diff mbox

[v14,1/3] hw/ptimer: Support running with counter = 0 by introducing new policy feature

Message ID 2bbc3737669523d9483f27276f929a6c4772fd48.1466167530.git.digetx@gmail.com
State New
Headers show

Commit Message

Dmitry Osipenko June 17, 2016, 1:17 p.m. UTC
Currently ptimer prints error message and stops the running timer that has
delta (counter) = 0, this is an incorrect behaviour for some of the ptimer
users. There are different variants of how particular timer could handle that
case besides stopping the timer, like immediate or deferred IRQ trigger.
Introduce policy feature that provides ptimer with an information about the
correct behaviour.

Implement the "counter = 0 triggers IRQ after one period" policy, as it is
known to be used by the ARM MPTimer and set "default" policy to all ptimer
users, maintaining old behaviour till they get fixed.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
 hw/arm/musicpal.c            |  2 +-
 hw/core/ptimer.c             | 45 +++++++++++++++++++++++---------------------
 hw/dma/xilinx_axidma.c       |  2 +-
 hw/m68k/mcf5206.c            |  2 +-
 hw/m68k/mcf5208.c            |  2 +-
 hw/net/fsl_etsec/etsec.c     |  2 +-
 hw/net/lan9118.c             |  2 +-
 hw/timer/allwinner-a10-pit.c |  2 +-
 hw/timer/arm_timer.c         |  2 +-
 hw/timer/aspeed_timer.c      |  2 +-
 hw/timer/digic-timer.c       |  2 +-
 hw/timer/etraxfs_timer.c     |  6 +++---
 hw/timer/exynos4210_mct.c    |  7 ++++---
 hw/timer/exynos4210_pwm.c    |  2 +-
 hw/timer/exynos4210_rtc.c    |  4 ++--
 hw/timer/grlib_gptimer.c     |  2 +-
 hw/timer/imx_epit.c          |  4 ++--
 hw/timer/imx_gpt.c           |  2 +-
 hw/timer/lm32_timer.c        |  2 +-
 hw/timer/milkymist-sysctl.c  |  4 ++--
 hw/timer/puv3_ost.c          |  2 +-
 hw/timer/sh_timer.c          |  2 +-
 hw/timer/slavio_timer.c      |  2 +-
 hw/timer/xilinx_timer.c      |  2 +-
 include/hw/ptimer.h          |  7 ++++++-
 25 files changed, 61 insertions(+), 52 deletions(-)

Comments

Peter Maydell June 23, 2016, 1:49 p.m. UTC | #1
On 17 June 2016 at 14:17, Dmitry Osipenko <digetx@gmail.com> wrote:
> Currently ptimer prints error message and stops the running timer that has
> delta (counter) = 0, this is an incorrect behaviour for some of the ptimer
> users. There are different variants of how particular timer could handle that
> case besides stopping the timer, like immediate or deferred IRQ trigger.
> Introduce policy feature that provides ptimer with an information about the
> correct behaviour.
>
> Implement the "counter = 0 triggers IRQ after one period" policy, as it is
> known to be used by the ARM MPTimer and set "default" policy to all ptimer
> users, maintaining old behaviour till they get fixed.

Could you split this into:
 (1) a patch which just adds the new argument to ptimer_init() and
     updates all its callers
 (2) a patch which adds support for setting the policy option to
     something other than the default value

and also make sure that we only do one change per patch -- there
seem to be several different behaviour changes tangled up in
one patch here.

I think that will be easier to review.

> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>

> diff --git a/hw/core/ptimer.c b/hw/core/ptimer.c
> index 05b0c27..289e23e 100644
> --- a/hw/core/ptimer.c
> +++ b/hw/core/ptimer.c
> @@ -21,6 +21,7 @@ struct ptimer_state
>      int64_t period;
>      int64_t last_event;
>      int64_t next_event;
> +    uint8_t policy_mask;
>      QEMUBH *bh;
>      QEMUTimer *timer;
>  };
> @@ -35,14 +36,15 @@ static void ptimer_trigger(ptimer_state *s)
>
>  static void ptimer_reload(ptimer_state *s)
>  {
> -    uint32_t period_frac = s->period_frac;
> +    int64_t period_frac = s->period_frac;

Why does this variable change type?

>      uint64_t period = s->period;
> +    uint64_t delta = s->delta;
>
> -    if (s->delta == 0) {
> -        ptimer_trigger(s);
> -        s->delta = s->limit;
> +    if (delta == 0 && (s->policy_mask & PTIMER_POLICY_CNT_0_DEFERRED_TRIG)) {
> +        delta = 1;
>      }
> -    if (s->delta == 0 || s->period == 0) {
> +
> +    if (delta == 0 || period == 0) {
>          fprintf(stderr, "Timer with period zero, disabling\n");
>          s->enabled = 0;
>          return;
> @@ -57,15 +59,15 @@ static void ptimer_reload(ptimer_state *s)
>       * on the current generation of host machines.
>       */
>
> -    if (s->enabled == 1 && (s->delta * period < 10000) && !use_icount) {
> -        period = 10000 / s->delta;
> +    if (s->enabled == 1 && (delta * period < 10000) && !use_icount) {
> +        period = 10000 / delta;
>          period_frac = 0;
>      }
>
>      s->last_event = s->next_event;
> -    s->next_event = s->last_event + s->delta * period;
> +    s->next_event = s->last_event + delta * period;
>      if (period_frac) {
> -        s->next_event += ((int64_t)period_frac * s->delta) >> 32;
> +        s->next_event += (period_frac * delta) >> 32;
>      }
>      timer_mod(s->timer, s->next_event);
>  }
> @@ -73,27 +75,30 @@ static void ptimer_reload(ptimer_state *s)
>  static void ptimer_tick(void *opaque)
>  {
>      ptimer_state *s = (ptimer_state *)opaque;
> -    ptimer_trigger(s);
> -    s->delta = 0;
> -    if (s->enabled == 2) {
> +
> +    s->delta = (s->enabled == 1) ? s->limit : 0;
> +
> +    if (s->delta == 0) {

This seems to be a change not guarded by a check of a policy bit?

