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 #include "hw/clock.h"
  19
  20 #define DELTA_ADJUST     1
  21 #define DELTA_NO_ADJUST -1
  22
  23 struct ptimer_state
  24 {
  25     uint8_t enabled; /* 0 = disabled, 1 = periodic, 2 = oneshot.  */
  26     uint64_t limit;
  27     uint64_t delta;
  28     uint32_t period_frac;
  29     int64_t period;
  30     int64_t last_event;
  31     int64_t next_event;
  32     uint8_t policy_mask;
  33     QEMUTimer *timer;
  34     ptimer_cb callback;
  35     void *callback_opaque;
  36     /*
  37      * These track whether we're in a transaction block, and if we
  38      * need to do a timer reload when the block finishes. They don't
  39      * need to be migrated because migration can never happen in the
  40      * middle of a transaction block.
  41      */
  42     bool in_transaction;
  43     bool need_reload;
  44 };
  45
  46 /* Use a bottom-half routine to avoid reentrancy issues.  */
  47 static void ptimer_trigger(ptimer_state *s)
  48 {
  49     s->callback(s->callback_opaque);
  50 }
  51
  52 static void ptimer_reload(ptimer_state *s, int delta_adjust)
  53 {
  54     uint32_t period_frac;
  55     uint64_t period;
  56     uint64_t delta;
  57     bool suppress_trigger = false;
  58
  59     /*
  60      * Note that if delta_adjust is 0 then we must be here because of
  61      * a count register write or timer start, not because of timer expiry.
  62      * In that case the policy might require us to suppress the timer trigger
  63      * that we would otherwise generate for a zero delta.
  64      */
  65     if (delta_adjust == 0 &&
  66         (s->policy_mask & PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT)) {
  67         suppress_trigger = true;
  68     }
  69     if (s->delta == 0 && !(s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)
  70         && !suppress_trigger) {
  71         ptimer_trigger(s);
  72     }
  73
  74     /*
  75      * Note that ptimer_trigger() might call the device callback function,
  76      * which can then modify timer state, so we must not cache any fields
  77      * from ptimer_state until after we have called it.
  78      */
  79     delta = s->delta;
  80     period = s->period;
  81     period_frac = s->period_frac;
  82
  83     if (delta == 0 && !(s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_RELOAD)) {
  84         delta = s->delta = s->limit;
  85     }
  86
  87     if (s->period == 0) {
  88         if (!qtest_enabled()) {
  89             fprintf(stderr, "Timer with period zero, disabling\n");
  90         }
  91         timer_del(s->timer);
  92         s->enabled = 0;
  93         return;
  94     }
  95
  96     if (s->policy_mask & PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD) {
  97         if (delta_adjust != DELTA_NO_ADJUST) {
  98             delta += delta_adjust;
  99         }
 100     }
 101
 102     if (delta == 0 && (s->policy_mask & PTIMER_POLICY_CONTINUOUS_TRIGGER)) {
 103         if (s->enabled == 1 && s->limit == 0) {
 104             delta = 1;
 105         }
 106     }
 107
 108     if (delta == 0 && (s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)) {
 109         if (delta_adjust != DELTA_NO_ADJUST) {
 110             delta = 1;
 111         }
 112     }
 113
 114     if (delta == 0 && (s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_RELOAD)) {
 115         if (s->enabled == 1 && s->limit != 0) {
 116             delta = 1;
 117         }
 118     }
 119
 120     if (delta == 0) {
 121         if (s->enabled == 0) {
 122             /* trigger callback disabled the timer already */
 123             return;
 124         }
 125         if (!qtest_enabled()) {
 126             fprintf(stderr, "Timer with delta zero, disabling\n");
 127         }
 128         timer_del(s->timer);
 129         s->enabled = 0;
 130         return;
 131     }
 132
 133     /*
 134      * Artificially limit timeout rate to something
 135      * achievable under QEMU.  Otherwise, QEMU spends all
 136      * its time generating timer interrupts, and there
 137      * is no forward progress.
 138      * About ten microseconds is the fastest that really works
 139      * on the current generation of host machines.
 140      */
 141
 142     if (s->enabled == 1 && (delta * period < 10000) &&
 143         !icount_enabled() && !qtest_enabled()) {
 144         period = 10000 / delta;
 145         period_frac = 0;
 146     }
 147
 148     s->last_event = s->next_event;
 149     s->next_event = s->last_event + delta * period;
 150     if (period_frac) {
 151         s->next_event += ((int64_t)period_frac * delta) >> 32;
 152     }
 153     timer_mod(s->timer, s->next_event);
 154 }
 155
 156 static void ptimer_tick(void *opaque)
 157 {
 158     ptimer_state *s = (ptimer_state *)opaque;
 159     bool trigger = true;
 160
 161     /*
 162      * We perform all the tick actions within a begin/commit block
 163      * because the callback function that ptimer_trigger() calls
 164      * might make calls into the ptimer APIs that provoke another
 165      * trigger, and we want that to cause the callback function
 166      * to be called iteratively, not recursively.
