linux-kernel - Re: i686 quirk for AMD Geode

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Date:	Sat, 3 Oct 2009 09:21:27 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Matteo Croce <technoboy85@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: i686 quirk for AMD Geode


* Matteo Croce <technoboy85@...il.com> wrote:

> Hi,
> 
> the AMD GEode LX has an x86 id of 5 (i586) tought it's technically an i686:
> 
> root@...x:/usr/src# cat /proc/cpuinfo
> processor       : 0
> vendor_id       : AuthenticAMD
> cpu family      : 5
> model           : 10
> model name      : Geode(TM) Integrated Processor by AMD PCS
> stepping        : 2
> cpu MHz         : 498.060
> cache size      : 128 KB
> fdiv_bug        : no
> hlt_bug         : no
> f00f_bug        : no
> coma_bug        : no
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 1
> wp              : yes
> flags           : fpu de pse tsc msr cx8 sep pge cmov clflush mmx
> mmxext 3dnowext 3dnow
> bogomips        : 996.12
> clflush size    : 32
> cache_alignment : 32
> address sizes   : 32 bits physical, 32 bits virtual
> power management:
> 
> indeed it has mmx, mmxext and cmov.
> So I added the quirk below and I can confirm that the system is running fine.
> I did an x264 encode to trigger any SIGILL due to missing opcodes, but
> it worked.
> 
> I also did this simple test which gives a ~2.5x speed boost:
> http://pastebin.ca/1590089
> 
> I wish some feedback from someone, I really dunno why AMD set the
> cpuid value to 5
> 
> --- a/arch/x86/kernel/cpu/bugs.c	2009-10-03 03:43:02.399323313 +0200
> +++ b/arch/x86/kernel/cpu/bugs.c	2009-10-03 03:54:22.582205090 +0200
> @@ -151,6 +151,12 @@
>  #endif
>  }
> 
> +static void __init check_geode_i586(void)
> +{
> +	if(boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
> +	   boot_cpu_data.x86_model == 10 && boot_cpu_data.x86 == 5)
> +		boot_cpu_data.x86 = 6;
> +}
> 
>  void __init check_bugs(void)
>  {
> @@ -163,6 +169,7 @@
>  	check_fpu();
>  	check_hlt();
>  	check_popad();
> +	check_geode_i586();
>  	init_utsname()->machine[1] =
>  		'0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
>  	alternative_instructions();

Looks good, but your signoff line is missing.

	Ingo
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