PTimer fixes and ARM MPTimer conversion

PATCH Superseded Dmitry Osipenko 1 participant 5 messages Jan 5, 2016

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Dmitry Osipenko

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2016-01-05 13:45 UTC #0 lore raw

v9 cover PTimer fixes and ARM MPTimer conversion

Changelog for ARM MPTimer QEMUTimer to ptimer conversion:

V2: Fixed changing periodic timer counter value "on the fly". I added a
test to the gist to cover that issue.

V3: Fixed starting the timer with load = 0 and counter != 0, added tests
to the gist for this issue. Changed vmstate version for all VMSD's, since loadvm doesn't check version of nested VMSD.

V4: Fixed spurious IT bit set for the timer starting in the periodic mode
with counter = 0. Test added.

V5: Code cleanup, now depends on ptimer_set_limit() fix.

V6: No code change, added test to check ptimer_get_count() with corrected
.limit value.

V7: No change.

V8: No change.

V9: No change.

ARM MPTimer tests: https://gist.github.com/digetx/dbd46109503b1a91941a

Patch for ptimer is introduced since V5 of "ARM MPTimer conversion".

Changelog for the "ptimer fixes" patch:

V5: Only fixed ptimer_set_limit() for the disabled timer.

V6: As was pointed by Peter Maydell, there are other issues beyond
ptimer_set_limit(), so V6 supposed to cover all those issues.

V7: Added accidentally removed !use_icount check.
Added missed "else" statement.

V8: Adjust period instead of the limit and do it for periodic timer only
(.limit adjusting bug). Added patch/fix for freq/period change and ptimer_get_count() improvement.

V9: Don't do wrap around if counter == 0, otherwise polled periodic
timer won't ever return counter = 0.

Dmitry Osipenko (4):
hw/ptimer: Fix issues caused by the adjusted timer limit value hw/ptimer: Perform tick and counter wrap around if timer already
expired
hw/ptimer: Update .delta on period/freq change
arm_mptimer: Convert to use ptimer

 hw/core/ptimer.c               |  94 ++++++++++++++++++++++++-----------
 hw/timer/arm_mptimer.c         | 110 ++++++++++++++++++-----------------------
 include/hw/timer/arm_mptimer.h |   4 +-
 3 files changed, 115 insertions(+), 93 deletions(-)

Signature · 1 line

2.6.4

Dmitry Osipenko

author

2016-01-05 13:45 UTC #1 lore raw

PATCH v9 1/4 hw/ptimer: Fix issues caused by the adjusted timer limit value

Multiple issues here related to the timer with a adjusted .limit value:

1) ptimer_get_count() returns incorrect counter value for the disabled timer after loading the counter with a small value, because adjusted limit value is used instead of the original.

For instance:
1) ptimer_stop(t)
2) ptimer_set_period(t, 1)
3) ptimer_set_limit(t, 0, 1)
4) ptimer_get_count(t) <-- would return 10000 instead of 0

2) ptimer_get_count() might return incorrect value for the timer running with a adjusted limit value.

For instance:
1) ptimer_stop(t)
2) ptimer_set_period(t, 1)
3) ptimer_set_limit(t, 10, 1)
4) ptimer_run(t)
5) ptimer_get_count(t) <-- might return value > 10

3) Neither ptimer_set_period() nor ptimer_set_freq() are adjusting the limit value, so it is still possible to make timer timeout value arbitrary small.

For instance:
1) ptimer_set_period(t, 10000)
2) ptimer_set_limit(t, 1, 0)
3) ptimer_set_period(t, 1) <-- bypass limit correction

Fix all of the above issues by adjusting timer period instead of the limit. Do the adjust for periodic timer only.