>          s->enabled = 0;
>      } else {
>          ptimer_reload(s);
>      }
> +
> +    ptimer_trigger(s);
>  }
>
>  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;
>          bool expired = (now - next >= 0);
>          bool oneshot = (s->enabled == 2);
>
>          /* Figure out the current counter value.  */
> -        if (s->period == 0 || (expired && (oneshot || use_icount))) {
> +        if (expired && (oneshot || use_icount)) {
>              /* Prevent timer underflowing if it should already have
>                 triggered.  */
>              counter = 0;
> @@ -165,10 +170,6 @@ void ptimer_run(ptimer_state *s, int oneshot)
>  {
>      bool was_disabled = !s->enabled;
>
> -    if (was_disabled && s->period == 0) {
> -        fprintf(stderr, "Timer with period zero, disabling\n");
> -        return;
> -    }

If the default policy value was provided, we shouldn't change behaviour.

>      s->enabled = oneshot ? 2 : 1;
>      if (was_disabled) {
>          s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
> @@ -203,6 +204,7 @@ void ptimer_set_period(ptimer_state *s, int64_t period)
>  /* Set counter frequency in Hz.  */
>  void ptimer_set_freq(ptimer_state *s, uint32_t freq)
>  {
> +    g_assert(freq != 0 && freq <= 1000000000ll);

This seems to be an unrelated change.

>      s->delta = ptimer_get_count(s);
>      s->period = 1000000000ll / freq;
>      s->period_frac = (1000000000ll << 32) / freq;
> @@ -232,8 +234,8 @@ uint64_t ptimer_get_limit(ptimer_state *s)
>
>  const VMStateDescription vmstate_ptimer = {
>      .name = "ptimer",
> -    .version_id = 1,
> -    .minimum_version_id = 1,
> +    .version_id = 2,
> +    .minimum_version_id = 2,

Why are we bumping the version ID here?

>      .fields = (VMStateField[]) {
>          VMSTATE_UINT8(enabled, ptimer_state),
>          VMSTATE_UINT64(limit, ptimer_state),
> @@ -247,12 +249,13 @@ const VMStateDescription vmstate_ptimer = {
>      }
>  };
>
> -ptimer_state *ptimer_init(QEMUBH *bh)
> +ptimer_state *ptimer_init(QEMUBH *bh, uint8_t policy_mask)
>  {
>      ptimer_state *s;
>
>      s = (ptimer_state *)g_malloc0(sizeof(ptimer_state));
>      s->bh = bh;
>      s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, ptimer_tick, s);
> +    s->policy_mask = policy_mask;
>      return s;
>  }

thanks
-- PMM
Dmitry Osipenko June 23, 2016, 4:32 p.m. UTC | #2
On 23.06.2016 16:49, Peter Maydell wrote:
> On 17 June 2016 at 14:17, Dmitry Osipenko <digetx@gmail.com> wrote:
>> Currently ptimer prints error message and stops the running timer that has
>> delta (counter) = 0, this is an incorrect behaviour for some of the ptimer
>> users. There are different variants of how particular timer could handle that
>> case besides stopping the timer, like immediate or deferred IRQ trigger.
>> Introduce policy feature that provides ptimer with an information about the
>> correct behaviour.
>>
>> Implement the "counter = 0 triggers IRQ after one period" policy, as it is
>> known to be used by the ARM MPTimer and set "default" policy to all ptimer
>> users, maintaining old behaviour till they get fixed.
> 
> Could you split this into:
>  (1) a patch which just adds the new argument to ptimer_init() and
>      updates all its callers
>  (2) a patch which adds support for setting the policy option to
>      something other than the default value
> 
> and also make sure that we only do one change per patch -- there
> seem to be several different behaviour changes tangled up in
> one patch here.
> 
> I think that will be easier to review.
> 

This patch isn't supposed to change behaviour for any of the current timers. I
think it is clearly expressed in the last sentence of the commit message. There
is one unintended behaviour change in this patch, it's my overlook [see below].

