Re: [PATCH] x86: clean up hpet timer reinit

From: Daniel Forrest
Date: Fri Feb 06 2009 - 11:07:14 EST


On Fri, Feb 06, 2009 at 03:09:43PM +0100, Ingo Molnar wrote:
>
> * Pavel Emelyanov <xemul@xxxxxxxxxx> wrote:
>
> > Sorry for late response - took some time to re-check this...
>
> Applied to tip:timers/urgent, thanks Pavel!
>
> Note, since i've already queued up the minimal fix i've created a delta
> cleanup patch from your v2 patch - see it below. (It is the exact same end
> result in terms of code, just a nicer splitup.)
>
> Ingo
>
> ------------------->
> >From ff08f76d738d0ec0f334b187f61e160caa321d54 Mon Sep 17 00:00:00 2001
> From: Pavel Emelyanov <xemul@xxxxxxxxxx>
> Date: Wed, 4 Feb 2009 13:40:31 +0300
> Subject: [PATCH] x86: clean up hpet timer reinit
>
> Implement Linus's suggestion: introduce the hpet_cnt_ahead()
> helper function to compare hpet time values - like other
> wrapping counter comparisons are abstracted away elsewhere.
> (jiffies, ktime_t, etc.)
>
> Reported-by: Kirill Korotaev <dev@xxxxxxxxxx>
> Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxx>
> Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
> ---
> arch/x86/kernel/hpet.c | 12 ++++++++++--
> 1 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
> index c761f91..388254f 100644
> --- a/arch/x86/kernel/hpet.c
> +++ b/arch/x86/kernel/hpet.c
> @@ -897,7 +897,7 @@ static unsigned long hpet_rtc_flags;
> static int hpet_prev_update_sec;
> static struct rtc_time hpet_alarm_time;
> static unsigned long hpet_pie_count;
> -static unsigned long hpet_t1_cmp;
> +static u32 hpet_t1_cmp;
> static unsigned long hpet_default_delta;
> static unsigned long hpet_pie_delta;
> static unsigned long hpet_pie_limit;
> @@ -905,6 +905,14 @@ static unsigned long hpet_pie_limit;
> static rtc_irq_handler irq_handler;
>
> /*
> + * Check that the hpet counter c1 is ahead of the c2
> + */
> +static inline int hpet_cnt_ahead(u32 c1, u32 c2)
> +{
> + return (s32)(c2 - c1) < 0;
> +}
> +
> +/*
> * Registers a IRQ handler.
> */
> int hpet_register_irq_handler(rtc_irq_handler handler)
> @@ -1075,7 +1083,7 @@ static void hpet_rtc_timer_reinit(void)
> hpet_t1_cmp += delta;
> hpet_writel(hpet_t1_cmp, HPET_T1_CMP);
> lost_ints++;
> - } while ((s32)(hpet_readl(HPET_COUNTER) - hpet_t1_cmp) > 0);
> + } while (!hpet_cnt_ahead(hpet_t1_cmp, hpet_readl(HPET_COUNTER)));

These are not equivalent for the case where the values are equal.

Let "A = hpet_t1_cmp" and "B = hpet_readl(HPET_COUNTER)"

Then "!(A > B)" means "(B - A) >= 0" not "(B - A) > 0"

Shouldn't it be:

+ } while (hpet_cnt_ahead(hpet_readl(HPET_COUNTER), hpet_t1_cmp));

Or am I missing something?

>
> if (lost_ints) {
> if (hpet_rtc_flags & RTC_PIE)
> --

--
Daniel K. Forrest Space Science and
dan.forrest@xxxxxxxxxxxxx Engineering Center
(608) 890 - 0558 University of Wisconsin, Madison
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