linux-kernel - Re: [PATCH] x86, apic: Add apic calibration hook.

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Date:	Tue, 24 Aug 2010 15:37:10 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Alok Kataria <akataria@...are.com>
cc:	"H. Peter Anvin" <hpa@...or.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, apic: Add apic calibration hook.

On Wed, 18 Aug 2010, Alok Kataria wrote:
>  
> +static void __init initialize_lapic_clkevt(long delta)
> +{
> +	/* Calculate the scaled math multiplication factor */
> +	lapic_clockevent.mult = div_sc(delta, TICK_NSEC * LAPIC_CAL_LOOPS,
> +				       lapic_clockevent.shift);
> +	lapic_clockevent.max_delta_ns =
> +		clockevent_delta2ns(0x7FFFFF, &lapic_clockevent);
> +	lapic_clockevent.min_delta_ns =
> +		clockevent_delta2ns(0xF, &lapic_clockevent);
> +}
> +
>  static int __init calibrate_APIC_clock(void)
>  {
> +	apic_calibration_res = x86_init.timers.calibrate_apic();
> +	if (apic_calibration_res) {
> +		struct clock_event_device *levt = &__get_cpu_var(lapic_events);
> +		long delta;
> +
> +		if (lapic_clockevent.mult)
> +			return 0;

  Why is this necessary ? calibrate_APIC_clock() is only called once.

Thanks,

	tglx
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