>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> 
>> diff --git a/hw/core/ptimer.c b/hw/core/ptimer.c
>> index 05b0c27..289e23e 100644
>> --- a/hw/core/ptimer.c
>> +++ b/hw/core/ptimer.c
>> @@ -21,6 +21,7 @@ struct ptimer_state
>>      int64_t period;
>>      int64_t last_event;
>>      int64_t next_event;
>> +    uint8_t policy_mask;
>>      QEMUBH *bh;
>>      QEMUTimer *timer;
>>  };
>> @@ -35,14 +36,15 @@ static void ptimer_trigger(ptimer_state *s)
>>
>>  static void ptimer_reload(ptimer_state *s)
>>  {
>> -    uint32_t period_frac = s->period_frac;
>> +    int64_t period_frac = s->period_frac;
> 
> Why does this variable change type?
> 

I removed the in-place type conversion further:
>>      if (period_frac) {
>> -        s->next_event += ((int64_t)period_frac * s->delta) >> 32;
>> +        s->next_event += (period_frac * delta) >> 32;
>>      }
>>      timer_mod(s->timer, s->next_event);
>>  }
>> @@ -73,27 +75,30 @@ static void ptimer_reload(ptimer_state *s)
>>  static void ptimer_tick(void *opaque)
>>  {
>>      ptimer_state *s = (ptimer_state *)opaque;
>> -    ptimer_trigger(s);
>> -    s->delta = 0;
>> -    if (s->enabled == 2) {
>> +
>> +    s->delta = (s->enabled == 1) ? s->limit : 0;
>> +
>> +    if (s->delta == 0) {
> 
> This seems to be a change not guarded by a check of a policy bit?
> 

That's a good question. In the current ARM MPTimer conversion patch, I assume
that delta = 0 would stop the timer regardless of it's mode and ptimer user
would itself re-arm timer in a tick() handler if needed. However, after your
question, I think it's a bit unintuitive and needs to be changed to continuous
*ptimer* trigger in periodic mode in case of the deferred trigger policy.

>>          s->enabled = 0;
>>      } else {
>>          ptimer_reload(s);
>>      }
>> +
>> +    ptimer_trigger(s);
>>  }
>>
>>  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;
>>          bool expired = (now - next >= 0);
>>          bool oneshot = (s->enabled == 2);
>>
>>          /* Figure out the current counter value.  */
>> -        if (s->period == 0 || (expired && (oneshot || use_icount))) {
>> +        if (expired && (oneshot || use_icount)) {
>>              /* Prevent timer underflowing if it should already have
>>                 triggered.  */
>>              counter = 0;
>> @@ -165,10 +170,6 @@ void ptimer_run(ptimer_state *s, int oneshot)
>>  {
>>      bool was_disabled = !s->enabled;
>>
>> -    if (was_disabled && s->period == 0) {
>> -        fprintf(stderr, "Timer with period zero, disabling\n");
>> -        return;
>> -    }
> 
> If the default policy value was provided, we shouldn't change behaviour.
> 

Right, now I see that ptimer_trigger() is missed in case of running timer with a
default policy and delta = 0. Thanks for the note, will fix it. I'll craft
QTests for the ptimer, shouldn't take a lot of effort.

>>      s->enabled = oneshot ? 2 : 1;
>>      if (was_disabled) {
>>          s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
>> @@ -203,6 +204,7 @@ void ptimer_set_period(ptimer_state *s, int64_t period)
>>  /* Set counter frequency in Hz.  */
>>  void ptimer_set_freq(ptimer_state *s, uint32_t freq)
>>  {
>> +    g_assert(freq != 0 && freq <= 1000000000ll);
> 
> This seems to be an unrelated change.
> 

Agree :) I have hit it couple times during the work on the ARM MPTimer patch in
the past, decided that it may not worth a whole patch for a such simple one-liner.

>>      s->delta = ptimer_get_count(s);
>>      s->period = 1000000000ll / freq;
>>      s->period_frac = (1000000000ll << 32) / freq;
>> @@ -232,8 +234,8 @@ uint64_t ptimer_get_limit(ptimer_state *s)
>>
>>  const VMStateDescription vmstate_ptimer = {
>>      .name = "ptimer",
>> -    .version_id = 1,
>> -    .minimum_version_id = 1,
>> +    .version_id = 2,
>> +    .minimum_version_id = 2,
> 
> Why are we bumping the version ID here?
> 

Ooops, good catch!

Thanks for the review!
Peter Maydell June 23, 2016, 4:43 p.m. UTC | #3
On 23 June 2016 at 17:32, Dmitry Osipenko <digetx@gmail.com> wrote:
> On 23.06.2016 16:49, Peter Maydell wrote:
>> On 17 June 2016 at 14:17, Dmitry Osipenko <digetx@gmail.com> wrote:
>>> Currently ptimer prints error message and stops the running timer that has
>>> delta (counter) = 0, this is an incorrect behaviour for some of the ptimer
>>> users. There are different variants of how particular timer could handle that
>>> case besides stopping the timer, like immediate or deferred IRQ trigger.
>>> Introduce policy feature that provides ptimer with an information about the
>>> correct behaviour.
>>>
>>> Implement the "counter = 0 triggers IRQ after one period" policy, as it is
>>> known to be used by the ARM MPTimer and set "default" policy to all ptimer
>>> users, maintaining old behaviour till they get fixed.
>>
>> Could you split this into:
>>  (1) a patch which just adds the new argument to ptimer_init() and
>>      updates all its callers
>>  (2) a patch which adds support for setting the policy option to
>>      something other than the default value
>>
>> and also make sure that we only do one change per patch -- there
>> seem to be several different behaviour changes tangled up in
>> one patch here.
>>
>> I think that will be easier to review.
>>
>
> This patch isn't supposed to change behaviour for any of the current timers. I
> think it is clearly expressed in the last sentence of the commit message. There
> is one unintended behaviour change in this patch, it's my overlook [see below].

