From: Bin Gao <bin....@intel.com>
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.
Signed-off-by: Bin Gao <bin....@intel.com>
[lenb: simplified]
Signed-off-by: Len Brown <len.br...@intel.com>
---
arch/x86/kernel/tsc.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index ca41c30..64dc998 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;
}
}
@@ -891,8 +895,12 @@ int recalibrate_cpu_khz(void)
if (cpu_has_tsc) {
cpu_khz = x86_platform.calibrate_cpu();
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);
@@ -1305,8 +1313,16 @@ 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");
--
2.8.0.rc4.16.g56331f8
