linux-kernel - Re: [X86] Add a boot parameter to force-enable PAT

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Date:	Wed, 21 May 2008 03:10:21 +0200
From:	Rene Herman <rene.herman@...access.nl>
To:	Dave Jones <davej@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Rene Herman <rene.herman@...access.nl>,
	Mikael Pettersson <mikpe@...uu.se>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [X86] Add a boot parameter to force-enable PAT

On 21-05-08 00:56, Dave Jones wrote:

> Not boot-tested, but it compiles for me..

It doesn't even apply for me. Moreover though -- __early_param() still 
seems to be too late for validate_pat_support() so this isn't going to work.

__setup() is even later than that. I guess this just wants to set a flag 
from validate_pat_support() which arch/x86/mm/pat.c can then check later?

> --- a/arch/x86/kernel/cpu/addon_cpuid_features.c
> +++ b/arch/x86/kernel/cpu/addon_cpuid_features.c
> @@ -51,8 +51,15 @@ void __cpuinit init_scattered_cpuid_features(struct cpuinfo_x86 *c)
>  }
>  
>  #ifdef CONFIG_X86_PAT
> +int forcepat;
> +
>  void __cpuinit validate_pat_support(struct cpuinfo_x86 *c)
>  {
> +	if (forcepat == 1) {
> +		printk(KERN_INFO "Force enabling PAT\n");
> +		return;
> +	}
> +
>  	switch (c->x86_vendor) {
>  	case X86_VENDOR_AMD:
>  		if (c->x86 >= 0xf && c->x86 <= 0x11)
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index e83b770..7429bee 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -25,8 +25,11 @@
>  #include <asm/mtrr.h>
>  #include <asm/io.h>
>  
> +static int debug_enable;
> +
>  #ifdef CONFIG_X86_PAT
>  int __read_mostly pat_wc_enabled = 1;
> +extern int forcepat;
>  
>  void __cpuinit pat_disable(char *reason)
>  {
> @@ -34,23 +37,22 @@ void __cpuinit pat_disable(char *reason)
>  	printk(KERN_INFO "%s\n", reason);
>  }
>  
> -static int nopat(char *str)
> +static int __init patsetup(char *str)
>  {
> -	pat_disable("PAT support disabled.");
> +	if (strcmp("force", str) == 0) {
> +		forcepat = 1;
> +		printk(KERN_INFO "Force enabling PAT\n");
> +	}
> +	if (strcmp("off", str) == 0)
> +		pat_disable("PAT support disabled.");
> +	if (strcmp("debug", str) == 0)
> +		debug_enable = 1;
>  	return 0;
>  }
> -early_param("nopat", nopat);
> +early_param("pat=", patsetup);
>  #endif
>  
>  
> -static int debug_enable;
> -static int __init pat_debug_setup(char *str)
> -{
> -	debug_enable = 1;
> -	return 0;
> -}
> -__setup("debugpat", pat_debug_setup);
> -
>  #define dprintk(fmt, arg...) \
>  	do { if (debug_enable) printk(KERN_INFO fmt, ##arg); } while (0)
>  
> 

Rene.

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