Right, but my point is that it is hard to tell that when I read
the patch to review it, and splitting this will make it easier.

thanks
-- PMM
Dmitry Osipenko June 23, 2016, 5:05 p.m. UTC | #4
On 23.06.2016 19:43, Peter Maydell wrote:
> On 23 June 2016 at 17:32, Dmitry Osipenko <digetx@gmail.com> wrote:
>> On 23.06.2016 16:49, Peter Maydell wrote:
>>> On 17 June 2016 at 14:17, Dmitry Osipenko <digetx@gmail.com> wrote:
>>>> Currently ptimer prints error message and stops the running timer that has
>>>> delta (counter) = 0, this is an incorrect behaviour for some of the ptimer
>>>> users. There are different variants of how particular timer could handle that
>>>> case besides stopping the timer, like immediate or deferred IRQ trigger.
>>>> Introduce policy feature that provides ptimer with an information about the
>>>> correct behaviour.
>>>>
>>>> Implement the "counter = 0 triggers IRQ after one period" policy, as it is
>>>> known to be used by the ARM MPTimer and set "default" policy to all ptimer
>>>> users, maintaining old behaviour till they get fixed.
>>>
>>> Could you split this into:
>>>  (1) a patch which just adds the new argument to ptimer_init() and
>>>      updates all its callers
>>>  (2) a patch which adds support for setting the policy option to
>>>      something other than the default value
>>>
>>> and also make sure that we only do one change per patch -- there
>>> seem to be several different behaviour changes tangled up in
>>> one patch here.
>>>
>>> I think that will be easier to review.
>>>
>>
>> This patch isn't supposed to change behaviour for any of the current timers. I
>> think it is clearly expressed in the last sentence of the commit message. There
>> is one unintended behaviour change in this patch, it's my overlook [see below].
> 
> Right, but my point is that it is hard to tell that when I read
> the patch to review it, and splitting this will make it easier.
> 
> thanks
> -- PMM
> 

Ah, you are meaning to derive adding *new* "deferred trigger" policy into a
separate patch. I'll do it.
diff mbox

Patch

diff --git a/hw/arm/musicpal.c b/hw/arm/musicpal.c
index 7a4cc07..087696a 100644
--- a/hw/arm/musicpal.c
+++ b/hw/arm/musicpal.c
@@ -837,7 +837,7 @@  static void mv88w8618_timer_init(SysBusDevice *dev, mv88w8618_timer_state *s,
     s->freq = freq;
 
     bh = qemu_bh_new(mv88w8618_timer_tick, s);
-    s->ptimer = ptimer_init(bh);
+    s->ptimer = ptimer_init(bh, PTIMER_POLICY_DEFAULT);
 }
 
 static uint64_t mv88w8618_pit_read(void *opaque, hwaddr offset,
diff --git a/hw/core/ptimer.c b/hw/core/ptimer.c
index 05b0c27..289e23e 100644
--- a/hw/core/ptimer.c
+++ b/hw/core/ptimer.c
@@ -21,6 +21,7 @@  struct ptimer_state
     int64_t period;
     int64_t last_event;
     int64_t next_event;
+    uint8_t policy_mask;
     QEMUBH *bh;
     QEMUTimer *timer;
 };
@@ -35,14 +36,15 @@  static void ptimer_trigger(ptimer_state *s)
 
 static void ptimer_reload(ptimer_state *s)
 {
-    uint32_t period_frac = s->period_frac;
+    int64_t period_frac = s->period_frac;
     uint64_t period = s->period;
+    uint64_t delta = s->delta;
 
-    if (s->delta == 0) {
-        ptimer_trigger(s);
-        s->delta = s->limit;
+    if (delta == 0 && (s->policy_mask & PTIMER_POLICY_CNT_0_DEFERRED_TRIG)) {
+        delta = 1;
     }
-    if (s->delta == 0 || s->period == 0) {
+
+    if (delta == 0 || period == 0) {
         fprintf(stderr, "Timer with period zero, disabling\n");
         s->enabled = 0;
         return;
@@ -57,15 +59,15 @@  static void ptimer_reload(ptimer_state *s)
      * on the current generation of host machines.
      */
 
-    if (s->enabled == 1 && (s->delta * period < 10000) && !use_icount) {
-        period = 10000 / s->delta;
+    if (s->enabled == 1 && (delta * period < 10000) && !use_icount) {
+        period = 10000 / delta;
         period_frac = 0;
     }
 
     s->last_event = s->next_event;
-    s->next_event = s->last_event + s->delta * period;
+    s->next_event = s->last_event + delta * period;
     if (period_frac) {
-        s->next_event += ((int64_t)period_frac * s->delta) >> 32;
+        s->next_event += (period_frac * delta) >> 32;
     }
     timer_mod(s->timer, s->next_event);
 }
@@ -73,27 +75,30 @@  static void ptimer_reload(ptimer_state *s)
 static void ptimer_tick(void *opaque)
 {
     ptimer_state *s = (ptimer_state *)opaque;
-    ptimer_trigger(s);
-    s->delta = 0;
-    if (s->enabled == 2) {
+
+    s->delta = (s->enabled == 1) ? s->limit : 0;
+
+    if (s->delta == 0) {
         s->enabled = 0;
     } else {
         ptimer_reload(s);
     }
+
+    ptimer_trigger(s);
 }
 
 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;
         bool expired = (now - next >= 0);
         bool oneshot = (s->enabled == 2);
 
