x86, tsc: Skip TSC synchronization checks for tsc=reliable

tsc=reliable boot parameter is supposed to skip all the TSC
stablility checks during boot time.

On a 8-socket system where we want to run an experiment with the
"tsc=reliable" boot option, TSC synchronization checks are not
getting skipped and marking the TSC as not stable.

Check for tsc_clocksource_reliable (which is set via
tsc=reliable or for platforms supporting synthetic TSC_RELIABLE
feature bit etc) and when set, skip the TSC synchronization
tests during boot.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Acked-by: John Stultz <johnstul@us.ibm.com>
Tested-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1320446537.15071.14.camel@sbsiddha-desk.sc.intel.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/tsc.h

@@ -51,6 +51,8 @@ extern int unsynchronized_tsc(void);
 extern int check_tsc_unstable(void);
 extern unsigned long native_calibrate_tsc(void);
 
+extern int tsc_clocksource_reliable;
+
 /*
  * Boot-time check whether the TSCs are synchronized across
  * all CPUs/cores:

arch/x86/kernel/tsc.c

@@ -35,7 +35,7 @@ static int __read_mostly tsc_unstable;
    erroneous rdtsc usage on !cpu_has_tsc processors */
 static int __read_mostly tsc_disabled = -1;
 
-static int tsc_clocksource_reliable;
+int tsc_clocksource_reliable;
 /*
  * Scheduler clock - returns current time in nanosec units.
  */

arch/x86/kernel/tsc_sync.c

@@ -113,7 +113,7 @@ void __cpuinit check_tsc_sync_source(int cpu)
 	if (unsynchronized_tsc())
 		return;
 
-	if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) {
+	if (tsc_clocksource_reliable) {
 		if (cpu == (nr_cpu_ids-1) || system_state != SYSTEM_BOOTING)
 			pr_info(
 			"Skipped synchronization checks as TSC is reliable.\n");
@@ -172,7 +172,7 @@ void __cpuinit check_tsc_sync_target(void)
 {
 	int cpus = 2;
 
-	if (unsynchronized_tsc() || boot_cpu_has(X86_FEATURE_TSC_RELIABLE))
+	if (unsynchronized_tsc() || tsc_clocksource_reliable)
 		return;
 
 	/*