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x86/tsc: Enumerate BXT tsc_khz via CPUID 

Hard code the BXT crystal clock (aka ART - Always Running Timer)
to 19.200 MHz, and use CPUID leaf 0x15 to determine the BXT TSC frequency.

Use tsc_khz to sanity check BXT cpu_khz,
which can be erroneous in some configurations.

(I simplified the original patch from Bin Gao.)

Original-From: Bin Gao <bin.gao@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/bf4e7c175acd6d09719c47c319b10ff1f0627ff8.1466138954.git.len.brown@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Len Brown 2016-06-17 01:22:52 -04:00 committed by Ingo Molnar
parent aa297292d7
commit ff4c86635e
1 changed files with 15 additions and 1 deletions
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16
arch/x86/kernel/tsc.c
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@ -693,7 +693,11 @@ unsigned long native_calibrate_tsc(void)
switch (boot_cpu_data.x86_model) {
case 0x4E: /* SKL */
case 0x5E: /* SKL */
crystal_khz = 24000; /* 24 MHz */
crystal_khz = 24000; /* 24.0 MHz */
break;
case 0x5C: /* BXT */
crystal_khz = 19200; /* 19.2 MHz */
break;
}
}
@ -895,6 +899,8 @@ int recalibrate_cpu_khz(void)
tsc_khz = x86_platform.calibrate_tsc();
if (tsc_khz == 0)
tsc_khz = cpu_khz;
else if (abs(cpu_khz - tsc_khz) * 10 > tsc_khz)
cpu_khz = tsc_khz;
cpu_data(0).loops_per_jiffy = cpufreq_scale(cpu_data(0).loops_per_jiffy,
cpu_khz_old, cpu_khz);
@ -1302,8 +1308,16 @@ void __init tsc_init(void)
cpu_khz = x86_platform.calibrate_cpu();
tsc_khz = x86_platform.calibrate_tsc();
/*
* Trust non-zero tsc_khz as authorative,
* and use it to sanity check cpu_khz,
* which will be off if system timer is off.
*/
if (tsc_khz == 0)
tsc_khz = cpu_khz;
else if (abs(cpu_khz - tsc_khz) * 10 > tsc_khz)
cpu_khz = tsc_khz;
if (!tsc_khz) {
mark_tsc_unstable("could not calculate TSC khz");