linux-kernel - Re: [PATCH 2/2] x86/apic: check global clockevent in lapic timer setup

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Date:	Thu, 17 Dec 2009 22:41:48 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"Pan, Jacob jun" <jacob.jun.pan@...el.com>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 2/2] x86/apic: check global clockevent in lapic timer
	setup

On Thu, Dec 17, 2009 at 09:59:23AM -0800, Pan, Jacob jun wrote:
> From: Jacob Pan <jacob.jun.pan@...el.com>
> Date: Thu, 17 Dec 2009 08:07:57 -0800
> Subject: [PATCH 2/2] x86/apic: check global clockevent in lapic timer setup
> 
> Global clockevent is needed to calibrate local apic timer.
> This patch makes sure we have a valid global clockevent prior
> to lapic timer setup.
> Non-pc x86 mid platform with per cpu platform timer may not
> have a global clockevent device.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@...el.com>
> ---
>  arch/x86/kernel/apic/apic.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index aa57c07..7e7aee1 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -724,6 +724,13 @@ static int __init calibrate_APIC_clock(void)
>   */
>  void __init setup_boot_APIC_clock(void)
>  {
> +	/* global clockevent is needed for calibration */
> +	if (!global_clock_event) {
> +		apic_printk(APIC_DEBUG,
> +				"no global clockevent for calibration\n");
> +		return;
> +	}
> +
>  	/*
>  	 * The local apic timer can be disabled via the kernel
>  	 * commandline or from the CPU detection code. Register the lapic
> -- 
> 1.6.5.3
>

Hi Jacob,

Wouldn't be better to operate the same way as in case of "noapictimer"
boot option. I guess the non-pc x86 midplatforms you're mentioning
do not use SMP ever but just to be consistent in code.

Perhaps something like:

void __init setup_boot_APIC_clock(void) {

	if (!global_clock_event) {
		pr_info("No global clockevent for calibration\n");
		disable_apic_timer = 1;
	}

	if (disable_apic_timer) {
		pr_info("Disabling APIC timer\n");
		/* No broadcast on UP ! */
		if (num_possible_cpus() > 1) {
			lapic_clockevent.mult = 1;
			setup_APIC_timer();
		}
		return;
	}

	...
}

Or I miss something?

	-- Cyrill
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