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authorDaniel Drake <drake@endlessm.com>2019-05-09 13:54:17 +0800
committerIngo Molnar <mingo@kernel.org>2019-05-09 11:06:49 +0200
commit2420a0b1798d7a78d1f9b395f09f3c80d92cc588 (patch)
tree8f74fbf9b6f1d832491369545bcce1e7637fe72e /arch/x86/kernel/tsc.c
parent52ae346bd26c7a8b17ea82e9a09671e98c5402b7 (diff)
downloadlinux-2420a0b1798d7a78d1f9b395f09f3c80d92cc588.tar.bz2
x86/tsc: Set LAPIC timer period to crystal clock frequency
The APIC timer calibration (calibrate_APIC_timer()) can be skipped in cases where we know the APIC timer frequency. On Intel SoCs, we believe that the APIC is fed by the crystal clock; this would make sense, and the crystal clock frequency has been verified against the APIC timer calibration result on ApolloLake, GeminiLake, Kabylake, CoffeeLake, WhiskeyLake and AmberLake. Set lapic_timer_period based on the crystal clock frequency accordingly. APIC timer calibration would normally be skipped on modern CPUs by nature of the TSC deadline timer being used instead, however this change is still potentially useful, e.g. if the TSC deadline timer has been disabled with a kernel parameter. calibrate_APIC_timer() uses the legacy timer, but we are seeing new platforms that omit such legacy functionality, so avoiding such codepaths is becoming more important. Suggested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Daniel Drake <drake@endlessm.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: len.brown@intel.com Cc: linux@endlessm.com Cc: rafael.j.wysocki@intel.com Link: http://lkml.kernel.org/r/20190509055417.13152-3-drake@endlessm.com Link: https://lkml.kernel.org/r/20190419083533.32388-1-drake@endlessm.com Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1904031206440.1967@nanos.tec.linutronix.de Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/tsc.c')
-rw-r--r--arch/x86/kernel/tsc.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 6e6d933fb99c..8f47c4862c56 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -671,6 +671,16 @@ 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;
}