x86: Reintroduce clocksource=tsc.

Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

xen/arch/x86/time.c

@@ -480,6 +480,35 @@ static int init_pmtimer(struct platform_timesource *pts)
     return 1;
 }
 
+/************************************************************
+ * PLATFORM TIMER 5: TSC
+ */
+
+static const char plt_tsc_name[] = "TSC";
+#define platform_timer_is_tsc() (plt_src.name == plt_tsc_name)
+
+static int init_tsctimer(struct platform_timesource *pts)
+{
+    if ( !tsc_invariant )
+        return 0;
+
+    pts->name = (char *)plt_tsc_name;
+    return 1;
+}
+
+static void make_tsctimer_record(void)
+{
+    struct cpu_time *t = &this_cpu(cpu_time);
+    s_time_t now;
+    u64 tsc;
+
+    rdtscll(tsc);
+    now = scale_delta(tsc, &t->tsc_scale);
+
+    t->local_tsc_stamp = tsc;
+    t->stime_local_stamp = t->stime_master_stamp = now;
+}
+
 /************************************************************
  * GENERIC PLATFORM TIMER INFRASTRUCTURE
  */
@@ -545,6 +574,12 @@ static void platform_time_calibration(void)
 
 static void resume_platform_timer(void)
 {
+    if ( platform_timer_is_tsc() )
+    {
+        /* TODO: Save/restore TSC values. */
+        return;
+    }
+
     /* No change in platform_stime across suspend/resume. */
     platform_timer_stamp = plt_stamp64;
     plt_stamp = plt_src.read_counter();
@@ -565,6 +600,8 @@ static void init_platform_timer(void)
             rc = init_cyclone(pts);
         else if ( !strcmp(opt_clocksource, "acpi") )
             rc = init_pmtimer(pts);
+        else if ( !strcmp(opt_clocksource, "tsc") )
+            rc = init_tsctimer(pts);
 
         if ( rc <= 0 )
             printk("WARNING: %s clocksource '%s'.\n",
@@ -578,6 +615,12 @@ static void init_platform_timer(void)
          !init_pmtimer(pts) )
         init_pit(pts);
 
+    if ( platform_timer_is_tsc() )
+    {
+        printk("Platform timer is TSC\n");
+        return;
+    }
+
     plt_mask = (u64)~0ull >> (64 - pts->counter_bits);
 
     set_time_scale(&plt_scale, pts->frequency);
@@ -780,6 +823,10 @@ 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 )
     {
@@ -861,6 +908,14 @@ static void local_time_calibration(void *unused)
     /* The overall calibration scale multiplier. */
     u32 calibration_mul_frac;
 
+    if ( platform_timer_is_tsc() )
+    {
+        make_tsctimer_record(); 
+        update_vcpu_system_time(current);
+        set_timer(&t->calibration_timer, NOW() + MILLISECS(10*1000));
+        return;
+    }
+
     prev_tsc          = t->local_tsc_stamp;
     prev_local_stime  = t->stime_local_stamp;
     prev_master_stime = t->stime_master_stamp;
@@ -978,6 +1033,12 @@ void init_percpu_time(void)
     unsigned long flags;
     s_time_t now;
 
+    if ( platform_timer_is_tsc() )
+    {
+        make_tsctimer_record();
+        goto out;
+    }
+
     local_irq_save(flags);
     rdtscll(t->local_tsc_stamp);
     now = !plt_src.read_counter ? 0 : read_platform_stime();
@@ -986,6 +1047,7 @@ void init_percpu_time(void)
     t->stime_master_stamp = now;
     t->stime_local_stamp  = now;
 
+ out:
     init_timer(&t->calibration_timer, local_time_calibration,
                NULL, smp_processor_id());
     set_timer(&t->calibration_timer, NOW() + EPOCH);
@@ -994,19 +1056,19 @@ void init_percpu_time(void)
 /* Late init function (after all CPUs are booted). */
 int __init init_xen_time(void)
 {
-    wc_sec = get_cmos_time();
-
     local_irq_disable();
 
+    /* check if TSC is invariant during deep C state
+       this is a new feature introduced by Nehalem*/
+    if ( cpuid_edx(0x80000007) & (1u<<8) )
+        tsc_invariant = 1;
+
     init_percpu_time();
 
     stime_platform_stamp = 0;
     init_platform_timer();
 
-    /* check if TSC is invariant during deep C state
-       this is a new feature introduced by Nehalem*/
-    if ( cpuid_edx(0x80000007) & (1U<<8) )
-        tsc_invariant = 1;
+    do_settime(get_cmos_time(), 0, NOW());
 
     local_irq_enable();
 
@@ -1120,10 +1182,10 @@ int time_resume(void)
 
     resume_platform_timer();
 
-    do_settime(get_cmos_time() + cmos_utc_offset, 0, read_platform_stime());
-
     init_percpu_time();
 
+    do_settime(get_cmos_time() + cmos_utc_offset, 0, NOW());
+
     if ( !is_idle_vcpu(current) )
         update_vcpu_system_time(current);