[PATCH] i386/x86-64: Use new official CPUID to get APICID/core split on AMD platforms

Previously the apicid<->coreid split was computed based on the max
number of cores. Now use a new CPUID AMD defined for that. On most
systems right now it should be 0 and the old method will be used.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/cpu/amd.c

@@ -224,15 +224,17 @@ static void __init init_amd(struct cpuinfo_x86 *c)
 
 #ifdef CONFIG_X86_HT
 	/*
-	 * On a AMD dual core setup the lower bits of the APIC id
-	 * distingush the cores.  Assumes number of cores is a power
-	 * of two.
+	 * On a AMD multi core setup the lower bits of the APIC id
+	 * distingush the cores.
 	 */
 	if (c->x86_max_cores > 1) {
 		int cpu = smp_processor_id();
-		unsigned bits = 0;
-		while ((1 << bits) < c->x86_max_cores)
-			bits++;
+		unsigned bits = (cpuid_ecx(0x80000008) >> 12) & 0xf;
+
+		if (bits == 0) {
+			while ((1 << bits) < c->x86_max_cores)
+				bits++;
+		}
 		cpu_core_id[cpu] = phys_proc_id[cpu] & ((1<<bits)-1);
 		phys_proc_id[cpu] >>= bits;
 		printk(KERN_INFO "CPU %d(%d) -> Core %d\n",

arch/x86_64/kernel/setup.c

@@ -873,10 +873,18 @@ static void __init amd_detect_cmp(struct cpuinfo_x86 *c)
 	int node = 0;
 	unsigned apicid = hard_smp_processor_id();
 #endif
+	unsigned ecx = cpuid_ecx(0x80000008);
 
-	bits = 0;
-	while ((1 << bits) < c->x86_max_cores)
-		bits++;
+	c->x86_max_cores = (ecx & 0xff) + 1;
+
+	/* CPU telling us the core id bits shift? */
+	bits = (ecx >> 12) & 0xF;
+
+	/* Otherwise recompute */
+	if (bits == 0) {
+		while ((1 << bits) < c->x86_max_cores)
+			bits++;
+	}
 
 	/* Low order bits define the core id (index of core in socket) */
 	cpu_core_id[cpu] = phys_proc_id[cpu] & ((1 << bits)-1);
@@ -964,11 +972,9 @@ static int __init init_amd(struct cpuinfo_x86 *c)
 	if (c->x86_power & (1<<8))
 		set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability);
 
-	if (c->extended_cpuid_level >= 0x80000008) {
-		c->x86_max_cores = (cpuid_ecx(0x80000008) & 0xff) + 1;
-
+	/* Multi core CPU? */
+	if (c->extended_cpuid_level >= 0x80000008)
 		amd_detect_cmp(c);
-	}
 
 	return r;
 }