Commit-ID: a3dc6a4c9c329bf6ac4ee996c67557664d6b780e Gitweb: http://git.kernel.org/tip/a3dc6a4c9c329bf6ac4ee996c67557664d6b780e Author: Len Brown <len.br...@intel.com> AuthorDate: Fri, 17 Jun 2016 01:22:52 -0400 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Sun, 10 Jul 2016 17:00:14 +0200
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....@intel.com> Signed-off-by: Len Brown <len.br...@intel.com> Reviewed-by: Thomas Gleixner <t...@linutronix.de> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Link: http://lkml.kernel.org/r/bf4e7c175acd6d09719c47c319b10ff1f0627ff8.1466138954.git.len.br...@intel.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- arch/x86/kernel/tsc.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index e1496b7..2a952fc 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -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");
