mips: Expire late timers when reading cp0_count

When reading cp0_count from a timer with a late trigger that should
already have expired, expire it and raise the timer irq.

This makes it possible for guest code (e.g, Linux) that first read
cp0_count, then compare it with cp0_compare and check for raised
timer interrupt lines to run reliably.

Acked-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/hw/mips_timer.c b/hw/mips_timer.c
index 8c3208754..9c95f282a 100644
--- a/hw/mips_timer.c
+++ b/hw/mips_timer.c
@@ -69,9 +69,17 @@ uint32_t cpu_mips_get_count (CPUState *env)
     if (env->CP0_Cause & (1 << CP0Ca_DC)) {
         return env->CP0_Count;
     } else {
+        uint64_t now;
+
+        now = qemu_get_clock(vm_clock);
+        if (qemu_timer_pending(env->timer)
+            && qemu_timer_expired(env->timer, now)) {
+            /* The timer has already expired.  */
+            cpu_mips_timer_expire(env);
+        }
+
         return env->CP0_Count +
-            (uint32_t)muldiv64(qemu_get_clock(vm_clock),
-                               TIMER_FREQ, get_ticks_per_sec());
+            (uint32_t)muldiv64(now, TIMER_FREQ, get_ticks_per_sec());
     }
 }