diff --git a/include/hw/ptimer.h b/include/hw/ptimer.h
index 4c321f65dcb..412763fffb2 100644
--- a/include/hw/ptimer.h
+++ b/include/hw/ptimer.h
@@ -10,15 +10,24 @@
 
 #include "qemu/timer.h"
 
-/* The ptimer API implements a simple periodic countdown timer.
+/*
+ * The ptimer API implements a simple periodic countdown timer.
  * The countdown timer has a value (which can be read and written via
  * ptimer_get_count() and ptimer_set_count()). When it is enabled
  * using ptimer_run(), the value will count downwards at the frequency
  * which has been configured using ptimer_set_period() or ptimer_set_freq().
- * When it reaches zero it will trigger a QEMU bottom half handler, and
+ * When it reaches zero it will trigger a callback function, and
  * can be set to either reload itself from a specified limit value
  * and keep counting down, or to stop (as a one-shot timer).
  *
+ * A transaction-based API is used for modifying ptimer state: all calls
+ * to functions which modify ptimer state must be between matched calls to
+ * ptimer_transaction_begin() and ptimer_transaction_commit().
+ * When ptimer_transaction_commit() is called it will evaluate the state
+ * of the timer after all the changes in the transaction, and call the
+ * callback if necessary. (See the ptimer_init() documentation for the full
+ * list of state-modifying functions and detailed semantics of the callback.)
+ *
  * Forgetting to set the period/frequency (or setting it to zero) is a
  * bug in the QEMU device and will cause warning messages to be printed
  * to stderr when the guest attempts to enable the timer.
@@ -72,7 +81,7 @@
  * ptimer_set_count() or ptimer_set_limit() will not trigger the timer
  * (though it will cause a reload). Only a counter decrement to "0"
  * will cause a trigger. Not compatible with NO_IMMEDIATE_TRIGGER;
- * ptimer_init_with_bh() will assert() that you don't set both.
+ * ptimer_init() will assert() that you don't set both.
  */
 #define PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT (1 << 5)
 
@@ -80,17 +89,6 @@
 typedef struct ptimer_state ptimer_state;
 typedef void (*ptimer_cb)(void *opaque);
 
-/**
- * ptimer_init_with_bh - Allocate and return a new ptimer
- * @bh: QEMU bottom half which is run on timer expiry
- * @policy: PTIMER_POLICY_* bits specifying behaviour
- *
- * The ptimer returned must be freed using ptimer_free().
- * The ptimer takes ownership of @bh and will delete it
- * when the ptimer is eventually freed.
- */
-ptimer_state *ptimer_init_with_bh(QEMUBH *bh, uint8_t policy_mask);
-
 /**
  * ptimer_init - Allocate and return a new ptimer
  * @callback: function to call on ptimer expiry
@@ -127,8 +125,7 @@ ptimer_state *ptimer_init(ptimer_cb callback,
  * ptimer_free - Free a ptimer
  * @s: timer to free
  *
- * Free a ptimer created using ptimer_init_with_bh() (including
- * deleting the bottom half which it is using).
+ * Free a ptimer created using ptimer_init().
  */
 void ptimer_free(ptimer_state *s);
 
@@ -164,7 +161,7 @@ void ptimer_transaction_commit(ptimer_state *s);
  * may be more appropriate.
  *
  * This function will assert if it is called outside a
- * ptimer_transaction_begin/commit block, unless this is a bottom-half ptimer.
+ * ptimer_transaction_begin/commit block.
  */
 void ptimer_set_period(ptimer_state *s, int64_t period);
 
@@ -180,7 +177,7 @@ void ptimer_set_period(ptimer_state *s, int64_t period);
  * precise to fractions of a nanosecond, avoiding rounding errors.
  *
  * This function will assert if it is called outside a
- * ptimer_transaction_begin/commit block, unless this is a bottom-half ptimer.
+ * ptimer_transaction_begin/commit block.
  */
 void ptimer_set_freq(ptimer_state *s, uint32_t freq);
 