Signed-off-by Dmitry Osipenko <[email protected]>

---
 hw/core/ptimer.c | 59 ++++++++++++++++++++++++++++++++++----------------------
 1 file changed, 36 insertions(+), 23 deletions(-)

hw/core/ptimer.c +36 ~~-23~~

index edf077c..035af97 100644
@@ -34,20 +34,39 @@ static void ptimer_trigger(ptimer_state *s)
 
 static void ptimer_reload(ptimer_state *s)
 {
-    if (s->delta == 0) {
+    uint32_t period_frac = s->period_frac;
+    uint64_t period = s->period;
+    uint64_t delta = s->delta;
+    uint64_t limit = s->limit;
+
+    if (delta == 0) {
         ptimer_trigger(s);
-        s->delta = s->limit;
+        delta = limit;
     }
-    if (s->delta == 0 || s->period == 0) {
+    if (delta == 0 || period == 0) {
         fprintf(stderr, "Timer with period zero, disabling\n");
         s->enabled = 0;
         return;
     }
 
+    /*
+     * Artificially limit timeout rate to something
+     * achievable under QEMU.  Otherwise, QEMU spends all
+     * its time generating timer interrupts, and there
+     * is no forward progress.
+     * About ten microseconds is the fastest that really works
+     * on the current generation of host machines.
+     */
+
+    if ((s->enabled == 1) && (limit * period < 10000)) {
+        period = 10000 / limit;
+        period_frac = 0;
+    }
+
     s->last_event = s->next_event;
-    s->next_event = s->last_event + s->delta * s->period;
-    if (s->period_frac) {
-        s->next_event += ((int64_t)s->period_frac * s->delta) >> 32;
+    s->next_event = s->last_event + delta * period;
+    if (period_frac) {
+        s->next_event += ((int64_t)period_frac * delta) >> 32;
     }
     timer_mod(s->timer, s->next_event);
 }

@@ -82,6 +101,8 @@ uint64_t ptimer_get_count(ptimer_state *s)
             uint64_t div;
             int clz1, clz2;
             int shift;
+            uint32_t period_frac = s->period_frac;
+            uint64_t period = s->period;
 
             /* We need to divide time by period, where time is stored in
                rem (64-bit integer) and period is stored in period/period_frac

@@ -93,8 +114,13 @@ uint64_t ptimer_get_count(ptimer_state *s)
                backwards.
             */
 
+            if ((s->enabled == 1) && (s->limit * period < 10000)) {
+                period = 10000 / s->limit;
+                period_frac = 0;
+            }
+
             rem = s->next_event - now;
-            div = s->period;
+            div = period;
 
             clz1 = clz64(rem);
             clz2 = clz64(div);

@@ -103,13 +129,13 @@ uint64_t ptimer_get_count(ptimer_state *s)
             rem <<= shift;
             div <<= shift;
             if (shift >= 32) {
-                div |= ((uint64_t)s->period_frac << (shift - 32));
+                div |= ((uint64_t)period_frac << (shift - 32));
             } else {
                 if (shift != 0)
-                    div |= (s->period_frac >> (32 - shift));
+                    div |= (period_frac >> (32 - shift));
                 /* Look at remaining bits of period_frac and round div up if 
                    necessary.  */
-                if ((uint32_t)(s->period_frac << shift))
+                if ((uint32_t)(period_frac << shift))
                     div += 1;
             }
             counter = rem / div;

@@ -181,19 +207,6 @@ void ptimer_set_freq(ptimer_state *s, uint32_t freq)
    count = limit.  */
 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload)
 {
-    /*
-     * Artificially limit timeout rate to something
-     * achievable under QEMU.  Otherwise, QEMU spends all
-     * its time generating timer interrupts, and there
-     * is no forward progress.
-     * About ten microseconds is the fastest that really works
-     * on the current generation of host machines.
-     */
-
-    if (!use_icount && limit * s->period < 10000 && s->period) {
-        limit = 10000 / s->period;
-    }
-
     s->limit = limit;
     if (reload)
         s->delta = limit;

Signature · 1 line

2.6.4

Dmitry Osipenko

author

2016-01-05 13:45 UTC #2 lore raw

PATCH v9 2/4 hw/ptimer: Perform tick and counter wrap around if timer already expired

In reply to Dmitry Osipenko

ptimer_get_count() might be called while QEMU timer already been expired. In that case ptimer would return counter = 0, which might be undesirable in case of polled timer. Do counter wrap around for periodic timer to keep it distributed.

In addition, there is no reason to keep expired timer tick deferred, so just perform the tick from ptimer_get_count().

