ptimer: Rename PTIMER_POLICY_DEFAULT to PTIMER_POLICY_LEGACY

The traditional ptimer behaviour includes a collection of weird edge
case behaviours.  In 2016 we improved the ptimer implementation to
fix these and generally make the behaviour more flexible, with
ptimers opting in to the new behaviour by passing an appropriate set
of policy flags to ptimer_init().  For backwards-compatibility, we
defined PTIMER_POLICY_DEFAULT (which sets no flags) to give the old
weird behaviour.

This turns out to be a poor choice of name, because people writing
new devices which use ptimers are misled into thinking that the
default is probably a sensible choice of flags, when in fact it is
almost always not what you want.  Rename PTIMER_POLICY_DEFAULT to
PTIMER_POLICY_LEGACY and beef up the comment to more clearly say that
new devices should not be using it.

The code-change part of this commit was produced by
  sed -i -e 's/PTIMER_POLICY_DEFAULT/PTIMER_POLICY_LEGACY/g' $(git grep -l PTIMER_POLICY_DEFAULT)
with the exception of a test name string change in
tests/unit/ptimer-test.c which was added manually.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Francisco Iglesias <francisco.iglesias@amd.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220516103058.162280-1-peter.maydell@linaro.org

hw/arm/musicpal.c

@@ -464,7 +464,7 @@ static void mv88w8618_timer_init(SysBusDevice *dev, mv88w8618_timer_state *s,
     sysbus_init_irq(dev, &s->irq);
     s->freq = freq;
 
-    s->ptimer = ptimer_init(mv88w8618_timer_tick, s, PTIMER_POLICY_DEFAULT);
+    s->ptimer = ptimer_init(mv88w8618_timer_tick, s, PTIMER_POLICY_LEGACY);
 }
 
 static uint64_t mv88w8618_pit_read(void *opaque, hwaddr offset,

hw/dma/xilinx_axidma.c

@@ -552,7 +552,7 @@ static void xilinx_axidma_realize(DeviceState *dev, Error **errp)
 
         st->dma = s;
         st->nr = i;
-        st->ptimer = ptimer_init(timer_hit, st, PTIMER_POLICY_DEFAULT);
+        st->ptimer = ptimer_init(timer_hit, st, PTIMER_POLICY_LEGACY);
         ptimer_transaction_begin(st->ptimer);
         ptimer_set_freq(st->ptimer, s->freqhz);
         ptimer_transaction_commit(st->ptimer);

hw/dma/xlnx_csu_dma.c

@@ -666,7 +666,7 @@ static void xlnx_csu_dma_realize(DeviceState *dev, Error **errp)
     sysbus_init_irq(SYS_BUS_DEVICE(dev), &s->irq);
 
     s->src_timer = ptimer_init(xlnx_csu_dma_src_timeout_hit,
-                               s, PTIMER_POLICY_DEFAULT);
+                               s, PTIMER_POLICY_LEGACY);
 
     s->attr = MEMTXATTRS_UNSPECIFIED;
 

hw/m68k/mcf5206.c

@@ -152,7 +152,7 @@ static m5206_timer_state *m5206_timer_init(qemu_irq irq)
     m5206_timer_state *s;
 
     s = g_new0(m5206_timer_state, 1);
-    s->timer = ptimer_init(m5206_timer_trigger, s, PTIMER_POLICY_DEFAULT);
+    s->timer = ptimer_init(m5206_timer_trigger, s, PTIMER_POLICY_LEGACY);
     s->irq = irq;
     m5206_timer_reset(s);
     return s;

hw/m68k/mcf5208.c

@@ -197,7 +197,7 @@ static void mcf5208_sys_init(MemoryRegion *address_space, qemu_irq *pic)
     /* Timers.  */
     for (i = 0; i < 2; i++) {
         s = g_new0(m5208_timer_state, 1);
-        s->timer = ptimer_init(m5208_timer_trigger, s, PTIMER_POLICY_DEFAULT);
+        s->timer = ptimer_init(m5208_timer_trigger, s, PTIMER_POLICY_LEGACY);
         memory_region_init_io(&s->iomem, NULL, &m5208_timer_ops, s,
                               "m5208-timer", 0x00004000);
         memory_region_add_subregion(address_space, 0xfc080000 + 0x4000 * i,

hw/net/can/xlnx-zynqmp-can.c

@@ -1079,7 +1079,7 @@ static void xlnx_zynqmp_can_realize(DeviceState *dev, Error **errp)
 
