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 "exec/replay-core.h"
  14 #include "sysemu/cpu-timers.h"
  15 #include "sysemu/qtest.h"
  16 #include "block/aio.h"
  17 #include "hw/clock.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 (s->enabled == 0) {
 121             /* trigger callback disabled the timer already */
 122             return;
 123         }
 124         if (!qtest_enabled()) {
 125             fprintf(stderr, "Timer with delta zero, disabling\n");
 126         }
 127         timer_del(s->timer);
 128         s->enabled = 0;
 129         return;
 130     }
 131
 132     /*
 133      * Artificially limit timeout rate to something
 134      * achievable under QEMU.  Otherwise, QEMU spends all
 135      * its time generating timer interrupts, and there
 136      * is no forward progress.
 137      * About ten microseconds is the fastest that really works
 138      * on the current generation of host machines.
 139      */
 140
 141     if (s->enabled == 1 && (delta * period < 10000) &&
 142         !icount_enabled() && !qtest_enabled()) {
 143         period = 10000 / delta;
 144         period_frac = 0;
 145     }
 146
 147     s->last_event = s->next_event;
 148     s->next_event = s->last_event + delta * period;
 149     if (period_frac) {
 150         s->next_event += ((int64_t)period_frac * delta) >> 32;
 151     }
 152     timer_mod(s->timer, s->next_event);
 153 }
 154
 155 static void ptimer_tick(void *opaque)
 156 {
 157     ptimer_state *s = (ptimer_state *)opaque;
 158     bool trigger = true;
 159
 160     /*
 161      * We perform all the tick actions within a begin/commit block
 162      * because the callback function that ptimer_trigger() calls
 163      * might make calls into the ptimer APIs that provoke another
 164      * trigger, and we want that to cause the callback function
 165      * to be called iteratively, not recursively.
 166      */
 167     ptimer_transaction_begin(s);
 168
 169     if (s->enabled == 2) {
 170         s->delta = 0;
 171         s->enabled = 0;
 172     } else {
 173         int delta_adjust = DELTA_ADJUST;
 174
 175         if (s->delta == 0 || s->limit == 0) {
 176             /* If a "continuous trigger" policy is not used and limit == 0,
 177                we should error out. delta == 0 means that this tick is
 178                caused by a "no immediate reload" policy, so it shouldn't
 179                be adjusted.  */
 180             delta_adjust = DELTA_NO_ADJUST;
 181         }
 182
 183         if (!(s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)) {
 184             /* Avoid re-trigger on deferred reload if "no immediate trigger"
 185                policy isn't used.  */
 186             trigger = (delta_adjust == DELTA_ADJUST);
 187         }
 188
 189         s->delta = s->limit;
 190
 191         ptimer_reload(s, delta_adjust);
 192     }
 193
 194     if (trigger) {
 195         ptimer_trigger(s);
 196     }
 197
 198     ptimer_transaction_commit(s);
 199 }
 200
 201 uint64_t ptimer_get_count(ptimer_state *s)
 202 {
 203     uint64_t counter;
 204
 205     if (s->enabled && s->delta != 0) {
 206         int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 207         int64_t next = s->next_event;
 208         int64_t last = s->last_event;
 209         bool expired = (now - next >= 0);
 210         bool oneshot = (s->enabled == 2);
 211
 212         /* Figure out the current counter value.  */
 213         if (expired) {
 214             /* Prevent timer underflowing if it should already have
 215                triggered.  */
 216             counter = 0;
 217         } else {
 218             uint64_t rem;
 219             uint64_t div;
 220             int clz1, clz2;
 221             int shift;
 222             uint32_t period_frac = s->period_frac;
 223             uint64_t period = s->period;
 224
 225             if (!oneshot && (s->delta * period < 10000) &&
 226                 !icount_enabled() && !qtest_enabled()) {
 227                 period = 10000 / s->delta;
 228                 period_frac = 0;
 229             }
 230
 231             /* We need to divide time by period, where time is stored in
 232                rem (64-bit integer) and period is stored in period/period_frac
 233                (64.32 fixed point).
 234
 235                Doing full precision division is hard, so scale values and
 236                do a 64-bit division.  The result should be rounded down,
 237                so that the rounding error never causes the timer to go
 238                backwards.
