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Re: [PATCH v2] MIPS: Don't overflow cevt-r4k.c calculations at high cloc

To: David Daney <ddaney@caviumnetworks.com>
Subject: Re: [PATCH v2] MIPS: Don't overflow cevt-r4k.c calculations at high clock rates.
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 19 May 2010 19:42:44 +0200 (CEST)
Cc: linux-mips@linux-mips.org, ralf@linux-mips.org
In-reply-to: <1274290853-16947-1-git-send-email-ddaney@caviumnetworks.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <1274290853-16947-1-git-send-email-ddaney@caviumnetworks.com>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Alpine 2.00 (LFD 1167 2008-08-23)
On Wed, 19 May 2010, David Daney wrote:

> The 'mult' element of struct clock_event_device must never be wider
> than 32-bits.  If it were, it would get truncated when used by
> clockevent_delta2ns() when this calls do_div().
> 
> We can meet this requirement by using clockevent_set_clock() to set
> the MULT and SHIFT values.
> 
> Signed-off-by: David Daney <ddaney@caviumnetworks.com>
> CC: Thomas Gleixner <tglx@linutronix.de>

Acked-by: Thomas Gleixner <tglx@linutronix.de>

> ---
>  arch/mips/kernel/cevt-r4k.c |    5 ++---
>  1 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/mips/kernel/cevt-r4k.c b/arch/mips/kernel/cevt-r4k.c
> index 0b2450c..2a4d50f 100644
> --- a/arch/mips/kernel/cevt-r4k.c
> +++ b/arch/mips/kernel/cevt-r4k.c
> @@ -163,7 +163,6 @@ int c0_compare_int_usable(void)
>  
>  int __cpuinit r4k_clockevent_init(void)
>  {
> -     uint64_t mips_freq = mips_hpt_frequency;
>       unsigned int cpu = smp_processor_id();
>       struct clock_event_device *cd;
>       unsigned int irq;
> @@ -188,9 +187,9 @@ int __cpuinit r4k_clockevent_init(void)
>       cd->name                = "MIPS";
>       cd->features            = CLOCK_EVT_FEAT_ONESHOT;
>  
> +     clockevent_set_clock(cd, mips_hpt_frequency);
> +
>       /* Calculate the min / max delta */
> -     cd->mult        = div_sc((unsigned long) mips_freq, NSEC_PER_SEC, 32);
> -     cd->shift               = 32;
>       cd->max_delta_ns        = clockevent_delta2ns(0x7fffffff, cd);
>       cd->min_delta_ns        = clockevent_delta2ns(0x300, cd);
>  
> -- 
> 1.6.6.1
> 

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