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