@@ -210,7 +207,7 @@ uint64_t ptimer_get_limit(ptimer_state *s);
  * reload the counter when their reload register is written to.
  *
  * This function will assert if it is called outside a
- * ptimer_transaction_begin/commit block, unless this is a bottom-half ptimer.
+ * ptimer_transaction_begin/commit block.
  */
 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload);
 
@@ -234,7 +231,7 @@ uint64_t ptimer_get_count(ptimer_state *s);
  * point in the future.
  *
  * This function will assert if it is called outside a
- * ptimer_transaction_begin/commit block, unless this is a bottom-half ptimer.
+ * ptimer_transaction_begin/commit block.
  */
 void ptimer_set_count(ptimer_state *s, uint64_t count);
 
@@ -243,15 +240,15 @@ void ptimer_set_count(ptimer_state *s, uint64_t count);
  * @s: ptimer
  * @oneshot: non-zero if this timer should only count down once
  *
- * Start a ptimer counting down; when it reaches zero the bottom half
- * passed to ptimer_init_with_bh() will be invoked.
+ * Start a ptimer counting down; when it reaches zero the callback function
+ * passed to ptimer_init() will be invoked.
  * If the @oneshot argument is zero,
  * the counter value will then be reloaded from the limit and it will
  * start counting down again. If @oneshot is non-zero, then the counter
  * will disable itself when it reaches zero.
  *
  * This function will assert if it is called outside a
- * ptimer_transaction_begin/commit block, unless this is a bottom-half ptimer.
+ * ptimer_transaction_begin/commit block.
  */
 void ptimer_run(ptimer_state *s, int oneshot);
 
@@ -266,7 +263,7 @@ void ptimer_run(ptimer_state *s, int oneshot);
  * restarted.
  *
  * This function will assert if it is called outside a
- * ptimer_transaction_begin/commit block, unless this is a bottom-half ptimer.
+ * ptimer_transaction_begin/commit block.
  */
 void ptimer_stop(ptimer_state *s);
 
diff --git a/hw/core/ptimer.c b/hw/core/ptimer.c
index 7239b8227cc..b5a54e25369 100644
--- a/hw/core/ptimer.c
+++ b/hw/core/ptimer.c
@@ -29,7 +29,6 @@ struct ptimer_state
     int64_t last_event;
     int64_t next_event;
     uint8_t policy_mask;
-    QEMUBH *bh;
     QEMUTimer *timer;
     ptimer_cb callback;
     void *callback_opaque;
@@ -46,12 +45,7 @@ struct ptimer_state
 /* Use a bottom-half routine to avoid reentrancy issues.  */
 static void ptimer_trigger(ptimer_state *s)
 {
-    if (s->bh) {
-        replay_bh_schedule_event(s->bh);
-    }
-    if (s->callback) {
-        s->callback(s->callback_opaque);
-    }
+    s->callback(s->callback_opaque);
 }
 
 static void ptimer_reload(ptimer_state *s, int delta_adjust)
@@ -296,15 +290,10 @@ uint64_t ptimer_get_count(ptimer_state *s)
 
 void ptimer_set_count(ptimer_state *s, uint64_t count)
 {
-    assert(s->in_transaction || !s->callback);
+    assert(s->in_transaction);
     s->delta = count;
     if (s->enabled) {
-        if (!s->callback) {
-            s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
-            ptimer_reload(s, 0);
-        } else {
-            s->need_reload = true;
-        }
+        s->need_reload = true;
     }
 }
 
@@ -312,7 +301,7 @@ void ptimer_run(ptimer_state *s, int oneshot)
 {
     bool was_disabled = !s->enabled;
 
-    assert(s->in_transaction || !s->callback);
+    assert(s->in_transaction);
 
     if (was_disabled && s->period == 0) {
         if (!qtest_enabled()) {
@@ -322,12 +311,7 @@ void ptimer_run(ptimer_state *s, int oneshot)
     }
     s->enabled = oneshot ? 2 : 1;
     if (was_disabled) {
-        if (!s->callback) {
-            s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
-            ptimer_reload(s, 0);
-        } else {
-            s->need_reload = true;
-        }
+        s->need_reload = true;
     }
 }
 
