hw/core/ptimer.c

   1 /*
   2  * General purpose implementation of a simple periodic countdown timer.
   3  *
   4  * Copyright (c) 2007 CodeSourcery.
   5  *
   6  * This code is licensed under the GNU LGPL.
   7  */
   8
   9 #include "qemu/osdep.h"
  10 #include "hw/ptimer.h"
  11 #include "migration/vmstate.h"
  12 #include "qemu/host-utils.h"
  13 #include "sysemu/replay.h"
  14 #include "sysemu/cpu-timers.h"
  15 #include "sysemu/qtest.h"
  16 #include "block/aio.h"
  17 #include "sysemu/cpus.h"
  18
  19 #define DELTA_ADJUST     1
  20 #define DELTA_NO_ADJUST -1
  21
  22 struct ptimer_state
  23 {
  24     uint8_t enabled; /* 0 = disabled, 1 = periodic, 2 = oneshot.  */
  25     uint64_t limit;
  26     uint64_t delta;
  27     uint32_t period_frac;
  28     int64_t period;
  29     int64_t last_event;
  30     int64_t next_event;
  31     uint8_t policy_mask;
  32     QEMUTimer *timer;
  33     ptimer_cb callback;
  34     void *callback_opaque;
  35     /*
  36      * These track whether we're in a transaction block, and if we
  37      * need to do a timer reload when the block finishes. They don't
  38      * need to be migrated because migration can never happen in the
  39      * middle of a transaction block.
  40      */
  41     bool in_transaction;
  42     bool need_reload;
  43 };
  44
  45 /* Use a bottom-half routine to avoid reentrancy issues.  */
  46 static void ptimer_trigger(ptimer_state *s)
  47 {
  48     s->callback(s->callback_opaque);
  49 }
  50
  51 static void ptimer_reload(ptimer_state *s, int delta_adjust)
  52 {
  53     uint32_t period_frac;
  54     uint64_t period;
  55     uint64_t delta;
  56     bool suppress_trigger = false;
  57
  58     /*
  59      * Note that if delta_adjust is 0 then we must be here because of
  60      * a count register write or timer start, not because of timer expiry.
  61      * In that case the policy might require us to suppress the timer trigger
  62      * that we would otherwise generate for a zero delta.
  63      */
  64     if (delta_adjust == 0 &&
  65         (s->policy_mask & PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT)) {
  66         suppress_trigger = true;
  67     }
  68     if (s->delta == 0 && !(s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)
  69         && !suppress_trigger) {
  70         ptimer_trigger(s);
  71     }
  72
  73     /*
  74      * Note that ptimer_trigger() might call the device callback function,
  75      * which can then modify timer state, so we must not cache any fields
  76      * from ptimer_state until after we have called it.
  77      */
  78     delta = s->delta;
  79     period = s->period;
  80     period_frac = s->period_frac;
  81
  82     if (delta == 0 && !(s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_RELOAD)) {
  83         delta = s->delta = s->limit;
  84     }
  85
  86     if (s->period == 0) {
  87         if (!qtest_enabled()) {
  88             fprintf(stderr, "Timer with period zero, disabling\n");
  89         }
  90         timer_del(s->timer);
  91         s->enabled = 0;
  92         return;
  93     }
  94
  95     if (s->policy_mask & PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD) {
  96         if (delta_adjust != DELTA_NO_ADJUST) {
  97             delta += delta_adjust;
  98         }
  99     }
 100
 101     if (delta == 0 && (s->policy_mask & PTIMER_POLICY_CONTINUOUS_TRIGGER)) {
 102         if (s->enabled == 1 && s->limit == 0) {
 103             delta = 1;
 104         }
 105     }
 106
 107     if (delta == 0 && (s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)) {
 108         if (delta_adjust != DELTA_NO_ADJUST) {
 109             delta = 1;
 110         }
 111     }
 112
 113     if (delta == 0 && (s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_RELOAD)) {
 114         if (s->enabled == 1 && s->limit != 0) {
 115             delta = 1;
 116         }
 117     }
 118
 119     if (delta == 0) {
 120         if (!qtest_enabled()) {
 121             fprintf(stderr, "Timer with delta zero, disabling\n");
 122         }
 123         timer_del(s->timer);
 124         s->enabled = 0;
 125         return;
 126     }
 127
 128     /*
 129      * Artificially limit timeout rate to something
 130      * achievable under QEMU.  Otherwise, QEMU spends all
 131      * its time generating timer interrupts, and there
 132      * is no forward progress.
 133      * About ten microseconds is the fastest that really works
 134      * on the current generation of host machines.
