x86/tsc: Add the Intel Denverton Processor to native_calibrate_tsc()

The Intel Denverton microserver uses a 25 MHz TSC crystal,
so we can derive its exact [*] TSC frequency
using CPUID and some arithmetic, eg.:

  TSC: 1800 MHz (25000000 Hz * 216 / 3 / 1000000)

[*] 'exact' is only as good as the crystal, which should be +/- 20ppm

Signed-off-by: Len Brown <len.brown@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/306899f94804aece6d8fa8b4223ede3b48dbb59c.1484287748.git.len.brown@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index be3a49ee035650f1f1eac68c07ad0e8898c40585..e41af597aed8e2e454965f8459f26b372c091b4f 100644 (file)
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -694,6 +694,7 @@ unsigned long native_calibrate_tsc(void)
                        crystal_khz = 24000;    /* 24.0 MHz */
                        break;
                case INTEL_FAM6_SKYLAKE_X:
+               case INTEL_FAM6_ATOM_DENVERTON:
                        crystal_khz = 25000;    /* 25.0 MHz */
                        break;
                case INTEL_FAM6_ATOM_GOLDMONT: