x86: distangle user disabled TSC from unstable

tsc_enabled is set to 0 from the command line switch "notsc" and from
the mark_tsc_unstable code. Seperate those functionalities and replace
tsc_enable with tsc_disable. This makes also the native_sched_clock()
decision when to use TSC understandable.

Preparatory patch to solve the sched_clock() issue on 32 bit.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/tsc_32.c

@@ -14,7 +14,7 @@
 
 #include "mach_timer.h"
 
-static int tsc_enabled;
+static int tsc_disabled;
 
 /*
  * On some systems the TSC frequency does not
@@ -29,7 +29,7 @@ static int __init tsc_setup(char *str)
 {
 	printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, "
 	       "cannot disable TSC completely.\n");
-	mark_tsc_unstable("user disabled TSC");
+	tsc_disabled = 1;
 	return 1;
 }
 #else
@@ -120,7 +120,7 @@ unsigned long long native_sched_clock(void)
 	 *   very important for it to be as fast as the platform
 	 *   can achive it. )
 	 */
-	if (unlikely(!tsc_enabled && !tsc_unstable))
+	if (unlikely(tsc_disabled))
 		/* No locking but a rare wrong value is not a big deal: */
 		return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
 
@@ -322,7 +322,6 @@ void mark_tsc_unstable(char *reason)
 {
 	if (!tsc_unstable) {
 		tsc_unstable = 1;
-		tsc_enabled = 0;
 		printk("Marking TSC unstable due to: %s.\n", reason);
 		/* Can be called before registration */
 		if (clocksource_tsc.mult)
@@ -403,8 +402,11 @@ void __init tsc_init(void)
 {
 	int cpu;
 
-	if (!cpu_has_tsc)
+	if (!cpu_has_tsc || tsc_disabled) {
+		/* Disable the TSC in case of !cpu_has_tsc */
+		tsc_disabled = 1;
 		return;
+	}
 
 	cpu_khz = calculate_cpu_khz();
 	tsc_khz = cpu_khz;
@@ -441,8 +443,6 @@ void __init tsc_init(void)
 	if (check_tsc_unstable()) {
 		clocksource_tsc.rating = 0;
 		clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
-	} else
-		tsc_enabled = 1;
-
+	}
 	clocksource_register(&clocksource_tsc);
 }