x86: Add cpu capability flag X86_FEATURE_NONSTOP_TSC_S3

On some new Intel Atom processors (Penwell and Cloverview), there is
a feature that the TSC won't stop in S3 state, say the TSC value
won't be reset to 0 after resume. This feature makes TSC a more reliable
clocksource and could benefit the timekeeping code during system
suspend/resume cycle, so add a flag for it.

Signed-off-by: Feng Tang <feng.tang@intel.com>
[jstultz: Fix checkpatch warning]
Signed-off-by: John Stultz <john.stultz@linaro.org>

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 93fe929..a8466f2 100644 (file)
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -100,6 +100,7 @@
 #define X86_FEATURE_AMD_DCM     (3*32+27) /* multi-node processor */
 #define X86_FEATURE_APERFMPERF (3*32+28) /* APERFMPERF */
 #define X86_FEATURE_EAGER_FPU  (3*32+29) /* "eagerfpu" Non lazy FPU restore */
+#define X86_FEATURE_NONSTOP_TSC_S3 (3*32+30) /* TSC doesn't stop in S3 state */
 
 /* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
 #define X86_FEATURE_XMM3       (4*32+ 0) /* "pni" SSE-3 */

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 1905ce9..e7ae0d8 100644 (file)
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -96,6 +96,18 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
                        sched_clock_stable = 1;
        }
 
+       /* Penwell and Cloverview have the TSC which doesn't sleep on S3 */
+       if (c->x86 == 6) {
+               switch (c->x86_model) {
+               case 0x27:      /* Penwell */
+               case 0x35:      /* Cloverview */
+                       set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC_S3);
+                       break;
+               default:
+                       break;
+               }
+       }
+
        /*
         * There is a known erratum on Pentium III and Core Solo
         * and Core Duo CPUs.