         /* Figure out the current counter value.  */
-        if (s->period == 0 || (expired && (oneshot || use_icount))) {
+        if (expired && (oneshot || use_icount)) {
             /* Prevent timer underflowing if it should already have
                triggered.  */
             counter = 0;
@@ -165,10 +170,6 @@  void ptimer_run(ptimer_state *s, int oneshot)
 {
     bool was_disabled = !s->enabled;
 
-    if (was_disabled && s->period == 0) {
-        fprintf(stderr, "Timer with period zero, disabling\n");
-        return;
-    }
     s->enabled = oneshot ? 2 : 1;
     if (was_disabled) {
         s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
@@ -203,6 +204,7 @@  void ptimer_set_period(ptimer_state *s, int64_t period)
 /* Set counter frequency in Hz.  */
 void ptimer_set_freq(ptimer_state *s, uint32_t freq)
 {
+    g_assert(freq != 0 && freq <= 1000000000ll);
     s->delta = ptimer_get_count(s);
     s->period = 1000000000ll / freq;
     s->period_frac = (1000000000ll << 32) / freq;
@@ -232,8 +234,8 @@  uint64_t ptimer_get_limit(ptimer_state *s)
 
 const VMStateDescription vmstate_ptimer = {
     .name = "ptimer",
-    .version_id = 1,
-    .minimum_version_id = 1,
+    .version_id = 2,
+    .minimum_version_id = 2,
     .fields = (VMStateField[]) {
         VMSTATE_UINT8(enabled, ptimer_state),
         VMSTATE_UINT64(limit, ptimer_state),
@@ -247,12 +249,13 @@  const VMStateDescription vmstate_ptimer = {
     }
 };
 
-ptimer_state *ptimer_init(QEMUBH *bh)
+ptimer_state *ptimer_init(QEMUBH *bh, uint8_t policy_mask)
 {
     ptimer_state *s;
 
     s = (ptimer_state *)g_malloc0(sizeof(ptimer_state));
     s->bh = bh;
     s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, ptimer_tick, s);
+    s->policy_mask = policy_mask;
     return s;
 }
diff --git a/hw/dma/xilinx_axidma.c b/hw/dma/xilinx_axidma.c
index a4753e5..b135a5f 100644
--- a/hw/dma/xilinx_axidma.c
+++ b/hw/dma/xilinx_axidma.c
@@ -548,7 +548,7 @@  static void xilinx_axidma_realize(DeviceState *dev, Error **errp)
 
         st->nr = i;
         st->bh = qemu_bh_new(timer_hit, st);
-        st->ptimer = ptimer_init(st->bh);
+        st->ptimer = ptimer_init(st->bh, PTIMER_POLICY_DEFAULT);
         ptimer_set_freq(st->ptimer, s->freqhz);
     }
     return;
diff --git a/hw/m68k/mcf5206.c b/hw/m68k/mcf5206.c
index e14896e..b81901f 100644
--- a/hw/m68k/mcf5206.c
+++ b/hw/m68k/mcf5206.c
@@ -139,7 +139,7 @@  static m5206_timer_state *m5206_timer_init(qemu_irq irq)
 
     s = (m5206_timer_state *)g_malloc0(sizeof(m5206_timer_state));
     bh = qemu_bh_new(m5206_timer_trigger, s);
-    s->timer = ptimer_init(bh);
+    s->timer = ptimer_init(bh, PTIMER_POLICY_DEFAULT);
     s->irq = irq;
     m5206_timer_reset(s);
     return s;
diff --git a/hw/m68k/mcf5208.c b/hw/m68k/mcf5208.c
index 2415557..9240ebf 100644
--- a/hw/m68k/mcf5208.c
+++ b/hw/m68k/mcf5208.c
@@ -183,7 +183,7 @@  static void mcf5208_sys_init(MemoryRegion *address_space, qemu_irq *pic)
     for (i = 0; i < 2; i++) {
         s = (m5208_timer_state *)g_malloc0(sizeof(m5208_timer_state));
         bh = qemu_bh_new(m5208_timer_trigger, s);
-        s->timer = ptimer_init(bh);
+        s->timer = ptimer_init(bh, PTIMER_POLICY_DEFAULT);
         memory_region_init_io(&s->iomem, NULL, &m5208_timer_ops, s,
                               "m5208-timer", 0x00004000);
         memory_region_add_subregion(address_space, 0xfc080000 + 0x4000 * i,
diff --git a/hw/net/fsl_etsec/etsec.c b/hw/net/fsl_etsec/etsec.c
index 98250e0..8f640b0 100644
--- a/hw/net/fsl_etsec/etsec.c
+++ b/hw/net/fsl_etsec/etsec.c
@@ -387,7 +387,7 @@  static void etsec_realize(DeviceState *dev, Error **errp)
 
 
     etsec->bh     = qemu_bh_new(etsec_timer_hit, etsec);
-    etsec->ptimer = ptimer_init(etsec->bh);
+    etsec->ptimer = ptimer_init(etsec->bh, PTIMER_POLICY_DEFAULT);
     ptimer_set_freq(etsec->ptimer, 100);
 }
 
diff --git a/hw/net/lan9118.c b/hw/net/lan9118.c
index 2052073..650a6c7 100644
--- a/hw/net/lan9118.c
+++ b/hw/net/lan9118.c
@@ -1345,7 +1345,7 @@  static int lan9118_init1(SysBusDevice *sbd)
     s->txp = &s->tx_packet;
 