 167      */
 168     ptimer_transaction_begin(s);
 169
 170     if (s->enabled == 2) {
 171         s->delta = 0;
 172         s->enabled = 0;
 173     } else {
 174         int delta_adjust = DELTA_ADJUST;
 175
 176         if (s->delta == 0 || s->limit == 0) {
 177             /* If a "continuous trigger" policy is not used and limit == 0,
 178                we should error out. delta == 0 means that this tick is
 179                caused by a "no immediate reload" policy, so it shouldn't
 180                be adjusted.  */
 181             delta_adjust = DELTA_NO_ADJUST;
 182         }
 183
 184         if (!(s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)) {
 185             /* Avoid re-trigger on deferred reload if "no immediate trigger"
 186                policy isn't used.  */
 187             trigger = (delta_adjust == DELTA_ADJUST);
 188         }
 189
 190         s->delta = s->limit;
 191
 192         ptimer_reload(s, delta_adjust);
 193     }
 194
 195     if (trigger) {
 196         ptimer_trigger(s);
 197     }
 198
 199     ptimer_transaction_commit(s);
 200 }
 201
 202 uint64_t ptimer_get_count(ptimer_state *s)
 203 {
 204     uint64_t counter;
 205
 206     if (s->enabled && s->delta != 0) {
 207         int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 208         int64_t next = s->next_event;
 209         int64_t last = s->last_event;
 210         bool expired = (now - next >= 0);
 211         bool oneshot = (s->enabled == 2);
 212
 213         /* Figure out the current counter value.  */
 214         if (expired) {
 215             /* Prevent timer underflowing if it should already have
 216                triggered.  */
 217             counter = 0;
 218         } else {
 219             uint64_t rem;
 220             uint64_t div;
 221             int clz1, clz2;
 222             int shift;
 223             uint32_t period_frac = s->period_frac;
 224             uint64_t period = s->period;
 225
 226             if (!oneshot && (s->delta * period < 10000) &&
 227                 !icount_enabled() && !qtest_enabled()) {
 228                 period = 10000 / s->delta;
 229                 period_frac = 0;
 230             }
 231
 232             /* We need to divide time by period, where time is stored in
 233                rem (64-bit integer) and period is stored in period/period_frac
 234                (64.32 fixed point).
 235
 236                Doing full precision division is hard, so scale values and
 237                do a 64-bit division.  The result should be rounded down,
 238                so that the rounding error never causes the timer to go
 239                backwards.
 240             */
 241
 242             rem = next - now;
 243             div = period;
 244
 245             clz1 = clz64(rem);
 246             clz2 = clz64(div);
 247             shift = clz1 < clz2 ? clz1 : clz2;
 248
 249             rem <<= shift;
 250             div <<= shift;
 251             if (shift >= 32) {
 252                 div |= ((uint64_t)period_frac << (shift - 32));
 253             } else {
 254                 if (shift != 0)
 255                     div |= (period_frac >> (32 - shift));
 256                 /* Look at remaining bits of period_frac and round div up if
 257                    necessary.  */
 258                 if ((uint32_t)(period_frac << shift))
 259                     div += 1;
 260             }
 261             counter = rem / div;
 262
 263             if (s->policy_mask & PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD) {
 264                 /* Before wrapping around, timer should stay with counter = 0
 265                    for a one period.  */
 266                 if (!oneshot && s->delta == s->limit) {
 267                     if (now == last) {
 268                         /* Counter == delta here, check whether it was
 269                            adjusted and if it was, then right now it is
 270                            that "one period".  */
 271                         if (counter == s->limit + DELTA_ADJUST) {
 272                             return 0;
 273                         }
 274                     } else if (counter == s->limit) {
 275                         /* Since the counter is rounded down and now != last,
 276                            the counter == limit means that delta was adjusted
 277                            by +1 and right now it is that adjusted period.  */
 278                         return 0;
 279                     }
