1 files changed, 39 insertions, 22 deletions

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 0b29e58f288e..57d87f79558f 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -59,7 +59,7 @@ struct cyc2ns {
 
 static DEFINE_PER_CPU_ALIGNED(struct cyc2ns, cyc2ns);
 
-void __always_inline cyc2ns_read_begin(struct cyc2ns_data *data)
+__always_inline void cyc2ns_read_begin(struct cyc2ns_data *data)
 {
 	int seq, idx;
 
@@ -76,7 +76,7 @@ void __always_inline cyc2ns_read_begin(struct cyc2ns_data *data)
 	} while (unlikely(seq != this_cpu_read(cyc2ns.seq.sequence)));
 }
 
-void __always_inline cyc2ns_read_end(void)
+__always_inline void cyc2ns_read_end(void)
 {
 	preempt_enable_notrace();
 }
@@ -632,31 +632,38 @@ unsigned long native_calibrate_tsc(void)
 
 	crystal_khz = ecx_hz / 1000;
 
-	if (crystal_khz == 0) {
-		switch (boot_cpu_data.x86_model) {
-		case INTEL_FAM6_SKYLAKE_MOBILE:
-		case INTEL_FAM6_SKYLAKE_DESKTOP:
-		case INTEL_FAM6_KABYLAKE_MOBILE:
-		case INTEL_FAM6_KABYLAKE_DESKTOP:
-			crystal_khz = 24000;	/* 24.0 MHz */
-			break;
-		case INTEL_FAM6_ATOM_GOLDMONT_X:
-			crystal_khz = 25000;	/* 25.0 MHz */
-			break;
-		case INTEL_FAM6_ATOM_GOLDMONT:
-			crystal_khz = 19200;	/* 19.2 MHz */
-			break;
-		}
-	}
+	/*
+	 * Denverton SoCs don't report crystal clock, and also don't support
+	 * CPUID.0x16 for the calculation below, so hardcode the 25MHz crystal
+	 * clock.
+	 */
+	if (crystal_khz == 0 &&
+			boot_cpu_data.x86_model == INTEL_FAM6_ATOM_GOLDMONT_X)
+		crystal_khz = 25000;
 
-	if (crystal_khz == 0)
-		return 0;
 	/*
-	 * TSC frequency determined by CPUID is a "hardware reported"
+	 * 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.
 	 */
-	setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
+	if (crystal_khz != 0)
+		setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
+
+	/*
+	 * Some Intel SoCs like Skylake and Kabylake don't report the crystal
+	 * 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 >= 0x16) {
+		unsigned int eax_base_mhz, ebx, ecx, edx;
+
+		cpuid(0x16, &eax_base_mhz, &ebx, &ecx, &edx);
+		crystal_khz = eax_base_mhz * 1000 *
+			eax_denominator / ebx_numerator;
+	}
+
+	if (crystal_khz == 0)
+		return 0;
 
 	/*
 	 * For Atom SoCs TSC is the only reliable clocksource.
@@ -665,6 +672,16 @@ unsigned long native_calibrate_tsc(void)
 	if (boot_cpu_data.x86_model == INTEL_FAM6_ATOM_GOLDMONT)
 		setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
 
+#ifdef CONFIG_X86_LOCAL_APIC
+	/*
+	 * The local APIC appears to be fed by the core crystal clock
+	 * (which sounds entirely sensible). We can set the global
+	 * lapic_timer_period here to avoid having to calibrate the APIC
+	 * timer later.
+	 */
+	lapic_timer_period = crystal_khz * 1000 / HZ;
+#endif
+
 	return crystal_khz * ebx_numerator / eax_denominator;
 }