 239             */
 240
 241             rem = next - now;
 242             div = period;
 243
 244             clz1 = clz64(rem);
 245             clz2 = clz64(div);
 246             shift = clz1 < clz2 ? clz1 : clz2;
 247
 248             rem <<= shift;
 249             div <<= shift;
 250             if (shift >= 32) {
 251                 div |= ((uint64_t)period_frac << (shift - 32));
 252             } else {
 253                 if (shift != 0)
 254                     div |= (period_frac >> (32 - shift));
 255                 /* Look at remaining bits of period_frac and round div up if
 256                    necessary.  */
 257                 if ((uint32_t)(period_frac << shift))
 258                     div += 1;
 259             }
 260             counter = rem / div;
 261
 262             if (s->policy_mask & PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD) {
 263                 /* Before wrapping around, timer should stay with counter = 0
 264                    for a one period.  */
 265                 if (!oneshot && s->delta == s->limit) {
 266                     if (now == last) {
 267                         /* Counter == delta here, check whether it was
 268                            adjusted and if it was, then right now it is
 269                            that "one period".  */
 270                         if (counter == s->limit + DELTA_ADJUST) {
 271                             return 0;
 272                         }
 273                     } else if (counter == s->limit) {
 274                         /* Since the counter is rounded down and now != last,
 275                            the counter == limit means that delta was adjusted
 276                            by +1 and right now it is that adjusted period.  */
 277                         return 0;
 278                     }
 279                 }
 280             }
 281         }
 282
 283         if (s->policy_mask & PTIMER_POLICY_NO_COUNTER_ROUND_DOWN) {
 284             /* If now == last then delta == limit, i.e. the counter already
 285                represents the correct value. It would be rounded down a 1ns
 286                later.  */
 287             if (now != last) {
 288                 counter += 1;
 289             }
 290         }
 291     } else {
 292         counter = s->delta;
 293     }
 294     return counter;
 295 }
 296
 297 void ptimer_set_count(ptimer_state *s, uint64_t count)
 298 {
 299     assert(s->in_transaction);
 300     s->delta = count;
 301     if (s->enabled) {
 302         s->need_reload = true;
 303     }
 304 }
 305
 306 void ptimer_run(ptimer_state *s, int oneshot)
 307 {
 308     bool was_disabled = !s->enabled;
 309
 310     assert(s->in_transaction);
 311
 312     if (was_disabled && s->period == 0) {
 313         if (!qtest_enabled()) {
 314             fprintf(stderr, "Timer with period zero, disabling\n");
 315         }
 316         return;
 317     }
 318     s->enabled = oneshot ? 2 : 1;
 319     if (was_disabled) {
 320         s->need_reload = true;
 321     }
 322 }
 323
 324 /* Pause a timer.  Note that this may cause it to "lose" time, even if it
 325    is immediately restarted.  */
 326 void ptimer_stop(ptimer_state *s)
 327 {
 328     assert(s->in_transaction);
 329
 330     if (!s->enabled)
 331         return;
 332
 333     s->delta = ptimer_get_count(s);
 334     timer_del(s->timer);
 335     s->enabled = 0;
 336     s->need_reload = false;
 337 }
 338
 339 /* Set counter increment interval in nanoseconds.  */
 340 void ptimer_set_period(ptimer_state *s, int64_t period)
 341 {
 342     assert(s->in_transaction);
 343     s->delta = ptimer_get_count(s);
 344     s->period = period;
 345     s->period_frac = 0;
 346     if (s->enabled) {
 347         s->need_reload = true;
 348     }
 349 }
 350
 351 /* Set counter increment interval from a Clock */
 352 void ptimer_set_period_from_clock(ptimer_state *s, const Clock *clk,
 353                                   unsigned int divisor)
 354 {
 355     /*
 356      * The raw clock period is a 64-bit value in units of 2^-32 ns;
 357      * put another way it's a 32.32 fixed-point ns value. Our internal
 358      * representation of the period is 64.32 fixed point ns, so
 359      * the conversion is simple.
 360      */
 361     uint64_t raw_period = clock_get(clk);
 362     uint64_t period_frac;
 363
 364     assert(s->in_transaction);
 365     s->delta = ptimer_get_count(s);
 366     s->period = extract64(raw_period, 32, 32);
 367     period_frac = extract64(raw_period, 0, 32);
 368     /*
 369      * divisor specifies a possible frequency divisor between the
 370      * clock and the timer, so it is a multiplier on the period.