     bh = qemu_bh_new(lan9118_tick, s);
-    s->timer = ptimer_init(bh);
+    s->timer = ptimer_init(bh, PTIMER_POLICY_DEFAULT);
     ptimer_set_freq(s->timer, 10000);
     ptimer_set_limit(s->timer, 0xffff, 1);
 
diff --git a/hw/timer/allwinner-a10-pit.c b/hw/timer/allwinner-a10-pit.c
index 3385e5d..22ceabe 100644
--- a/hw/timer/allwinner-a10-pit.c
+++ b/hw/timer/allwinner-a10-pit.c
@@ -267,7 +267,7 @@  static void a10_pit_init(Object *obj)
         tc->container = s;
         tc->index = i;
         bh[i] = qemu_bh_new(a10_pit_timer_cb, tc);
-        s->timer[i] = ptimer_init(bh[i]);
+        s->timer[i] = ptimer_init(bh[i], PTIMER_POLICY_DEFAULT);
     }
 }
 
diff --git a/hw/timer/arm_timer.c b/hw/timer/arm_timer.c
index 111a16d..98fddd7 100644
--- a/hw/timer/arm_timer.c
+++ b/hw/timer/arm_timer.c
@@ -171,7 +171,7 @@  static arm_timer_state *arm_timer_init(uint32_t freq)
     s->control = TIMER_CTRL_IE;
 
     bh = qemu_bh_new(arm_timer_tick, s);
-    s->timer = ptimer_init(bh);
+    s->timer = ptimer_init(bh, PTIMER_POLICY_DEFAULT);
     vmstate_register(NULL, -1, &vmstate_arm_timer, s);
     return s;
 }
diff --git a/hw/timer/aspeed_timer.c b/hw/timer/aspeed_timer.c
index 4b94808..f48799d 100644
--- a/hw/timer/aspeed_timer.c
+++ b/hw/timer/aspeed_timer.c
@@ -356,7 +356,7 @@  static void aspeed_init_one_timer(AspeedTimerCtrlState *s, uint8_t id)
 
     t->id = id;
     bh = qemu_bh_new(aspeed_timer_expire, t);
-    t->timer = ptimer_init(bh);
+    t->timer = ptimer_init(bh, PTIMER_POLICY_DEFAULT);
 }
 
 static void aspeed_timer_realize(DeviceState *dev, Error **errp)
diff --git a/hw/timer/digic-timer.c b/hw/timer/digic-timer.c
index 0f21faf..e1fcf73 100644
--- a/hw/timer/digic-timer.c
+++ b/hw/timer/digic-timer.c
@@ -127,7 +127,7 @@  static void digic_timer_init(Object *obj)
 {
     DigicTimerState *s = DIGIC_TIMER(obj);
 
-    s->ptimer = ptimer_init(NULL);
+    s->ptimer = ptimer_init(NULL, PTIMER_POLICY_DEFAULT);
 
     /*
      * FIXME: there is no documentation on Digic timer
diff --git a/hw/timer/etraxfs_timer.c b/hw/timer/etraxfs_timer.c
index 36d8f46..8e18236 100644
--- a/hw/timer/etraxfs_timer.c
+++ b/hw/timer/etraxfs_timer.c
@@ -322,9 +322,9 @@  static int etraxfs_timer_init(SysBusDevice *dev)
     t->bh_t0 = qemu_bh_new(timer0_hit, t);
     t->bh_t1 = qemu_bh_new(timer1_hit, t);
     t->bh_wd = qemu_bh_new(watchdog_hit, t);
-    t->ptimer_t0 = ptimer_init(t->bh_t0);
-    t->ptimer_t1 = ptimer_init(t->bh_t1);
-    t->ptimer_wd = ptimer_init(t->bh_wd);
+    t->ptimer_t0 = ptimer_init(t->bh_t0, PTIMER_POLICY_DEFAULT);
+    t->ptimer_t1 = ptimer_init(t->bh_t1, PTIMER_POLICY_DEFAULT);
+    t->ptimer_wd = ptimer_init(t->bh_wd, PTIMER_POLICY_DEFAULT);
 
     sysbus_init_irq(dev, &t->irq);
     sysbus_init_irq(dev, &t->nmi);
diff --git a/hw/timer/exynos4210_mct.c b/hw/timer/exynos4210_mct.c
index ae69345..0c18934 100644
--- a/hw/timer/exynos4210_mct.c
+++ b/hw/timer/exynos4210_mct.c
@@ -1431,15 +1431,16 @@  static void exynos4210_mct_init(Object *obj)
 
     /* Global timer */
     bh[0] = qemu_bh_new(exynos4210_gfrc_event, s);
-    s->g_timer.ptimer_frc = ptimer_init(bh[0]);
+    s->g_timer.ptimer_frc = ptimer_init(bh[0], PTIMER_POLICY_DEFAULT);
     memset(&s->g_timer.reg, 0, sizeof(struct gregs));
 