 135      */
 136
 137     if (s->enabled == 1 && (delta * period < 10000) &&
 138         !icount_enabled() && !qtest_enabled()) {
 139         period = 10000 / delta;
 140         period_frac = 0;
 141     }
 142
 143     s->last_event = s->next_event;
 144     s->next_event = s->last_event + delta * period;
 145     if (period_frac) {
 146         s->next_event += ((int64_t)period_frac * delta) >> 32;
 147     }
 148     timer_mod(s->timer, s->next_event);
 149 }
 150
 151 static void ptimer_tick(void *opaque)
 152 {
 153     ptimer_state *s = (ptimer_state *)opaque;
 154     bool trigger = true;
 155
 156     /*
 157      * We perform all the tick actions within a begin/commit block
 158      * because the callback function that ptimer_trigger() calls
 159      * might make calls into the ptimer APIs that provoke another
 160      * trigger, and we want that to cause the callback function
 161      * to be called iteratively, not recursively.
 162      */
 163     ptimer_transaction_begin(s);
 164
 165     if (s->enabled == 2) {
 166         s->delta = 0;
 167         s->enabled = 0;
 168     } else {
 169         int delta_adjust = DELTA_ADJUST;
 170
 171         if (s->delta == 0 || s->limit == 0) {
 172             /* If a "continuous trigger" policy is not used and limit == 0,
 173                we should error out. delta == 0 means that this tick is
 174                caused by a "no immediate reload" policy, so it shouldn't
 175                be adjusted.  */
 176             delta_adjust = DELTA_NO_ADJUST;
 177         }
 178
 179         if (!(s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)) {
 180             /* Avoid re-trigger on deferred reload if "no immediate trigger"
 181                policy isn't used.  */
 182             trigger = (delta_adjust == DELTA_ADJUST);
 183         }
 184
 185         s->delta = s->limit;
 186
 187         ptimer_reload(s, delta_adjust);
 188     }
 189
 190     if (trigger) {
 191         ptimer_trigger(s);
 192     }
 193
 194     ptimer_transaction_commit(s);
 195 }
 196
 197 uint64_t ptimer_get_count(ptimer_state *s)
 198 {
 199     uint64_t counter;
 200
 201     if (s->enabled && s->delta != 0) {
 202         int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 203         int64_t next = s->next_event;
 204         int64_t last = s->last_event;
 205         bool expired = (now - next >= 0);
 206         bool oneshot = (s->enabled == 2);
 207
 208         /* Figure out the current counter value.  */
 209         if (expired) {
 210             /* Prevent timer underflowing if it should already have
 211                triggered.  */
 212             counter = 0;
 213         } else {
 214             uint64_t rem;
 215             uint64_t div;
 216             int clz1, clz2;
 217             int shift;
 218             uint32_t period_frac = s->period_frac;
 219             uint64_t period = s->period;
 220
 221             if (!oneshot && (s->delta * period < 10000) &&
 222                 !icount_enabled() && !qtest_enabled()) {
 223                 period = 10000 / s->delta;
 224                 period_frac = 0;
 225             }
 226
 227             /* We need to divide time by period, where time is stored in
 228                rem (64-bit integer) and period is stored in period/period_frac
 229                (64.32 fixed point).
 230
 231                Doing full precision division is hard, so scale values and
 232                do a 64-bit division.  The result should be rounded down,
 233                so that the rounding error never causes the timer to go
 234                backwards.
 235             */
 236
 237             rem = next - now;
 238             div = period;
 239
 240             clz1 = clz64(rem);
 241             clz2 = clz64(div);
 242             shift = clz1 < clz2 ? clz1 : clz2;
 243
 244             rem <<= shift;
 245             div <<= shift;
 246             if (shift >= 32) {
 247                 div |= ((uint64_t)period_frac << (shift - 32));
 248             } else {
 249                 if (shift != 0)
 250                     div |= (period_frac >> (32 - shift));
 251                 /* Look at remaining bits of period_frac and round div up if
 252                    necessary.  */
 253                 if ((uint32_t)(period_frac << shift))
 254                     div += 1;
 255             }
 256             counter = rem / div;
 257
 258             if (s->policy_mask & PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD) {
 259                 /* Before wrapping around, timer should stay with counter = 0
 260                    for a one period.  */
 261                 if (!oneshot && s->delta == s->limit) {
 262                     if (now == last) {
 263                         /* Counter == delta here, check whether it was
 264                            adjusted and if it was, then right now it is
 265                            that "one period".  */
 266                         if (counter == s->limit + DELTA_ADJUST) {
 267                             return 0;
 268                         }
 269                     } else if (counter == s->limit) {
 270                         /* Since the counter is rounded down and now != last,
 271                            the counter == limit means that delta was adjusted
 272                            by +1 and right now it is that adjusted period.  */
 273                         return 0;
 274                     }
