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Commit ff4c8663 authored by Len Brown's avatar Len Brown Committed by Ingo Molnar
Browse files

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: default avatarLen Brown <len.brown@intel.com>
Reviewed-by: default avatarThomas 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: default avatarIngo Molnar <mingo@kernel.org>
parent aa297292

arch/x86/kernel/tsc.c

+15 −1
Original line number Diff line number Diff line
@@ -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");