Signed-off-by Dmitry Osipenko <[email protected]>

---
 hw/core/ptimer.c | 35 +++++++++++++++++++++++++++++------
 1 file changed, 29 insertions(+), 6 deletions(-)

hw/core/ptimer.c +29 -6

index 035af97..ff0586b 100644
@@ -85,15 +85,21 @@ static void ptimer_tick(void *opaque)
 
 uint64_t ptimer_get_count(ptimer_state *s)
 {
+    int enabled = s->enabled;
     int64_t now;
+    int64_t next;
     uint64_t counter;
+    int expired;
+    int oneshot;
 
-    if (s->enabled) {
+    if (enabled) {
         now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+        next = s->next_event;
+        expired = (now - next >= 0);
+        oneshot = (enabled == 2);
         /* Figure out the current counter value.  */
-        if (now - s->next_event > 0
-            || s->period == 0) {
-            /* Prevent timer underflowing if it should already have
+        if ((s->period == 0) || (expired && oneshot)) {
+            /* Prevent one-shot timer underflowing if it should already have
                triggered.  */
             counter = 0;
         } else {

@@ -114,12 +120,12 @@ uint64_t ptimer_get_count(ptimer_state *s)
                backwards.
             */
 
-            if ((s->enabled == 1) && (s->limit * period < 10000)) {
+            if (!oneshot && (s->limit * period < 10000)) {
                 period = 10000 / s->limit;
                 period_frac = 0;
             }
 
-            rem = s->next_event - now;
+            rem = expired ? now - next : next - now;
             div = period;
 
             clz1 = clz64(rem);

@@ -139,6 +145,23 @@ uint64_t ptimer_get_count(ptimer_state *s)
                     div += 1;
             }
             counter = rem / div;
+
+            if (expired && (counter != 0)) {
+                /* Wrap around periodic counter.  */
+                counter = s->delta = s->limit - counter % s->limit;
+            }
+        }
+
+        if (expired) {
+            if (counter == 0) {
+                ptimer_tick(s);
+            } else {
+                /* Don't use ptimer_tick() for the periodic timer since it
+                 * would reset the delta value.
+                 */
+                ptimer_trigger(s);
+                ptimer_reload(s);
+            }
         }
     } else {
         counter = s->delta;

Signature · 1 line

2.6.4

Dmitry Osipenko

author

2016-01-05 13:45 UTC #3 lore raw

PATCH v9 3/4 hw/ptimer: Update .delta on period/freq change

In reply to Dmitry Osipenko

Delta value must be updated on period/freq change, otherwise running timer would be restarted (counter reloaded with old delta). Only m68k/mcf520x and arm/arm_timer devices are currently doing freq change correctly, i.e. stopping the timer. Perform delta update to fix affected devices and eliminate potential further mistakes.

Signed-off-by Dmitry Osipenko <[email protected]>

---
 hw/core/ptimer.c | 2 ++
 1 file changed, 2 insertions(+)

hw/core/ptimer.c +2 -0

index ff0586b..eb4eb4b 100644
@@ -207,6 +207,7 @@ void ptimer_stop(ptimer_state *s)
 /* Set counter increment interval in nanoseconds.  */
 void ptimer_set_period(ptimer_state *s, int64_t period)
 {
+    s->delta = ptimer_get_count(s);
     s->period = period;
     s->period_frac = 0;
     if (s->enabled) {

@@ -218,6 +219,7 @@ 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)
 {
+    s->delta = ptimer_get_count(s);
     s->period = 1000000000ll / freq;
     s->period_frac = (1000000000ll << 32) / freq;
     if (s->enabled) {

Signature · 1 line

2.6.4

Dmitry Osipenko

author

2016-01-05 13:45 UTC #4 lore raw

PATCH v9 4/4 arm_mptimer: Convert to use ptimer

In reply to Dmitry Osipenko

Current ARM MPTimer implementation uses QEMUTimer for the actual timer, this implementation isn't complete and mostly tries to duplicate of what generic ptimer is already doing fine.

Conversion to ptimer brings the following benefits and fixes:
- Simple timer pausing implementation
- Fixes counter value preservation after stopping the timer
- Code simplification and reduction

Bump VMSD to version 3, since VMState is changed and is not compatible with the previous implementation.