     /* Local timers */
     for (i = 0; i < 2; i++) {
         bh[0] = qemu_bh_new(exynos4210_ltick_event, &s->l_timer[i]);
         bh[1] = qemu_bh_new(exynos4210_lfrc_event, &s->l_timer[i]);
-        s->l_timer[i].tick_timer.ptimer_tick = ptimer_init(bh[0]);
-        s->l_timer[i].ptimer_frc = ptimer_init(bh[1]);
+        s->l_timer[i].tick_timer.ptimer_tick =
+                                   ptimer_init(bh[0], PTIMER_POLICY_DEFAULT);
+        s->l_timer[i].ptimer_frc = ptimer_init(bh[1], PTIMER_POLICY_DEFAULT);
         s->l_timer[i].id = i;
     }
 
diff --git a/hw/timer/exynos4210_pwm.c b/hw/timer/exynos4210_pwm.c
index 0e9e2e9..f576507 100644
--- a/hw/timer/exynos4210_pwm.c
+++ b/hw/timer/exynos4210_pwm.c
@@ -390,7 +390,7 @@  static void exynos4210_pwm_init(Object *obj)
     for (i = 0; i < EXYNOS4210_PWM_TIMERS_NUM; i++) {
         bh = qemu_bh_new(exynos4210_pwm_tick, &s->timer[i]);
         sysbus_init_irq(dev, &s->timer[i].irq);
-        s->timer[i].ptimer = ptimer_init(bh);
+        s->timer[i].ptimer = ptimer_init(bh, PTIMER_POLICY_DEFAULT);
         s->timer[i].id = i;
         s->timer[i].parent = s;
     }
diff --git a/hw/timer/exynos4210_rtc.c b/hw/timer/exynos4210_rtc.c
index da4dd45..1a648c5 100644
--- a/hw/timer/exynos4210_rtc.c
+++ b/hw/timer/exynos4210_rtc.c
@@ -555,12 +555,12 @@  static void exynos4210_rtc_init(Object *obj)
     QEMUBH *bh;
 
     bh = qemu_bh_new(exynos4210_rtc_tick, s);
-    s->ptimer = ptimer_init(bh);
+    s->ptimer = ptimer_init(bh, PTIMER_POLICY_DEFAULT);
     ptimer_set_freq(s->ptimer, RTC_BASE_FREQ);
     exynos4210_rtc_update_freq(s, 0);
 
     bh = qemu_bh_new(exynos4210_rtc_1Hz_tick, s);
-    s->ptimer_1Hz = ptimer_init(bh);
+    s->ptimer_1Hz = ptimer_init(bh, PTIMER_POLICY_DEFAULT);
     ptimer_set_freq(s->ptimer_1Hz, RTC_BASE_FREQ);
 
     sysbus_init_irq(dev, &s->alm_irq);
diff --git a/hw/timer/grlib_gptimer.c b/hw/timer/grlib_gptimer.c
index dd000f5..712d1ae 100644
--- a/hw/timer/grlib_gptimer.c
+++ b/hw/timer/grlib_gptimer.c
@@ -363,7 +363,7 @@  static int grlib_gptimer_init(SysBusDevice *dev)
 
         timer->unit   = unit;
         timer->bh     = qemu_bh_new(grlib_gptimer_hit, timer);
-        timer->ptimer = ptimer_init(timer->bh);
+        timer->ptimer = ptimer_init(timer->bh, PTIMER_POLICY_DEFAULT);
         timer->id     = i;
 
         /* One IRQ line for each timer */
diff --git a/hw/timer/imx_epit.c b/hw/timer/imx_epit.c
index eddf348..f34d7f7 100644
--- a/hw/timer/imx_epit.c
+++ b/hw/timer/imx_epit.c
@@ -314,10 +314,10 @@  static void imx_epit_realize(DeviceState *dev, Error **errp)
                           0x00001000);
     sysbus_init_mmio(sbd, &s->iomem);
 
-    s->timer_reload = ptimer_init(NULL);
+    s->timer_reload = ptimer_init(NULL, PTIMER_POLICY_DEFAULT);
 
     bh = qemu_bh_new(imx_epit_cmp, s);
-    s->timer_cmp = ptimer_init(bh);
+    s->timer_cmp = ptimer_init(bh, PTIMER_POLICY_DEFAULT);
 }
 
 static void imx_epit_class_init(ObjectClass *klass, void *data)
diff --git a/hw/timer/imx_gpt.c b/hw/timer/imx_gpt.c
index 3c2f01a..b864ac3 100644
--- a/hw/timer/imx_gpt.c
+++ b/hw/timer/imx_gpt.c
@@ -440,7 +440,7 @@  static void imx_gpt_realize(DeviceState *dev, Error **errp)
     sysbus_init_mmio(sbd, &s->iomem);
 
     bh = qemu_bh_new(imx_gpt_timeout, s);
-    s->timer = ptimer_init(bh);
+    s->timer = ptimer_init(bh, PTIMER_POLICY_DEFAULT);
 }
 
 static void imx_gpt_class_init(ObjectClass *klass, void *data)
diff --git a/hw/timer/lm32_timer.c b/hw/timer/lm32_timer.c
index 3198355..a7a6b57 100644
--- a/hw/timer/lm32_timer.c
+++ b/hw/timer/lm32_timer.c
@@ -183,7 +183,7 @@  static int lm32_timer_init(SysBusDevice *dev)
     sysbus_init_irq(dev, &s->irq);
 
     s->bh = qemu_bh_new(timer_hit, s);
-    s->ptimer = ptimer_init(s->bh);
+    s->ptimer = ptimer_init(s->bh, PTIMER_POLICY_DEFAULT);
     ptimer_set_freq(s->ptimer, s->freq_hz);
 
