Re: [PATCH] x86: better CPU identification without the CPUID

["Yinghai Lu" <yhlu.kernel@gmail.com>]

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On Sat, Sep 13, 2008 at 9:43 PM, Yinghai Lu <yhlu.kernel@gmail.com> wrote:
> On Sat, Sep 13, 2008 at 3:56 AM, Krzysztof Helt <krzysztof.h1@wp.pl> wrote:
>> From: Krzysztof Helt <krzysztof.h1@wp.pl>
>>
>> cpus without the CPUID instruction are identified
>> as general 386 or 486 while some cpus (mostly made
>> by Cyrix) provide c_identify function which identify
>> correctly older cpus using cpu specific registers).
>>
>> Cyrix cpus are even worse as 5x86 and 6x68 have
>> the CPUID instruction disabled. The CPUID is
>> enabled by the c_identify() but the c_identify
>> is only called when the CPUID is available.
>>
>> Fix this by calling the c_identify() for all known
>> cpu families if there is no the CPUID instruction

I updated it to tip/master and call that in early_identify_cpu. it
should solve mtrr detection for Cyrix ...

Please check attached patch.

Thanks

YH

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[PATCH] x86: identify_cpu_without_cpuid

need to call c_identify() for cpus without cpuid earlier...

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>

---
 arch/x86/kernel/cpu/common.c |   63 +++++++++++++++++++++++++++----------------
 1 file changed, 40 insertions(+), 23 deletions(-)

Index: linux-2.6/arch/x86/kernel/cpu/common.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/cpu/common.c
+++ linux-2.6/arch/x86/kernel/cpu/common.c
@@ -485,6 +485,33 @@ static void __cpuinit get_cpu_cap(struct
 		c->x86_power = cpuid_edx(0x80000007);
 
 }
+
+static void __cpuinit identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
+{
+#ifdef CONFIG_X86_32
+	int i;
+
+	/*
+	 * First of all, decide if this is a 486 or higher
+	 * It's a 486 if we can modify the AC flag
+	 */
+	if (flag_is_changeable_p(X86_EFLAGS_AC))
+		c->x86 = 4;
+	else
+		c->x86 = 3;
+
+	for (i = 0; i < X86_VENDOR_NUM; i++)
+		if (cpu_devs[i] && cpu_devs[i]->c_identify) {
+			c->x86_vendor_id[0] = 0;
+			cpu_devs[i]->c_identify(c);
+			if (c->x86_vendor_id[0]) {
+				get_cpu_vendor(c);
+				break;
+			}
+		}
+#endif
+}
+
 /*
  * Do minimum CPU detection early.
  * Fields really needed: vendor, cpuid_level, family, model, mask,
@@ -503,18 +530,17 @@ static void __init early_identify_cpu(st
 #endif
 	c->x86_cache_alignment = c->x86_clflush_size;
 
-	if (!have_cpuid_p())
-		return;
-
 	memset(&c->x86_capability, 0, sizeof c->x86_capability);
-
 	c->extended_cpuid_level = 0;
 
-	cpu_detect(c);
-
-	get_cpu_vendor(c);
-
-	get_cpu_cap(c);
+	if (!have_cpuid_p()) {
+		identify_cpu_without_cpuid(c);
+		return;
+	} else {
+		cpu_detect(c);
+		get_cpu_vendor(c);
+		get_cpu_cap(c);
+	}
 
 	if (this_cpu->c_early_init)
 		this_cpu->c_early_init(c);
@@ -583,11 +609,13 @@ static void __cpuinit detect_nopl(struct
 
 static void __cpuinit generic_identify(struct cpuinfo_x86 *c)
 {
-	if (!have_cpuid_p())
-		return;
-
 	c->extended_cpuid_level = 0;
 
+	if (!have_cpuid_p()) {
+		identify_cpu_without_cpuid(c);
+		return;
+	}
+
 	cpu_detect(c);
 
 	get_cpu_vendor(c);
@@ -639,17 +667,6 @@ static void __cpuinit identify_cpu(struc
 	c->x86_cache_alignment = c->x86_clflush_size;
 	memset(&c->x86_capability, 0, sizeof c->x86_capability);
 
-	if (!have_cpuid_p()) {
-		/*
-		 * First of all, decide if this is a 486 or higher
-		 * It's a 486 if we can modify the AC flag
-		 */
-		if (flag_is_changeable_p(X86_EFLAGS_AC))
-			c->x86 = 4;
-		else
-			c->x86 = 3;
-	}
-
 	generic_identify(c);
 
 	if (this_cpu->c_identify)