@@ -105,6 +105,7 @@
#define X86_FEATURE_AMD_DCM ( 3*32+27) /* multi-node processor */
#define X86_FEATURE_APERFMPERF ( 3*32+28) /* APERFMPERF */
#define X86_FEATURE_NONSTOP_TSC_S3 ( 3*32+30) /* TSC doesn't stop in S3 state */
+#define X86_FEATURE_TSC_KNOWN_FREQ ( 3*32+31) /* TSC has known frequency */
/* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
#define X86_FEATURE_XMM3 ( 4*32+ 0) /* "pni" SSE-3 */
@@ -1222,10 +1222,15 @@ static int __init init_tsc_clocksource(void)
clocksource_tsc.flags |= CLOCK_SOURCE_SUSPEND_NONSTOP;
/*
- * Trust the results of the earlier calibration on systems
- * exporting a reliable TSC.
+ * When TSC frequency is known (retrieved via MSR or CPUID), we skip
+ * the refined calibration and directly register it as a clocksource.
+ *
+ * We still keep the TSC_RELIABLE flag here to avoid regressions -
+ * it will be removed after all the conversion for other code paths
+ * connected to this flag is done.
*/
- if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) {
+ if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE) ||
+ boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ)) {
clocksource_register_khz(&clocksource_tsc, tsc_khz);
return 0;
}