hw/ptimer: Add "continuous trigger" policy

Currently, periodic timer that has load = delta = 0 performs trigger
on timer reload and stops, printing a "period zero" error message.
Introduce new policy that makes periodic timer to continuously trigger
with a period interval in case of load = 0.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Message-id: 632b23dd11055d9bd5e338d66b38fac0bd51462e.1475421224.git.digetx@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

2 files changed, 31 insertions, 3 deletions

diff --git a/hw/core/ptimer.c b/hw/core/ptimer.c
index 1f4122da4e..1aa019447f 100644
--- a/hw/core/ptimer.c
+++ b/hw/core/ptimer.c
@@ -47,7 +47,8 @@ static void ptimer_reload(ptimer_state *s, int delta_adjust)
         ptimer_trigger(s);
         delta = s->delta = s->limit;
     }
-    if (delta == 0 || s->period == 0) {
+
+    if (s->period == 0) {
         if (!qtest_enabled()) {
             fprintf(stderr, "Timer with period zero, disabling\n");
         }
@@ -60,6 +61,21 @@ static void ptimer_reload(ptimer_state *s, int delta_adjust)
         delta += delta_adjust;
     }
 
+    if (delta == 0 && (s->policy_mask & PTIMER_POLICY_CONTINUOUS_TRIGGER)) {
+        if (s->enabled == 1 && s->limit == 0) {
+            delta = 1;
+        }
+    }
+
+    if (delta == 0) {
+        if (!qtest_enabled()) {
+            fprintf(stderr, "Timer with delta zero, disabling\n");
+        }
+        timer_del(s->timer);
+        s->enabled = 0;
+        return;
+    }
+
     /*
      * Artificially limit timeout rate to something
      * achievable under QEMU.  Otherwise, QEMU spends all
@@ -90,7 +106,15 @@ static void ptimer_tick(void *opaque)
     if (s->enabled == 2) {
         s->enabled = 0;
     } else {
-        ptimer_reload(s, DELTA_ADJUST);
+        int delta_adjust = DELTA_ADJUST;
+
+        if (s->limit == 0) {
+            /* If a "continuous trigger" policy is not used and limit == 0,
+               we should error out.  */
+            delta_adjust = 0;
+        }
+
+        ptimer_reload(s, delta_adjust);
     }
 }
 
@@ -98,7 +122,7 @@ uint64_t ptimer_get_count(ptimer_state *s)
 {
     uint64_t counter;
 
-    if (s->enabled) {
+    if (s->enabled && s->delta != 0) {
         int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
         int64_t next = s->next_event;
         int64_t last = s->last_event;
diff --git a/include/hw/ptimer.h b/include/hw/ptimer.h
index 03441cbc22..b2fb4f9864 100644
--- a/include/hw/ptimer.h
+++ b/include/hw/ptimer.h
@@ -39,6 +39,10 @@
  * around.  */
 #define PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD (1 << 0)
 
+/* Running periodic timer that has counter = limit = 0 would continuously
+ * re-trigger every period.  */
+#define PTIMER_POLICY_CONTINUOUS_TRIGGER    (1 << 1)
+
 /* ptimer.c */
 typedef struct ptimer_state ptimer_state;
 typedef void (*ptimer_cb)(void *opaque);