hw/ptimer: Perform counter wrap around if timer already expired

ptimer_get_count() might be called while QEMU timer already been expired.
In that case ptimer would return counter = 0, which might be undesirable
in case of polled timer. Do counter wrap around for periodic timer to keep
it distributed. In order to achieve more accurate emulation behaviour of
certain hardware, don't perform wrap around when in icount mode and return
counter = 0 in that case (that doesn't affect polled counter distribution).
Signed-off-by: NDmitry Osipenko <digetx@gmail.com>
Reviewed-by: NPeter Crosthwaite <crosthwaite.peter@gmail.com>
Message-id: 4ce381c7d24d85d165ff251d2875d16a4b6a5c04.1464367869.git.digetx@gmail.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/core/ptimer.c

@@ -84,14 +84,16 @@ static void ptimer_tick(void *opaque)
 
 uint64_t ptimer_get_count(ptimer_state *s)
 {
-    int64_t now;
     uint64_t counter;
 
     if (s->enabled) {
-        now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+        int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+        int64_t next = s->next_event;
+        bool expired = (now - next >= 0);
+        bool oneshot = (s->enabled == 2);
+
         /* Figure out the current counter value.  */
-        if (now - s->next_event > 0
-            || s->period == 0) {
+        if (s->period == 0 || (expired && (oneshot || use_icount))) {
             /* Prevent timer underflowing if it should already have
                triggered.  */
             counter = 0;
@@ -103,7 +105,7 @@ uint64_t ptimer_get_count(ptimer_state *s)
             uint32_t period_frac = s->period_frac;
             uint64_t period = s->period;
 
-            if ((s->enabled == 1) && !use_icount && (s->delta * period < 10000)) {
+            if (!oneshot && (s->delta * period < 10000) && !use_icount) {
                 period = 10000 / s->delta;
                 period_frac = 0;
             }
@@ -118,7 +120,7 @@ uint64_t ptimer_get_count(ptimer_state *s)
                backwards.
             */
 
-            rem = s->next_event - now;
+            rem = expired ? now - next : next - now;
             div = period;
 
             clz1 = clz64(rem);
@@ -138,6 +140,11 @@ uint64_t ptimer_get_count(ptimer_state *s)
                     div += 1;
             }
             counter = rem / div;
+
+            if (expired && counter != 0) {
+                /* Wrap around periodic counter.  */
+                counter = s->limit - (counter - 1) % s->limit;
+            }
         }
     } else {
         counter = s->delta;