Change in coreboot[master]: arch/x86: SMBIOS: Improve core count reporting

[Patrick Georgi (Code Review)]

Patrick Georgi has submitted this change. ( https://review.coreboot.org/c/coreboot/+/36941 )

Change subject: arch/x86: SMBIOS: Improve core count reporting
......................................................................

arch/x86: SMBIOS: Improve core count reporting

Current code uses CPUID leaf 0x1, EBX bits 16:23 to determine number for
"core count". However, it turns out this number has little to do with
real number of cores. According to SDM vol 2A, it stays for "maximum
number of addressable IDs for logical processors in this physical
package". This does not seem to take into account fusing of giving
processor.

The new code determines 'core count' by dividing thread-level cpus by
reported logical cores. This seems to be the only way to arrive
to number of cores as it is reported in official CPU datasheet.

TEST=tested on OCP monolake

Change-Id: Id4ba9e3079f92ffe38f9104ffcfafe62582dd259
Signed-off-by: Andrey Petrov 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36941
Tested-by: build bot (Jenkins) 
Reviewed-by: Werner Zeh 
---
M src/arch/x86/smbios.c
1 file changed, 20 insertions(+), 1 deletion(-)

Approvals:
  build bot (Jenkins): Verified
  Werner Zeh: Looks good to me, approved

diff --git a/src/arch/x86/smbios.c b/src/arch/x86/smbios.c
index 7e05408..a599add 100644
--- a/src/arch/x86/smbios.c
+++ b/src/arch/x86/smbios.c
@@ -647,7 +647,26 @@
    t->processor_version = smbios_processor_name(t->eos);
    t->processor_family = (res.eax > 0) ? 0x0c : 0x6;
    t->processor_type = 3; /* System Processor */
-	t->core_count = (res.ebx >> 16) & 0xff;
+	/*
+	 * If CPUID leaf 11 is available, calculate "core count" by dividing
+	 * SMT_ID (logical processors in a core) by Core_ID (number of cores).
+	 * This seems to be the way to arrive to a number of cores mentioned on
+	 * ark.intel.com.
+	 */
+	if (cpu_have_cpuid() && cpuid_get_max_func() >= 0xb) {
+		uint32_t leaf_b_cores = 0, leaf_b_threads = 0;
+		res = cpuid_ext(0xb, 1);
+		leaf_b_cores = res.ebx;
+		res = cpuid_ext(0xb, 0);
+		leaf_b_threads = res.ebx;
+		/* if hyperthreading is not available, pretend this is 1 */
+		if (leaf_b_threads == 0) {
+			leaf_b_threads = 1;
+		}
+		t->core_count = leaf_b_cores / leaf_b_threads;
+	} else {
+		t->core_count = (res.ebx >> 16) & 0xff;
+	}
    /* Assume we enable all the cores always, capped only by MAX_CPUS */
    t->core_enabled = MIN(t->core_count, CONFIG_MAX_CPUS);
    t->l1_cache_handle = 0xffff;