linux-kernel - Re: [PATCH] x86,apic: Checking kernel option before detect_init

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Date:	Wed, 8 Apr 2009 16:50:41 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Rakib Mullick <rakib.mullick@...il.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86,apic: Checking kernel option before
	detect_init_APIC()


* Rakib Mullick <rakib.mullick@...il.com> wrote:

> Impact: cleanup
> 
> Before calling detect_init_APIC(), check whether apic is disabled 
> from kernel option or not.
> 
> Thanks.
> 
> Signed-off-by: Rakib Mullick <rakib.mullick@...il.com>
> 
> --- linus/arch/x86/kernel/apic.c	2009-03-26 06:26:31.000000000 +0600
> +++ rakib/arch/x86/kernel/apic.c	2009-03-26 20:47:50.116376200 +0600
> @@ -1429,10 +1429,6 @@ static int __init detect_init_APIC(void)
>  {
>  	u32 h, l, features;
> 
> -	/* Disabled by kernel option? */
> -	if (disable_apic)
> -		return -1;
> -
>  	switch (boot_cpu_data.x86_vendor) {
>  	case X86_VENDOR_AMD:
>  		if ((boot_cpu_data.x86 == 6 && boot_cpu_data.x86_model > 1) ||
> @@ -1543,8 +1539,9 @@ void __init init_apic_mappings(void)
>  	 * If no local APIC can be found then set up a fake all
>  	 * zeroes page to simulate the local APIC and another
>  	 * one for the IO-APIC.
> +	 * Check apic is disabled from kernel option or not.
>  	 */
> -	if (!smp_found_config && detect_init_APIC()) {
> +	if (!smp_found_config && (disable_apic || detect_init_APIC())) {
>  		apic_phys = (unsigned long) alloc_bootmem_pages(PAGE_SIZE);
>  		apic_phys = __pa(apic_phys);
>  	} else

Hm, are you sure this is a cleanup only? (i.e. no side-effects)

Also, even if it's a pure cleanup, wouldnt it be even cleaner to 
propagate this check into detect_init_APIC() - and thus get rid of 
the open-coded disable_apic check altogether?

	Ingo
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