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Subject[PATCH 1/3] x86/tsc: Future-proof native_calibrate_tsc()
From: Len Brown <>

If native_calibrate_tsc() can not discover the TSC frequency,
via CPUID or via built-in table, it must return without
will prevent TSC refined calibration.

This patch allows Linux to correctly support future Intel hardware,
that has (cpu_khz != tsc_khz), and support for CPUID.15
without support for CPUID.15.crystal_khz.

This patch is needed since X86_FEATURE_TSC_KNOWN_FREQ was added in Linux-4.10:

commit 4ca4df0b7eb0
("x86/tsc: Mark TSC frequency determined by CPUID as known")

If not applied, such systems will run with tsc_khz = cpu_khz,
which may result in under-stated TSC rate, and time-of-day drift.

Signed-off-by: Len Brown <>
Cc: Bin Gao <>
Cc: <> # v4.10+
arch/x86/kernel/tsc.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 8ea117f8142e..ce4b71119c36 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -612,6 +612,8 @@ unsigned long native_calibrate_tsc(void)

+ if (crystal_khz == 0)
+ return 0;
* TSC frequency determined by CPUID is a "hardware reported"
* frequency and is the most accurate one so far we have. This
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