Signed-off-by Dmitry Osipenko <[email protected]>

---
 hw/timer/arm_mptimer.c         | 110 ++++++++++++++++++-----------------------
 include/hw/timer/arm_mptimer.h |   4 +-
 2 files changed, 49 insertions(+), 65 deletions(-)

hw/timer/arm_mptimer.c +48 ~~-62~~

index 3e59c2a..c06da5e 100644
@@ -19,8 +19,9 @@
  * with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
+#include "hw/ptimer.h"
 #include "hw/timer/arm_mptimer.h"
-#include "qemu/timer.h"
+#include "qemu/main-loop.h"
 #include "qom/cpu.h"
 
 /* This device implements the per-cpu private timer and watchdog block

@@ -47,28 +48,10 @@ static inline uint32_t timerblock_scale(TimerBlock *tb)
     return (((tb->control >> 8) & 0xff) + 1) * 10;
 }
 
-static void timerblock_reload(TimerBlock *tb, int restart)
-{
-    if (tb->count == 0) {
-        return;
-    }
-    if (restart) {
-        tb->tick = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
-    }
-    tb->tick += (int64_t)tb->count * timerblock_scale(tb);
-    timer_mod(tb->timer, tb->tick);
-}
-
 static void timerblock_tick(void *opaque)
 {
     TimerBlock *tb = (TimerBlock *)opaque;
     tb->status = 1;
-    if (tb->control & 2) {
-        tb->count = tb->load;
-        timerblock_reload(tb, 0);
-    } else {
-        tb->count = 0;
-    }
     timerblock_update_irq(tb);
 }

@@ -76,21 +59,11 @@ static uint64_t timerblock_read(void *opaque, hwaddr addr,
                                 unsigned size)
 {
     TimerBlock *tb = (TimerBlock *)opaque;
-    int64_t val;
     switch (addr) {
     case 0: /* Load */
         return tb->load;
     case 4: /* Counter.  */
-        if (((tb->control & 1) == 0) || (tb->count == 0)) {
-            return 0;
-        }
-        /* Slow and ugly, but hopefully won't happen too often.  */
-        val = tb->tick - qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
-        val /= timerblock_scale(tb);
-        if (val < 0) {
-            val = 0;
-        }
-        return val;
+        return ptimer_get_count(tb->timer);
     case 8: /* Control.  */
         return tb->control;
     case 12: /* Interrupt status.  */

@@ -100,6 +73,19 @@ static uint64_t timerblock_read(void *opaque, hwaddr addr,
     }
 }
 
+static void timerblock_run(TimerBlock *tb, uint64_t count, int set_count)
+{
+    if (set_count) {
+        if (((tb->control & 3) == 3) && (count == 0)) {
+            count = tb->load;
+        }
+        ptimer_set_count(tb->timer, count);
+    }
+    if ((tb->control & 1) && (count != 0)) {
+        ptimer_run(tb->timer, !(tb->control & 2));
+    }
+}
+
 static void timerblock_write(void *opaque, hwaddr addr,
                              uint64_t value, unsigned size)
 {