     /* Allocate a new timer. */
     s->can_timer = ptimer_init(xlnx_zynqmp_can_ptimer_cb, s,
-                               PTIMER_POLICY_DEFAULT);
+                               PTIMER_POLICY_LEGACY);
 
     ptimer_transaction_begin(s->can_timer);
 

hw/net/fsl_etsec/etsec.c

@@ -393,7 +393,7 @@ static void etsec_realize(DeviceState *dev, Error **errp)
                               object_get_typename(OBJECT(dev)), dev->id, etsec);
     qemu_format_nic_info_str(qemu_get_queue(etsec->nic), etsec->conf.macaddr.a);
 
-    etsec->ptimer = ptimer_init(etsec_timer_hit, etsec, PTIMER_POLICY_DEFAULT);
+    etsec->ptimer = ptimer_init(etsec_timer_hit, etsec, PTIMER_POLICY_LEGACY);
     ptimer_transaction_begin(etsec->ptimer);
     ptimer_set_freq(etsec->ptimer, 100);
     ptimer_transaction_commit(etsec->ptimer);

hw/net/lan9118.c

@@ -1363,7 +1363,7 @@ static void lan9118_realize(DeviceState *dev, Error **errp)
     s->pmt_ctrl = 1;
     s->txp = &s->tx_packet;
 
-    s->timer = ptimer_init(lan9118_tick, s, PTIMER_POLICY_DEFAULT);
+    s->timer = ptimer_init(lan9118_tick, s, PTIMER_POLICY_LEGACY);
     ptimer_transaction_begin(s->timer);
     ptimer_set_freq(s->timer, 10000);
     ptimer_set_limit(s->timer, 0xffff, 1);

hw/rtc/exynos4210_rtc.c

@@ -564,14 +564,14 @@ static void exynos4210_rtc_init(Object *obj)
     Exynos4210RTCState *s = EXYNOS4210_RTC(obj);
     SysBusDevice *dev = SYS_BUS_DEVICE(obj);
 
-    s->ptimer = ptimer_init(exynos4210_rtc_tick, s, PTIMER_POLICY_DEFAULT);
+    s->ptimer = ptimer_init(exynos4210_rtc_tick, s, PTIMER_POLICY_LEGACY);
     ptimer_transaction_begin(s->ptimer);
     ptimer_set_freq(s->ptimer, RTC_BASE_FREQ);
     exynos4210_rtc_update_freq(s, 0);
     ptimer_transaction_commit(s->ptimer);
 
     s->ptimer_1Hz = ptimer_init(exynos4210_rtc_1Hz_tick,
-                                s, PTIMER_POLICY_DEFAULT);
+                                s, PTIMER_POLICY_LEGACY);
     ptimer_transaction_begin(s->ptimer_1Hz);
     ptimer_set_freq(s->ptimer_1Hz, RTC_BASE_FREQ);
     ptimer_transaction_commit(s->ptimer_1Hz);

hw/timer/allwinner-a10-pit.c

@@ -275,7 +275,7 @@ static void a10_pit_init(Object *obj)
 
         tc->container = s;
         tc->index = i;
-        s->timer[i] = ptimer_init(a10_pit_timer_cb, tc, PTIMER_POLICY_DEFAULT);
+        s->timer[i] = ptimer_init(a10_pit_timer_cb, tc, PTIMER_POLICY_LEGACY);
     }
 }
 

hw/timer/altera_timer.c

@@ -185,7 +185,7 @@ static void altera_timer_realize(DeviceState *dev, Error **errp)
         return;
     }
 
-    t->ptimer = ptimer_init(timer_hit, t, PTIMER_POLICY_DEFAULT);
+    t->ptimer = ptimer_init(timer_hit, t, PTIMER_POLICY_LEGACY);
     ptimer_transaction_begin(t->ptimer);
     ptimer_set_freq(t->ptimer, t->freq_hz);
     ptimer_transaction_commit(t->ptimer);

hw/timer/arm_timer.c

@@ -180,7 +180,7 @@ static arm_timer_state *arm_timer_init(uint32_t freq)
     s->freq = freq;
     s->control = TIMER_CTRL_IE;
 
-    s->timer = ptimer_init(arm_timer_tick, s, PTIMER_POLICY_DEFAULT);
+    s->timer = ptimer_init(arm_timer_tick, s, PTIMER_POLICY_LEGACY);
     vmstate_register(NULL, VMSTATE_INSTANCE_ID_ANY, &vmstate_arm_timer, s);
     return s;
 }

hw/timer/digic-timer.c

@@ -139,7 +139,7 @@ static void digic_timer_init(Object *obj)
 {
     DigicTimerState *s = DIGIC_TIMER(obj);
 
