[linux-yocto] [PATCH 2/2] x86 tsc: enumerate BXT tsc_khz via CPUID

2016-06-30 Thread Saul Wold 
From: Len Brown 

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 
[lenb: simplified]
Signed-off-by: Len Brown 

(cherry picked from commit dad7a9a9376716ffdf33aa719981a43cefa19ff4)
Signed-off-by: Saul Wold 
---
 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 0123365..dd85b3c 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -688,7 +688,11 @@ 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;
}
}
 
@@ -896,6 +900,8 @@ 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);
 
@@ -1256,8 +1262,16 @@ 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");
-- 
2.5.5

-- 
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[linux-yocto] [PATCH 2/2] x86 tsc: enumerate BXT tsc_khz via CPUID

2016-06-22 Thread Yong, Jonathan 
From: Bin Gao 

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 
[lenb: simplified]
Signed-off-by: Len Brown 

Signed-off-by: Yong, Jonathan 
---
 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 75df3c0..5df7ae6 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -684,7 +684,11 @@ 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;
}
}
 
@@ -882,8 +886,12 @@ 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);
@@ -1298,8 +1306,16 @@ 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");
-- 
2.7.3

-- 
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