hw/core/ptimer: Support ptimer being disabled by timer callback

In ptimer_reload(), we call the callback function provided by the
timer device that is using the ptimer.  This callback might disable
the ptimer.  The code mostly handles this correctly, except that
we'll still print the warning about "Timer with delta zero,
disabling" if the now-disabled timer happened to be set such that it
would fire again immediately if it were enabled (eg because the
limit/reload value is zero).

Suppress the spurious warning message and the unnecessary
repeat-deletion of the underlying timer in this case.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20201015151829.14656-2-peter.maydell@linaro.org

hw/core/ptimer.c

@@ -117,6 +117,10 @@ static void ptimer_reload(ptimer_state *s, int delta_adjust)
     }
 
     if (delta == 0) {
+        if (s->enabled == 0) {
+            /* trigger callback disabled the timer already */
+            return;
+        }
         if (!qtest_enabled()) {
             fprintf(stderr, "Timer with delta zero, disabling\n");
         }