@@ -108,32 +94,34 @@ static void timerblock_write(void *opaque, hwaddr addr,
     switch (addr) {
     case 0: /* Load */
         tb->load = value;
-        /* Fall through.  */
-    case 4: /* Counter.  */
-        if ((tb->control & 1) && tb->count) {
-            /* Cancel the previous timer.  */
-            timer_del(tb->timer);
+        /* Setting load to 0 stops the timer.  */
+        if (tb->load == 0) {
+            ptimer_stop(tb->timer);
         }
-        tb->count = value;
-        if (tb->control & 1) {
-            timerblock_reload(tb, 1);
+        ptimer_set_limit(tb->timer, tb->load, 1);
+        timerblock_run(tb, tb->load, 0);
+        break;
+    case 4: /* Counter.  */
+        /* Setting counter to 0 stops the one-shot timer.  */
+        if (!(tb->control & 2) && (value == 0)) {
+            ptimer_stop(tb->timer);
         }
+        timerblock_run(tb, value, 1);
         break;
     case 8: /* Control.  */
         old = tb->control;
         tb->control = value;
-        if (value & 1) {
-            if ((old & 1) && (tb->count != 0)) {
-                /* Do nothing if timer is ticking right now.  */
-                break;
-            }
-            if (tb->control & 2) {
-                tb->count = tb->load;
-            }
-            timerblock_reload(tb, 1);
-        } else if (old & 1) {
-            /* Shutdown the timer.  */
-            timer_del(tb->timer);
+        /* Timer mode switch requires ptimer to be stopped.  */
+        if ((old & 3) != (tb->control & 3)) {
+            ptimer_stop(tb->timer);
+        }
+        if (!(tb->control & 1)) {
+            break;
+        }
+        ptimer_set_period(tb->timer, timerblock_scale(tb));
+        if ((old & 3) != (tb->control & 3)) {
+            value = ptimer_get_count(tb->timer);
+            timerblock_run(tb, value, 1);
         }
         break;
     case 12: /* Interrupt status.  */

@@ -184,13 +172,12 @@ static const MemoryRegionOps timerblock_ops = {
 
 static void timerblock_reset(TimerBlock *tb)
 {
-    tb->count = 0;
     tb->load = 0;
     tb->control = 0;
     tb->status = 0;
-    tb->tick = 0;
     if (tb->timer) {
-        timer_del(tb->timer);
+        ptimer_stop(tb->timer);
+        ptimer_set_limit(tb->timer, 0, 1);
     }
 }

@@ -235,7 +222,8 @@ static void arm_mptimer_realize(DeviceState *dev, Error **errp)
      */
     for (i = 0; i < s->num_cpu; i++) {
         TimerBlock *tb = &s->timerblock[i];
-        tb->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, timerblock_tick, tb);
+        QEMUBH *bh = qemu_bh_new(timerblock_tick, tb);
+        tb->timer = ptimer_init(bh);
         sysbus_init_irq(sbd, &tb->irq);
         memory_region_init_io(&tb->iomem, OBJECT(s), &timerblock_ops, tb,
                               "arm_mptimer_timerblock", 0x20);

@@ -245,26 +233,24 @@ static void arm_mptimer_realize(DeviceState *dev, Error **errp)
 
 static const VMStateDescription vmstate_timerblock = {
     .name = "arm_mptimer_timerblock",
-    .version_id = 2,
-    .minimum_version_id = 2,
+    .version_id = 3,
+    .minimum_version_id = 3,
     .fields = (VMStateField[]) {
-        VMSTATE_UINT32(count, TimerBlock),
         VMSTATE_UINT32(load, TimerBlock),
         VMSTATE_UINT32(control, TimerBlock),
         VMSTATE_UINT32(status, TimerBlock),
-        VMSTATE_INT64(tick, TimerBlock),
-        VMSTATE_TIMER_PTR(timer, TimerBlock),
+        VMSTATE_PTIMER(timer, TimerBlock),
         VMSTATE_END_OF_LIST()
     }
 };
 
 static const VMStateDescription vmstate_arm_mptimer = {
     .name = "arm_mptimer",
-    .version_id = 2,
-    .minimum_version_id = 2,
+    .version_id = 3,
+    .minimum_version_id = 3,
     .fields = (VMStateField[]) {
         VMSTATE_STRUCT_VARRAY_UINT32(timerblock, ARMMPTimerState, num_cpu,
-                                     2, vmstate_timerblock, TimerBlock),
+                                     3, vmstate_timerblock, TimerBlock),
         VMSTATE_END_OF_LIST()
     }
 };

include/hw/timer/arm_mptimer.h +1 -3

index b34cba0..93db61b 100644
@@ -27,12 +27,10 @@
 
 /* State of a single timer or watchdog block */
 typedef struct {
-    uint32_t count;
     uint32_t load;
     uint32_t control;
     uint32_t status;
-    int64_t tick;
-    QEMUTimer *timer;
+    struct ptimer_state *timer;
     qemu_irq irq;
     MemoryRegion iomem;
 } TimerBlock;

Signature · 1 line

2.6.4