@@ -335,7 +319,7 @@ void ptimer_run(ptimer_state *s, int oneshot)
    is immediately restarted.  */
 void ptimer_stop(ptimer_state *s)
 {
-    assert(s->in_transaction || !s->callback);
+    assert(s->in_transaction);
 
     if (!s->enabled)
         return;
@@ -343,42 +327,30 @@ void ptimer_stop(ptimer_state *s)
     s->delta = ptimer_get_count(s);
     timer_del(s->timer);
     s->enabled = 0;
-    if (s->callback) {
-        s->need_reload = false;
-    }
+    s->need_reload = false;
 }
 
 /* Set counter increment interval in nanoseconds.  */
 void ptimer_set_period(ptimer_state *s, int64_t period)
 {
-    assert(s->in_transaction || !s->callback);
+    assert(s->in_transaction);
     s->delta = ptimer_get_count(s);
     s->period = period;
     s->period_frac = 0;
     if (s->enabled) {
-        if (!s->callback) {
-            s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
-            ptimer_reload(s, 0);
-        } else {
-            s->need_reload = true;
-        }
+        s->need_reload = true;
     }
 }
 
 /* Set counter frequency in Hz.  */
 void ptimer_set_freq(ptimer_state *s, uint32_t freq)
 {
-    assert(s->in_transaction || !s->callback);
+    assert(s->in_transaction);
     s->delta = ptimer_get_count(s);
     s->period = 1000000000ll / freq;
     s->period_frac = (1000000000ll << 32) / freq;
     if (s->enabled) {
-        if (!s->callback) {
-            s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
-            ptimer_reload(s, 0);
-        } else {
-            s->need_reload = true;
-        }
+        s->need_reload = true;
     }
 }
 
@@ -386,17 +358,12 @@ void ptimer_set_freq(ptimer_state *s, uint32_t freq)
    count = limit.  */
 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload)
 {
-    assert(s->in_transaction || !s->callback);
+    assert(s->in_transaction);
     s->limit = limit;
     if (reload)
         s->delta = limit;
     if (s->enabled && reload) {
-        if (!s->callback) {
-            s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
-            ptimer_reload(s, 0);
-        } else {
-            s->need_reload = true;
-        }
+        s->need_reload = true;
     }
 }
 
@@ -407,7 +374,7 @@ uint64_t ptimer_get_limit(ptimer_state *s)
 
 void ptimer_transaction_begin(ptimer_state *s)
 {
-    assert(!s->in_transaction || !s->callback);
+    assert(!s->in_transaction);
     s->in_transaction = true;
     s->need_reload = false;
 }
@@ -448,37 +415,12 @@ const VMStateDescription vmstate_ptimer = {
     }
 };
 
-ptimer_state *ptimer_init_with_bh(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;
-
-    /*
-     * These two policies are incompatible -- trigger-on-decrement implies
-     * a timer trigger when the count becomes 0, but no-immediate-trigger
-     * implies a trigger when the count stops being 0.
-     */
-    assert(!((policy_mask & PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT) &&
-             (policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)));
-    return s;
-}
-
 ptimer_state *ptimer_init(ptimer_cb callback, void *callback_opaque,
                           uint8_t policy_mask)
 {
     ptimer_state *s;
 
-    /*
-     * The callback function is mandatory; so we use it to distinguish
-     * old-style QEMUBH ptimers from new transaction API ptimers.
-     * (ptimer_init_with_bh() allows a NULL bh pointer and at least
-     * one device (digic-timer) passes NULL, so it's not the case
-     * that either s->bh != NULL or s->callback != NULL.)
-     */
+    /* The callback function is mandatory. */
     assert(callback);
 
     s = g_new0(ptimer_state, 1);
@@ -499,9 +441,6 @@ ptimer_state *ptimer_init(ptimer_cb callback, void *callback_opaque,
 
 void ptimer_free(ptimer_state *s)
 {
-    if (s->bh) {
-        qemu_bh_delete(s->bh);
-    }
     timer_free(s->timer);
     g_free(s);
 }
