[Qemu-devel] [PATCH v8 2/4] hw/ptimer: Perform tick and counter wrap around if timer already expired

[Dmitry Osipenko]

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 addition, there is no reason to keep expired timer tick deferred, so
just perform the tick from ptimer_get_count().

Signed-off-by: Dmitry Osipenko <dig...@gmail.com>
---
 hw/core/ptimer.c | 35 +++++++++++++++++++++++++++++------
 1 file changed, 29 insertions(+), 6 deletions(-)

diff --git a/hw/core/ptimer.c b/hw/core/ptimer.c
index 035af97..96a6c7a 100644
--- a/hw/core/ptimer.c
+++ b/hw/core/ptimer.c
@@ -85,15 +85,21 @@ static void ptimer_tick(void *opaque)
 
 uint64_t ptimer_get_count(ptimer_state *s)
 {
+    int enabled = s->enabled;
     int64_t now;
+    int64_t next;
     uint64_t counter;
+    int expired;
+    int oneshot;
 
-    if (s->enabled) {
+    if (enabled) {
         now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+        next = s->next_event;
+        expired = (now - next >= 0);
+        oneshot = (enabled == 2);
         /* Figure out the current counter value.  */
-        if (now - s->next_event > 0
-            || s->period == 0) {
-            /* Prevent timer underflowing if it should already have
+        if (s->period == 0 || (expired && oneshot)) {
+            /* Prevent one-shot timer underflowing if it should already have
                triggered.  */
             counter = 0;
         } else {
@@ -114,12 +120,12 @@ uint64_t ptimer_get_count(ptimer_state *s)
                backwards.
             */
 
-            if ((s->enabled == 1) && (s->limit * period < 10000)) {
+            if (!oneshot && (s->limit * period < 10000)) {
                 period = 10000 / s->limit;
                 period_frac = 0;
             }
 
-            rem = s->next_event - now;
+            rem = expired ? now - next : next - now;
             div = period;
 
             clz1 = clz64(rem);
@@ -139,6 +145,23 @@ uint64_t ptimer_get_count(ptimer_state *s)
                     div += 1;
             }
             counter = rem / div;
+
+            if (expired) {
+                /* Wrap around periodic counter.  */
+                counter = s->delta = s->limit - counter % s->limit;
+            }
+        }
+
+        if (expired) {
+            if (oneshot) {
+                ptimer_tick(s);
+            } else {
+                /* Don't use ptimer_tick() for the periodic timer since it
+                 * would reset the delta value.
+                 */
+                ptimer_trigger(s);
+                ptimer_reload(s);
+            }
         }
     } else {
         counter = s->delta;
-- 
2.6.4