[PATCH v6 23/51] x86/tsc: Add standalone helper for getting CPU frequency from CPUID

Extract the guts of cpu_khz_from_cpuid() to a standalone helper that
doesn't restrict the usage to Intel CPUs.  This will allow sharing the
core logic with KVM-as-a-guest, as KVM generally doesn't restrict CPUID
based on vendor.

No functional change intended.

Reviewed-by: David Woodhouse <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
 arch/x86/include/asm/tsc.h |  1 +
 arch/x86/kernel/tsc.c      | 31 +++++++++++++++----------------
 2 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index c09ec485abcd..cb682f097ea7 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -88,6 +88,7 @@ struct cpuid_tsc_info {
 	unsigned int crystal_khz;
 };
 extern int cpuid_get_tsc_info(struct cpuid_tsc_info *info);
+extern unsigned int __cpu_khz_from_cpuid(void);
 
 extern void tsc_early_init(void);
 extern void tsc_init(void);
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index d95e4f059f17..4c5328d19ebe 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -668,6 +668,18 @@ int cpuid_get_tsc_info(struct cpuid_tsc_info *info)
 	return 0;
 }
 
+unsigned int __cpu_khz_from_cpuid(void)
+{
+	unsigned int eax_base_mhz, ebx, ecx, edx;
+
+	if (boot_cpu_data.cpuid_level < CPUID_LEAF_FREQ)
+		return 0;
+
+	cpuid(CPUID_LEAF_FREQ, &eax_base_mhz, &ebx, &ecx, &edx);
+
+	return eax_base_mhz * 1000;
+}
+
 /**
  * native_calibrate_tsc - determine TSC frequency
  * Determine TSC frequency via CPUID, else return 0.
@@ -703,12 +715,8 @@ static unsigned long native_calibrate_tsc(void)
 	 * clock, but we can easily calculate it to a high degree of accuracy
 	 * by considering the crystal ratio and the CPU speed.
 	 */
-	if (!info.crystal_khz && boot_cpu_data.cpuid_level >= CPUID_LEAF_FREQ) {
-		unsigned int eax_base_mhz, ebx, ecx, edx;
-
-		cpuid(CPUID_LEAF_FREQ, &eax_base_mhz, &ebx, &ecx, &edx);
-		info.crystal_khz = eax_base_mhz * 1000 * info.denominator / info.numerator;
-	}
+	if (!info.crystal_khz)
+		info.crystal_khz = __cpu_khz_from_cpuid() * info.denominator / info.numerator;
 
 	if (!info.crystal_khz)
 		return 0;
@@ -733,19 +741,10 @@ static unsigned long native_calibrate_tsc(void)
 
 static unsigned long cpu_khz_from_cpuid(void)
 {
-	unsigned int eax_base_mhz, ebx_max_mhz, ecx_bus_mhz, edx;
-
 	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
 		return 0;
 
-	if (boot_cpu_data.cpuid_level < CPUID_LEAF_FREQ)
-		return 0;
-
-	eax_base_mhz = ebx_max_mhz = ecx_bus_mhz = edx = 0;
-
-	cpuid(CPUID_LEAF_FREQ, &eax_base_mhz, &ebx_max_mhz, &ecx_bus_mhz, &edx);
-
-	return eax_base_mhz * 1000;
+	return __cpu_khz_from_cpuid();
 }
 
 /*
-- 
2.55.0.679.g6767b8d81c-goog