[PATCH v5 09/51] x86/tsc: Add a standalone helper for getting TSC info from CPUID.0x15

[Sean Christopherson <seanjc@google.com>]

Extract retrieval of TSC frequency information from CPUID into a standalone
helper so that TDX guest support can reuse the logic.

Opportunistically drop native_calibrate_tsc()'s "== 0" and "!= 0" checks
in favor of the kernel's preferred style.

No functional change intended.

Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kernel/tsc.c | 61 +++++++++++++++++++++++++++----------------
 1 file changed, 38 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index f049c126e47c..12043812c8f5 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -645,46 +645,62 @@ static unsigned long quick_pit_calibrate(void)
 	return delta;
 }
 
+struct cpuid_tsc_info {
+	unsigned int denominator;
+	unsigned int numerator;
+	unsigned int crystal_khz;
+};
+
+static int cpuid_get_tsc_info(struct cpuid_tsc_info *info)
+{
+	unsigned int ecx_hz, edx;
+
+	if (boot_cpu_data.cpuid_level < CPUID_LEAF_TSC)
+		return -ENOENT;
+
+	/* CPUID 15H TSC/Crystal ratio, plus optionally Crystal Hz */
+	cpuid(CPUID_LEAF_TSC, &info->denominator, &info->numerator, &ecx_hz, &edx);
+
+	if (!info->denominator || !info->numerator)
+		return -ENOENT;
+
+	/*
+	 * Note: some CPUs provide the multiplier information, but not the core
+	 * crystal frequency.  The multiplier information is still useful for
+	 * such CPUs, as the crystal frequency can be gleaned from CPUID.0x16.
+	 */
+	info->crystal_khz = ecx_hz / 1000;
+	return 0;
+}
+
 /**
  * native_calibrate_tsc - determine TSC frequency
  * Determine TSC frequency via CPUID, else return 0.
  */
 unsigned long native_calibrate_tsc(void)
 {
-	unsigned int eax_denominator, ebx_numerator, ecx_hz, edx;
-	unsigned int crystal_khz;
+	struct cpuid_tsc_info info;
 
 	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
 		return 0;
 
-	if (boot_cpu_data.cpuid_level < CPUID_LEAF_TSC)
+	if (cpuid_get_tsc_info(&info))
 		return 0;
 
-	eax_denominator = ebx_numerator = ecx_hz = edx = 0;
-
-	/* CPUID 15H TSC/Crystal ratio, plus optionally Crystal Hz */
-	cpuid(CPUID_LEAF_TSC, &eax_denominator, &ebx_numerator, &ecx_hz, &edx);
-
-	if (ebx_numerator == 0 || eax_denominator == 0)
-		return 0;
-
-	crystal_khz = ecx_hz / 1000;
-
 	/*
 	 * Denverton SoCs don't report crystal clock, and also don't support
 	 * CPUID_LEAF_FREQ for the calculation below, so hardcode the 25MHz
 	 * crystal clock.
 	 */
-	if (crystal_khz == 0 &&
-			boot_cpu_data.x86_vfm == INTEL_ATOM_GOLDMONT_D)
-		crystal_khz = 25000;
+	if (!info.crystal_khz && boot_cpu_data.x86_vfm == INTEL_ATOM_GOLDMONT_D)
+		info.crystal_khz = 25000;
 
 	/*
 	 * TSC frequency reported directly by CPUID is a "hardware reported"
 	 * frequency and is the most accurate one so far we have. This
 	 * is considered a known frequency.
 	 */
-	if (crystal_khz != 0)
+	if (info.crystal_khz)
 		setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
 
 	/*
@@ -692,15 +708,14 @@ 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 (crystal_khz == 0 && boot_cpu_data.cpuid_level >= CPUID_LEAF_FREQ) {
+	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);
-		crystal_khz = eax_base_mhz * 1000 *
-			eax_denominator / ebx_numerator;
+		info.crystal_khz = eax_base_mhz * 1000 * info.denominator / info.numerator;
 	}
 
-	if (crystal_khz == 0)
+	if (!info.crystal_khz)
 		return 0;
 
 	/*
@@ -716,9 +731,9 @@ unsigned long native_calibrate_tsc(void)
 	 * lapic_timer_period here to avoid having to calibrate the APIC
 	 * timer later.
 	 */
-	apic_set_timer_period_khz(crystal_khz, "CPUID 0x15/0x16");
+	apic_set_timer_period_khz(info.crystal_khz, "CPUID 0x15/0x16");
 
-	return crystal_khz * ebx_numerator / eax_denominator;
+	return info.crystal_khz * info.numerator / info.denominator;
 }
 
 static unsigned long cpu_khz_from_cpuid(void)
-- 
2.55.0.rc0.799.gd6f94ed593-goog