[Qemu-devel] [PATCH] Revert "hw/ptimer: Perform counter wrap around if timer already expired"

[Qemu-devel] [PATCH] Revert "hw/ptimer: Perform counter wrap around if timer already expired"

[Dmitry Osipenko]

Software should see timer counter wraparound only after IRQ being triggered.
This fixes regression introduced by the commit 5a50307 ("hw/ptimer: Perform
counter wrap around if timer already expired"), resulting in monotonic timer
jumping backwards on SPARC emulated machine running NetBSD guest OS, as
reported by Mark Cave-Ayland.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
 hw/core/ptimer.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/hw/core/ptimer.c b/hw/core/ptimer.c
index 05b0c27..30829ee 100644
--- a/hw/core/ptimer.c
+++ b/hw/core/ptimer.c
@@ -93,7 +93,7 @@ uint64_t ptimer_get_count(ptimer_state *s)
         bool oneshot = (s->enabled == 2);
 
         /* Figure out the current counter value.  */
-        if (s->period == 0 || (expired && (oneshot || use_icount))) {
+        if (expired) {
             /* Prevent timer underflowing if it should already have
                triggered.  */
             counter = 0;
@@ -120,7 +120,7 @@ uint64_t ptimer_get_count(ptimer_state *s)
                backwards.
             */
 
-            rem = expired ? now - next : next - now;
+            rem = next - now;
             div = period;
 
             clz1 = clz64(rem);
@@ -140,11 +140,6 @@ uint64_t ptimer_get_count(ptimer_state *s)
                     div += 1;
             }
             counter = rem / div;
-
-            if (expired && counter != 0) {
-                /* Wrap around periodic counter.  */
-                counter = s->limit - (counter - 1) % s->limit;
-            }
         }
     } else {
         counter = s->delta;
-- 
2.9.0

Re: [Qemu-devel] [PATCH] Revert "hw/ptimer: Perform counter wrap around if timer already expired"

[Peter Maydell]

On 8 July 2016 at 14:22, Dmitry Osipenko <digetx@gmail.com> wrote:
> Software should see timer counter wraparound only after IRQ being triggered.
> This fixes regression introduced by the commit 5a50307 ("hw/ptimer: Perform
> counter wrap around if timer already expired"), resulting in monotonic timer
> jumping backwards on SPARC emulated machine running NetBSD guest OS, as
> reported by Mark Cave-Ayland.
>
> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> ---
>  hw/core/ptimer.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
>



Applied to target-arm.next, thanks.

-- PMM