-    s->ptimer = ptimer_init(digic_timer_tick, NULL, PTIMER_POLICY_DEFAULT);
+    s->ptimer = ptimer_init(digic_timer_tick, NULL, PTIMER_POLICY_LEGACY);
 
     /*
      * FIXME: there is no documentation on Digic timer

hw/timer/etraxfs_timer.c

@@ -370,9 +370,9 @@ static void etraxfs_timer_realize(DeviceState *dev, Error **errp)
     ETRAXTimerState *t = ETRAX_TIMER(dev);
     SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
 
-    t->ptimer_t0 = ptimer_init(timer0_hit, t, PTIMER_POLICY_DEFAULT);
-    t->ptimer_t1 = ptimer_init(timer1_hit, t, PTIMER_POLICY_DEFAULT);
-    t->ptimer_wd = ptimer_init(watchdog_hit, t, PTIMER_POLICY_DEFAULT);
+    t->ptimer_t0 = ptimer_init(timer0_hit, t, PTIMER_POLICY_LEGACY);
+    t->ptimer_t1 = ptimer_init(timer1_hit, t, PTIMER_POLICY_LEGACY);
+    t->ptimer_wd = ptimer_init(watchdog_hit, t, PTIMER_POLICY_LEGACY);
 
     sysbus_init_irq(sbd, &t->irq);
     sysbus_init_irq(sbd, &t->nmi);

hw/timer/exynos4210_mct.c

@@ -1503,17 +1503,17 @@ static void exynos4210_mct_init(Object *obj)
 
     /* Global timer */
     s->g_timer.ptimer_frc = ptimer_init(exynos4210_gfrc_event, s,
-                                        PTIMER_POLICY_DEFAULT);
+                                        PTIMER_POLICY_LEGACY);
     memset(&s->g_timer.reg, 0, sizeof(struct gregs));
 
     /* Local timers */
     for (i = 0; i < 2; i++) {
         s->l_timer[i].tick_timer.ptimer_tick =
             ptimer_init(exynos4210_ltick_event, &s->l_timer[i],
-                        PTIMER_POLICY_DEFAULT);
+                        PTIMER_POLICY_LEGACY);
         s->l_timer[i].ptimer_frc =
             ptimer_init(exynos4210_lfrc_event, &s->l_timer[i],
-                        PTIMER_POLICY_DEFAULT);
+                        PTIMER_POLICY_LEGACY);
         s->l_timer[i].id = i;
     }
 

hw/timer/exynos4210_pwm.c

@@ -400,7 +400,7 @@ static void exynos4210_pwm_init(Object *obj)
         sysbus_init_irq(dev, &s->timer[i].irq);
         s->timer[i].ptimer = ptimer_init(exynos4210_pwm_tick,
                                          &s->timer[i],
-                                         PTIMER_POLICY_DEFAULT);
+                                         PTIMER_POLICY_LEGACY);
         s->timer[i].id = i;
         s->timer[i].parent = s;
     }

hw/timer/grlib_gptimer.c

@@ -383,7 +383,7 @@ static void grlib_gptimer_realize(DeviceState *dev, Error **errp)
 
         timer->unit   = unit;
         timer->ptimer = ptimer_init(grlib_gptimer_hit, timer,
-                                    PTIMER_POLICY_DEFAULT);
+                                    PTIMER_POLICY_LEGACY);
         timer->id     = i;
 
         /* One IRQ line for each timer */

hw/timer/imx_epit.c

@@ -347,9 +347,9 @@ static void imx_epit_realize(DeviceState *dev, Error **errp)
                           0x00001000);
     sysbus_init_mmio(sbd, &s->iomem);
 
-    s->timer_reload = ptimer_init(imx_epit_reload, s, PTIMER_POLICY_DEFAULT);
+    s->timer_reload = ptimer_init(imx_epit_reload, s, PTIMER_POLICY_LEGACY);
 
-    s->timer_cmp = ptimer_init(imx_epit_cmp, s, PTIMER_POLICY_DEFAULT);
+    s->timer_cmp = ptimer_init(imx_epit_cmp, s, PTIMER_POLICY_LEGACY);
 }
 
 static void imx_epit_class_init(ObjectClass *klass, void *data)

hw/timer/imx_gpt.c

@@ -505,7 +505,7 @@ static void imx_gpt_realize(DeviceState *dev, Error **errp)
                           0x00001000);
     sysbus_init_mmio(sbd, &s->iomem);
 
-    s->timer = ptimer_init(imx_gpt_timeout, s, PTIMER_POLICY_DEFAULT);
+    s->timer = ptimer_init(imx_gpt_timeout, s, PTIMER_POLICY_LEGACY);
 }
 
 static void imx_gpt_class_init(ObjectClass *klass, void *data)

hw/timer/mss-timer.c

@@ -232,7 +232,7 @@ static void mss_timer_init(Object *obj)
     for (i = 0; i < NUM_TIMERS; i++) {
         struct Msf2Timer *st = &t->timers[i];
 