 371      * We do the multiply after splitting the raw period out into
 372      * period and frac to avoid having to do a 32*64->96 multiply.
 373      */
 374     s->period *= divisor;
 375     period_frac *= divisor;
 376     s->period += extract64(period_frac, 32, 32);
 377     s->period_frac = (uint32_t)period_frac;
 378
 379     if (s->enabled) {
 380         s->need_reload = true;
 381     }
 382 }
 383
 384 /* Set counter frequency in Hz.  */
 385 void ptimer_set_freq(ptimer_state *s, uint32_t freq)
 386 {
 387     assert(s->in_transaction);
 388     s->delta = ptimer_get_count(s);
 389     s->period = 1000000000ll / freq;
 390     s->period_frac = (1000000000ll << 32) / freq;
 391     if (s->enabled) {
 392         s->need_reload = true;
 393     }
 394 }
 395
 396 /* Set the initial countdown value.  If reload is nonzero then also set
 397    count = limit.  */
 398 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload)
 399 {
 400     assert(s->in_transaction);
 401     s->limit = limit;
 402     if (reload)
 403         s->delta = limit;
 404     if (s->enabled && reload) {
 405         s->need_reload = true;
 406     }
 407 }
 408
 409 uint64_t ptimer_get_limit(ptimer_state *s)
 410 {
 411     return s->limit;
 412 }
 413
 414 void ptimer_transaction_begin(ptimer_state *s)
 415 {
 416     assert(!s->in_transaction);
 417     s->in_transaction = true;
 418     s->need_reload = false;
 419 }
 420
 421 void ptimer_transaction_commit(ptimer_state *s)
 422 {
 423     assert(s->in_transaction);
 424     /*
 425      * We must loop here because ptimer_reload() can call the callback
 426      * function, which might then update ptimer state in a way that
 427      * means we need to do another reload and possibly another callback.
 428      * A disabled timer never needs reloading (and if we don't check
 429      * this then we loop forever if ptimer_reload() disables the timer).
 430      */
 431     while (s->need_reload && s->enabled) {
 432         s->need_reload = false;
 433         s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 434         ptimer_reload(s, 0);
 435     }
 436     /* Now we've finished reload we can leave the transaction block. */
 437     s->in_transaction = false;
 438 }
 439
 440 const VMStateDescription vmstate_ptimer = {
 441     .name = "ptimer",
 442     .version_id = 1,
 443     .minimum_version_id = 1,
 444     .fields = (const VMStateField[]) {
 445         VMSTATE_UINT8(enabled, ptimer_state),
 446         VMSTATE_UINT64(limit, ptimer_state),
 447         VMSTATE_UINT64(delta, ptimer_state),
 448         VMSTATE_UINT32(period_frac, ptimer_state),
 449         VMSTATE_INT64(period, ptimer_state),
 450         VMSTATE_INT64(last_event, ptimer_state),
 451         VMSTATE_INT64(next_event, ptimer_state),
 452         VMSTATE_TIMER_PTR(timer, ptimer_state),
 453         VMSTATE_END_OF_LIST()
 454     }
 455 };
 456
 457 ptimer_state *ptimer_init(ptimer_cb callback, void *callback_opaque,
 458                           uint8_t policy_mask)
 459 {
 460     ptimer_state *s;
 461
 462     /* The callback function is mandatory. */
 463     assert(callback);
 464
 465     s = g_new0(ptimer_state, 1);
 466     s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, ptimer_tick, s);
 467     s->policy_mask = policy_mask;
 468     s->callback = callback;
 469     s->callback_opaque = callback_opaque;
 470
 471     /*
 472      * These two policies are incompatible -- trigger-on-decrement implies
 473      * a timer trigger when the count becomes 0, but no-immediate-trigger
 474      * implies a trigger when the count stops being 0.
 475      */
 476     assert(!((policy_mask & PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT) &&
 477              (policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)));
 478     return s;
 479 }
 480
 481 void ptimer_free(ptimer_state *s)
 482 {
 483     timer_free(s->timer);
 484     g_free(s);
 485 }