 275                 }
 276             }
 277         }
 278
 279         if (s->policy_mask & PTIMER_POLICY_NO_COUNTER_ROUND_DOWN) {
 280             /* If now == last then delta == limit, i.e. the counter already
 281                represents the correct value. It would be rounded down a 1ns
 282                later.  */
 283             if (now != last) {
 284                 counter += 1;
 285             }
 286         }
 287     } else {
 288         counter = s->delta;
 289     }
 290     return counter;
 291 }
 292
 293 void ptimer_set_count(ptimer_state *s, uint64_t count)
 294 {
 295     assert(s->in_transaction);
 296     s->delta = count;
 297     if (s->enabled) {
 298         s->need_reload = true;
 299     }
 300 }
 301
 302 void ptimer_run(ptimer_state *s, int oneshot)
 303 {
 304     bool was_disabled = !s->enabled;
 305
 306     assert(s->in_transaction);
 307
 308     if (was_disabled && s->period == 0) {
 309         if (!qtest_enabled()) {
 310             fprintf(stderr, "Timer with period zero, disabling\n");
 311         }
 312         return;
 313     }
 314     s->enabled = oneshot ? 2 : 1;
 315     if (was_disabled) {
 316         s->need_reload = true;
 317     }
 318 }
 319
 320 /* Pause a timer.  Note that this may cause it to "lose" time, even if it
 321    is immediately restarted.  */
 322 void ptimer_stop(ptimer_state *s)
 323 {
 324     assert(s->in_transaction);
 325
 326     if (!s->enabled)
 327         return;
 328
 329     s->delta = ptimer_get_count(s);
 330     timer_del(s->timer);
 331     s->enabled = 0;
 332     s->need_reload = false;
 333 }
 334
 335 /* Set counter increment interval in nanoseconds.  */
 336 void ptimer_set_period(ptimer_state *s, int64_t period)
 337 {
 338     assert(s->in_transaction);
 339     s->delta = ptimer_get_count(s);
 340     s->period = period;
 341     s->period_frac = 0;
 342     if (s->enabled) {
 343         s->need_reload = true;
 344     }
 345 }
 346
 347 /* Set counter frequency in Hz.  */
 348 void ptimer_set_freq(ptimer_state *s, uint32_t freq)
 349 {
 350     assert(s->in_transaction);
 351     s->delta = ptimer_get_count(s);
 352     s->period = 1000000000ll / freq;
 353     s->period_frac = (1000000000ll << 32) / freq;
 354     if (s->enabled) {
 355         s->need_reload = true;
 356     }
 357 }
 358
 359 /* Set the initial countdown value.  If reload is nonzero then also set
 360    count = limit.  */
 361 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload)
 362 {
 363     assert(s->in_transaction);
 364     s->limit = limit;
 365     if (reload)
 366         s->delta = limit;
 367     if (s->enabled && reload) {
 368         s->need_reload = true;
 369     }
 370 }
 371
 372 uint64_t ptimer_get_limit(ptimer_state *s)
 373 {
 374     return s->limit;
 375 }
 376
 377 void ptimer_transaction_begin(ptimer_state *s)
 378 {
 379     assert(!s->in_transaction);
 380     s->in_transaction = true;
 381     s->need_reload = false;
 382 }
 383
 384 void ptimer_transaction_commit(ptimer_state *s)
 385 {
 386     assert(s->in_transaction);
 387     /*
 388      * We must loop here because ptimer_reload() can call the callback
 389      * function, which might then update ptimer state in a way that
 390      * means we need to do another reload and possibly another callback.
 391      * A disabled timer never needs reloading (and if we don't check
 392      * this then we loop forever if ptimer_reload() disables the timer).
 393      */
 394     while (s->need_reload && s->enabled) {
 395         s->need_reload = false;
 396         s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 397         ptimer_reload(s, 0);
 398     }
 399     /* Now we've finished reload we can leave the transaction block. */
 400     s->in_transaction = false;
 401 }
 402
 403 const VMStateDescription vmstate_ptimer = {
 404     .name = "ptimer",
 405     .version_id = 1,
 406     .minimum_version_id = 1,
 407     .fields = (VMStateField[]) {
 408         VMSTATE_UINT8(enabled, ptimer_state),
 409         VMSTATE_UINT64(limit, ptimer_state),
 410         VMSTATE_UINT64(delta, ptimer_state),
 411         VMSTATE_UINT32(period_frac, ptimer_state),
 412         VMSTATE_INT64(period, ptimer_state),
 413         VMSTATE_INT64(last_event, ptimer_state),
 414         VMSTATE_INT64(next_event, ptimer_state),
 415         VMSTATE_TIMER_PTR(timer, ptimer_state),
 416         VMSTATE_END_OF_LIST()
 417     }
 418 };
 419
 420 ptimer_state *ptimer_init(ptimer_cb callback, void *callback_opaque,
 421                           uint8_t policy_mask)
 422 {
 423     ptimer_state *s;
 424
 425     /* The callback function is mandatory. */
 426     assert(callback);
 427
 428     s = g_new0(ptimer_state, 1);
 429     s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, ptimer_tick, s);
 430     s->policy_mask = policy_mask;
 431     s->callback = callback;
 432     s->callback_opaque = callback_opaque;
 433
 434     /*
 435      * These two policies are incompatible -- trigger-on-decrement implies
 436      * a timer trigger when the count becomes 0, but no-immediate-trigger
 437      * implies a trigger when the count stops being 0.
 438      */
 439     assert(!((policy_mask & PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT) &&
 440              (policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)));
 441     return s;
 442 }
 443
 444 void ptimer_free(ptimer_state *s)
 445 {
 446     timer_free(s->timer);
 447     g_free(s);
 448 }