-        st->ptimer = ptimer_init(timer_hit, st, PTIMER_POLICY_DEFAULT);
+        st->ptimer = ptimer_init(timer_hit, st, PTIMER_POLICY_LEGACY);
         ptimer_transaction_begin(st->ptimer);
         ptimer_set_freq(st->ptimer, t->freq_hz);
         ptimer_transaction_commit(st->ptimer);

hw/timer/sh_timer.c

@@ -239,7 +239,7 @@ static void *sh_timer_init(uint32_t freq, int feat, qemu_irq irq)
     s->enabled = 0;
     s->irq = irq;
 
-    s->timer = ptimer_init(sh_timer_tick, s, PTIMER_POLICY_DEFAULT);
+    s->timer = ptimer_init(sh_timer_tick, s, PTIMER_POLICY_LEGACY);
 
     sh_timer_write(s, OFFSET_TCOR >> 2, s->tcor);
     sh_timer_write(s, OFFSET_TCNT >> 2, s->tcnt);

hw/timer/slavio_timer.c

@@ -405,7 +405,7 @@ static void slavio_timer_init(Object *obj)
         tc->timer_index = i;
 
         s->cputimer[i].timer = ptimer_init(slavio_timer_irq, tc,
-                                           PTIMER_POLICY_DEFAULT);
+                                           PTIMER_POLICY_LEGACY);
         ptimer_transaction_begin(s->cputimer[i].timer);
         ptimer_set_period(s->cputimer[i].timer, TIMER_PERIOD);
         ptimer_transaction_commit(s->cputimer[i].timer);

hw/timer/xilinx_timer.c

@@ -223,7 +223,7 @@ static void xilinx_timer_realize(DeviceState *dev, Error **errp)
 
         xt->parent = t;
         xt->nr = i;
-        xt->ptimer = ptimer_init(timer_hit, xt, PTIMER_POLICY_DEFAULT);
+        xt->ptimer = ptimer_init(timer_hit, xt, PTIMER_POLICY_LEGACY);
         ptimer_transaction_begin(xt->ptimer);
         ptimer_set_freq(xt->ptimer, t->freq_hz);
         ptimer_transaction_commit(xt->ptimer);

include/hw/ptimer.h

@@ -33,9 +33,17 @@
  * to stderr when the guest attempts to enable the timer.
  */
 
-/* The default ptimer policy retains backward compatibility with the legacy
- * timers. Custom policies are adjusting the default one. Consider providing
- * a correct policy for your timer.
+/*
+ * The 'legacy' ptimer policy retains backward compatibility with the
+ * traditional ptimer behaviour from before policy flags were introduced.
+ * It has several weird behaviours which don't match typical hardware
+ * timer behaviour. For a new device using ptimers, you should not
+ * use PTIMER_POLICY_LEGACY, but instead check the actual behaviour
+ * that you need and specify the right set of policy flags to get that.
+ *
+ * If you are overhauling an existing device that uses PTIMER_POLICY_LEGACY
+ * and are in a position to check or test the real hardware behaviour,
+ * consider updating it to specify the right policy flags.
  *
  * The rough edges of the default policy:
  *  - Starting to run with a period = 0 emits error message and stops the
@@ -54,7 +62,7 @@
  *    since the last period, effectively restarting the timer with a
  *    counter = counter value at the moment of change (.i.e. one less).
  */
-#define PTIMER_POLICY_DEFAULT               0
+#define PTIMER_POLICY_LEGACY                0
 
 /* Periodic timer counter stays with "0" for a one period before wrapping
  * around.  */

tests/unit/ptimer-test.c

@@ -768,8 +768,8 @@ static void add_ptimer_tests(uint8_t policy)
     char policy_name[256] = "";
     char *tmp;
 
-    if (policy == PTIMER_POLICY_DEFAULT) {
-        g_sprintf(policy_name, "default");
+    if (policy == PTIMER_POLICY_LEGACY) {
+        g_sprintf(policy_name, "legacy");
     }
 
     if (policy & PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD) {
@@ -862,7 +862,7 @@ static void add_ptimer_tests(uint8_t policy)
 static void add_all_ptimer_policies_comb_tests(void)
 {
     int last_policy = PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT;
-    int policy = PTIMER_POLICY_DEFAULT;
+    int policy = PTIMER_POLICY_LEGACY;
 
     for (; policy < (last_policy << 1); policy++) {
         if ((policy & PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT) &&