linux-kernel - i686 quirk for AMD Geode

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Date:	Sat, 3 Oct 2009 04:12:47 +0200
From:	Matteo Croce <technoboy85@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org
Subject: i686 quirk for AMD Geode

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();
--
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