer_clockevent(int cpu)
> {
> 	struct clock_event_device *dec =3D &per_cpu(decrementers, =
cpu).event;
> @@ -955,7 +928,8 @@ static void __init init_decrementer_cloc
> {
> 	int cpu =3D smp_processor_id();
>=20
> -	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 =3D
> 		clockevent_delta2ns(DECREMENTER_MAX, =
&decrementer_clockevent);
> 	decrementer_clockevent.min_delta_ns =3D
>=20
>=20
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