     memory_region_init_io(&s->iomem, OBJECT(s), &timer_ops, s,
diff --git a/hw/timer/milkymist-sysctl.c b/hw/timer/milkymist-sysctl.c
index 5f29480..818f2d9 100644
--- a/hw/timer/milkymist-sysctl.c
+++ b/hw/timer/milkymist-sysctl.c
@@ -280,8 +280,8 @@  static int milkymist_sysctl_init(SysBusDevice *dev)
 
     s->bh0 = qemu_bh_new(timer0_hit, s);
     s->bh1 = qemu_bh_new(timer1_hit, s);
-    s->ptimer0 = ptimer_init(s->bh0);
-    s->ptimer1 = ptimer_init(s->bh1);
+    s->ptimer0 = ptimer_init(s->bh0, PTIMER_POLICY_DEFAULT);
+    s->ptimer1 = ptimer_init(s->bh1, PTIMER_POLICY_DEFAULT);
     ptimer_set_freq(s->ptimer0, s->freq_hz);
     ptimer_set_freq(s->ptimer1, s->freq_hz);
 
diff --git a/hw/timer/puv3_ost.c b/hw/timer/puv3_ost.c
index 93650b7..0b3d717 100644
--- a/hw/timer/puv3_ost.c
+++ b/hw/timer/puv3_ost.c
@@ -125,7 +125,7 @@  static int puv3_ost_init(SysBusDevice *dev)
     sysbus_init_irq(dev, &s->irq);
 
     s->bh = qemu_bh_new(puv3_ost_tick, s);
-    s->ptimer = ptimer_init(s->bh);
+    s->ptimer = ptimer_init(s->bh, PTIMER_POLICY_DEFAULT);
     ptimer_set_freq(s->ptimer, 50 * 1000 * 1000);
 
     memory_region_init_io(&s->iomem, OBJECT(s), &puv3_ost_ops, s, "puv3_ost",
diff --git a/hw/timer/sh_timer.c b/hw/timer/sh_timer.c
index 255b2fc..9afb2d0 100644
--- a/hw/timer/sh_timer.c
+++ b/hw/timer/sh_timer.c
@@ -203,7 +203,7 @@  static void *sh_timer_init(uint32_t freq, int feat, qemu_irq irq)
     s->irq = irq;
 
     bh = qemu_bh_new(sh_timer_tick, s);
-    s->timer = ptimer_init(bh);
+    s->timer = ptimer_init(bh, PTIMER_POLICY_DEFAULT);
 
     sh_timer_write(s, OFFSET_TCOR >> 2, s->tcor);
     sh_timer_write(s, OFFSET_TCNT >> 2, s->tcnt);
diff --git a/hw/timer/slavio_timer.c b/hw/timer/slavio_timer.c
index fb3e08b..bfee1f3 100644
--- a/hw/timer/slavio_timer.c
+++ b/hw/timer/slavio_timer.c
@@ -389,7 +389,7 @@  static int slavio_timer_init1(SysBusDevice *dev)
         tc->timer_index = i;
 
         bh = qemu_bh_new(slavio_timer_irq, tc);
-        s->cputimer[i].timer = ptimer_init(bh);
+        s->cputimer[i].timer = ptimer_init(bh, PTIMER_POLICY_DEFAULT);
         ptimer_set_period(s->cputimer[i].timer, TIMER_PERIOD);
 
         size = i == 0 ? SYS_TIMER_SIZE : CPU_TIMER_SIZE;
diff --git a/hw/timer/xilinx_timer.c b/hw/timer/xilinx_timer.c
index 2ea970d..59439c0 100644
--- a/hw/timer/xilinx_timer.c
+++ b/hw/timer/xilinx_timer.c
@@ -218,7 +218,7 @@  static void xilinx_timer_realize(DeviceState *dev, Error **errp)
         xt->parent = t;
         xt->nr = i;
         xt->bh = qemu_bh_new(timer_hit, xt);
-        xt->ptimer = ptimer_init(xt->bh);
+        xt->ptimer = ptimer_init(xt->bh, PTIMER_POLICY_DEFAULT);
         ptimer_set_freq(xt->ptimer, t->freq_hz);
     }
 
diff --git a/include/hw/ptimer.h b/include/hw/ptimer.h
index e397db5..69dbdc1 100644
--- a/include/hw/ptimer.h
+++ b/include/hw/ptimer.h
@@ -12,11 +12,16 @@ 
 #include "qemu/timer.h"
 #include "migration/vmstate.h"
 
+/* Stop the timer if period/counter is equal to 0.  */
+#define PTIMER_POLICY_DEFAULT               0
+/* Counter = 0 triggers IRQ after one period.  */
+#define PTIMER_POLICY_CNT_0_DEFERRED_TRIG   (1 << 0)
+
 /* ptimer.c */
 typedef struct ptimer_state ptimer_state;
 typedef void (*ptimer_cb)(void *opaque);
 
-ptimer_state *ptimer_init(QEMUBH *bh);
+ptimer_state *ptimer_init(QEMUBH *bh, uint8_t policy_mask);
 void ptimer_set_period(ptimer_state *s, int64_t period);
 void ptimer_set_freq(ptimer_state *s, uint32_t freq);
 uint64_t ptimer_get_limit(ptimer_state *s);