diff -r ea6a9793928d xen/arch/x86/time.c
--- a/xen/arch/x86/time.c	Tue Jul 15 18:00:13 2008 +0100
+++ b/xen/arch/x86/time.c	Thu Jul 17 14:34:24 2008 -0600
@@ -484,7 +484,7 @@ static int init_pmtimer(struct platform_
  * PLATFORM TIMER 5: TSC
  */
 
-#define platform_timer_is_tsc() (!strcmp(plt_src.name, "TSC"))
+#define platform_timer_is_tsc() (plt_src.counter_bits == 64)
 static u64 tsc_freq;
 
 static u64 read_tsc_count(void)
@@ -496,22 +496,7 @@ static u64 read_tsc_count(void)
 
 static int init_tsctimer(struct platform_timesource *pts)
 {
-    unsigned int cpu;
-
-    /*
-     * TODO: evaluate stability of TSC here, return 0 if not stable.
-     * For now we assume all TSCs are synchronised and hence can all share
-     * CPU 0's calibration values.
-     */
-    for_each_cpu ( cpu )
-    {
-        if ( cpu == 0 )
-            continue;
-        memcpy(&per_cpu(cpu_time, cpu),
-               &per_cpu(cpu_time, 0),
-               sizeof(struct cpu_time));
-    }
-
+    /* TODO: evaluate stability of TSC here, return 0 if not stable */
     pts->name = "TSC";
     pts->frequency = tsc_freq;
     pts->read_counter = read_tsc_count;
@@ -541,6 +526,7 @@ static void plt_overflow(void *unused)
 {
     u64 count;
 
+    ASSERT(plt_src.counter_bits <= 32);
     spin_lock(&platform_timer_lock);
     count = plt_src.read_counter();
     plt_stamp64 += (count - plt_stamp) & plt_mask;
@@ -575,6 +561,8 @@ static void platform_time_calibration(vo
     u64 count;
     s_time_t stamp;
 
+    if ( plt_src.counter_bits == 64 )
+        return;
     spin_lock(&platform_timer_lock);
     count = plt_stamp64 + ((plt_src.read_counter() - plt_stamp) & plt_mask);
     stamp = __read_platform_stime(count);
@@ -585,6 +573,8 @@ static void platform_time_calibration(vo
 
 static void resume_platform_timer(void)
 {
+    if ( plt_src.counter_bits == 64 )
+        return;
     /* No change in platform_stime across suspend/resume. */
     platform_timer_stamp = plt_stamp64;
     plt_stamp = plt_src.read_counter();
@@ -624,12 +614,21 @@ static void init_platform_timer(void)
 
     set_time_scale(&plt_scale, pts->frequency);
 
-    plt_overflow_period = scale_delta(
-        1ull << (pts->counter_bits-1), &plt_scale);
-    init_timer(&plt_overflow_timer, plt_overflow, NULL, 0);
-    plt_overflow(NULL);
+    if (pts->counter_bits != 64 )
+    {
+        plt_overflow_period = scale_delta(
+            1ull << (pts->counter_bits-1), &plt_scale);
+        init_timer(&plt_overflow_timer, plt_overflow, NULL, 0);
+        plt_overflow(NULL);
 
-    platform_timer_stamp = plt_stamp64;
+        platform_timer_stamp = plt_stamp64;
+    }
+    else
+    {
+        platform_timer_stamp =  stime_platform_stamp = 0;
+        plt_stamp = plt_stamp64 = 0;
+    }
+
 
     printk("Platform timer is %s %s\n",
            freq_string(pts->frequency), pts->name);
@@ -752,14 +751,19 @@ static unsigned long get_cmos_time(void)
 
 s_time_t get_s_time(void)
 {
-    struct cpu_time *t = &this_cpu(cpu_time);
+    struct cpu_time *t;
     u64 tsc, delta;
     s_time_t now;
 
     rdtscll(tsc);
-    delta = tsc - t->local_tsc_stamp;
-    now = t->stime_local_stamp + scale_delta(delta, &t->tsc_scale);
-
+    if (platform_timer_is_tsc() )
+        now = scale_delta(tsc, &plt_scale);
+    else
+    {
+        t = &this_cpu(cpu_time);
+        delta = tsc - t->local_tsc_stamp;
+        now = t->stime_local_stamp + scale_delta(delta, &t->tsc_scale);
+    }
     return now;
 }
 
@@ -821,10 +825,6 @@ int cpu_frequency_change(u64 freq)
 {
     struct cpu_time *t = &this_cpu(cpu_time);
     u64 curr_tsc;
-
-    /* Nothing to do if TSC is platform timer. Assume it is constant-rate. */
-    if ( platform_timer_is_tsc() )
-        return 0;
 
     /* Sanity check: CPU frequency allegedly dropping below 1MHz? */
     if ( freq < 1000000u )
@@ -1024,12 +1024,9 @@ void init_percpu_time(void)
     unsigned long flags;
     s_time_t now;
 
-    if ( platform_timer_is_tsc() )
-        return;
-
     local_irq_save(flags);
     rdtscll(t->local_tsc_stamp);
-    now = read_platform_stime();
+    now = ( !plt_src.read_counter ) ? 0 : read_platform_stime();
     local_irq_restore(flags);
 
     t->stime_master_stamp = now;
@@ -1047,10 +1044,10 @@ int __init init_xen_time(void)
 
     local_irq_disable();
 
+    init_percpu_time();
+
     stime_platform_stamp = 0;
     init_platform_timer();
-
-    init_percpu_time();
 
     /* check if TSC is invariant during deep C state
        this is a new feature introduced by Nehalem*/
@@ -1146,12 +1143,11 @@ int time_suspend(void)
 
 int time_resume(void)
 {
-    /*u64 tmp = */init_pit_and_calibrate_tsc();
+    u64 tmp = init_pit_and_calibrate_tsc();
 
     disable_pit_irq();
 
-    /* Disable this while calibrate_tsc_ap() also is skipped. */
-    /*set_time_scale(&this_cpu(cpu_time).tsc_scale, tmp);*/
+    set_time_scale(&this_cpu(cpu_time).tsc_scale, tmp);
 
     resume_platform_timer();