[Qemu-devel] [PATCH v6] timer: a9gtimer: remove loop to auto-increment comparator

[P J P <ppandit@redhat.com>]

From: Prasad J Pandit <pjp@fedoraproject.org>

ARM A9MP processor has a peripheral timer with an auto-increment
register, which holds an increment step value. A user could set
this value to zero. When auto-increment control bit is enabled,
it leads to an infinite loop in 'a9_gtimer_update' while
updating comparator value. Remove this loop incrementing the
comparator value.

Reported-by: Li Qiang <liqiang6-s@360.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/timer/a9gtimer.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

Update per
  -> https://lists.gnu.org/archive/html/qemu-devel/2016-10/msg02891.html

diff --git a/hw/timer/a9gtimer.c b/hw/timer/a9gtimer.c
index 772f85f..03dfaf2 100644
--- a/hw/timer/a9gtimer.c
+++ b/hw/timer/a9gtimer.c
@@ -73,6 +73,7 @@ static void a9_gtimer_update(A9GTimerState *s, bool sync)
 
     A9GTimerUpdate update = a9_gtimer_get_update(s);
     int i;
+    uint64_t inc;
     int64_t next_cdiff = 0;
 
     for (i = 0; i < s->num_cpu; ++i) {
@@ -82,15 +83,15 @@ static void a9_gtimer_update(A9GTimerState *s, bool sync)
         if ((s->control & R_CONTROL_TIMER_ENABLE) &&
                 (gtb->control & R_CONTROL_COMP_ENABLE)) {
             /* R2p0+, where the compare function is >= */
-            while (gtb->compare < update.new) {
+            if (gtb->compare < update.new) {
                 DB_PRINT("Compare event happened for CPU %d\n", i);
                 gtb->status = 1;
-                if (gtb->control & R_CONTROL_AUTO_INCREMENT) {
-                    DB_PRINT("Auto incrementing timer compare by %" PRId32 "\n",
-                             gtb->inc);
-                    gtb->compare += gtb->inc;
-                } else {
-                    break;
+                if (gtb->control & R_CONTROL_AUTO_INCREMENT && gtb->inc) {
+                    inc = update.new + gtb->inc - gtb->compare - 1;
+                    inc = QEMU_ALIGN_DOWN(inc, gtb->inc);
+                    DB_PRINT("Auto incrementing timer compare by %"
+                                                        PRId64 "\n", inc);
+                    gtb->compare += inc;
                 }
             }
             cdiff = (int64_t)gtb->compare - (int64_t)update.new + 1;
-- 
2.5.5