 280                 }
 281             }
 282         }
 283
 284         if (s->policy_mask & PTIMER_POLICY_NO_COUNTER_ROUND_DOWN) {
 285             /* If now == last then delta == limit, i.e. the counter already
 286                represents the correct value. It would be rounded down a 1ns
 287                later.  */
 288             if (now != last) {
 289                 counter += 1;
 290             }
 291         }
 292     } else {
 293         counter = s->delta;
 294     }
 295     return counter;
 296 }
 297
 298 void ptimer_set_count(ptimer_state *s, uint64_t count)
 299 {
 300     assert(s->in_transaction);
 301     s->delta = count;
 302     if (s->enabled) {
 303         s->need_reload = true;
 304     }
 305 }
 306
 307 void ptimer_run(ptimer_state *s, int oneshot)
 308 {
 309     bool was_disabled = !s->enabled;
 310
 311     assert(s->in_transaction);
 312
 313     if (was_disabled && s->period == 0) {
 314         if (!qtest_enabled()) {
 315             fprintf(stderr, "Timer with period zero, disabling\n");
 316         }
 317         return;
 318     }
 319     s->enabled = oneshot ? 2 : 1;
 320     if (was_disabled) {
 321         s->need_reload = true;
 322     }
 323 }
 324
 325 /* Pause a timer.  Note that this may cause it to "lose" time, even if it
 326    is immediately restarted.  */
 327 void ptimer_stop(ptimer_state *s)
 328 {
 329     assert(s->in_transaction);
 330
 331     if (!s->enabled)
 332         return;
 333
 334     s->delta = ptimer_get_count(s);
 335     timer_del(s->timer);
 336     s->enabled = 0;
 337     s->need_reload = false;
 338 }
 339
 340 /* Set counter increment interval in nanoseconds.  */
 341 void ptimer_set_period(ptimer_state *s, int64_t period)
 342 {
 343     assert(s->in_transaction);
 344     s->delta = ptimer_get_count(s);
 345     s->period = period;
 346     s->period_frac = 0;
 347     if (s->enabled) {
 348         s->need_reload = true;
 349     }
 350 }
 351
 352 /* Set counter increment interval from a Clock */
 353 void ptimer_set_period_from_clock(ptimer_state *s, const Clock *clk,
 354                                   unsigned int divisor)
 355 {
 356     /*
 357      * The raw clock period is a 64-bit value in units of 2^-32 ns;
 358      * put another way it's a 32.32 fixed-point ns value. Our internal
 359      * representation of the period is 64.32 fixed point ns, so
 360      * the conversion is simple.
 361      */
 362     uint64_t raw_period = clock_get(clk);
 363     uint64_t period_frac;
 364
 365     assert(s->in_transaction);
 366     s->delta = ptimer_get_count(s);
 367     s->period = extract64(raw_period, 32, 32);
 368     period_frac = extract64(raw_period, 0, 32);
 369     /*
 370      * divisor specifies a possible frequency divisor between the
 371      * clock and the timer, so it is a multiplier on the period.
 372      * We do the multiply after splitting the raw period out into
 373      * period and frac to avoid having to do a 32*64->96 multiply.
 374      */
 375     s->period *= divisor;
 376     period_frac *= divisor;
 377     s->period += extract64(period_frac, 32, 32);
 378     s->period_frac = (uint32_t)period_frac;
 379
 380     if (s->enabled) {
 381         s->need_reload = true;
 382     }
 383 }
 384
 385 /* Set counter frequency in Hz.  */
 386 void ptimer_set_freq(ptimer_state *s, uint32_t freq)
 387 {
 388     assert(s->in_transaction);
 389     s->delta = ptimer_get_count(s);
 390     s->period = 1000000000ll / freq;
 391     s->period_frac = (1000000000ll << 32) / freq;
 392     if (s->enabled) {
 393         s->need_reload = true;
 394     }
 395 }
 396
 397 /* Set the initial countdown value.  If reload is nonzero then also set
 398    count = limit.  */
 399 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload)
 400 {
 401     assert(s->in_transaction);
 402     s->limit = limit;
 403     if (reload)
 404         s->delta = limit;
 405     if (s->enabled && reload) {
 406         s->need_reload = true;
 407     }
 408 }
 409
 410 uint64_t ptimer_get_limit(ptimer_state *s)
 411 {
 412     return s->limit;
 413 }
 414
 415 void ptimer_transaction_begin(ptimer_state *s)
 416 {
 417     assert(!s->in_transaction);
 418     s->in_transaction = true;
 419     s->need_reload = false;
 420 }
 421
 422 void ptimer_transaction_commit(ptimer_state *s)
 423 {
 424     assert(s->in_transaction);
 425     /*
 426      * We must loop here because ptimer_reload() can call the callback
 427      * function, which might then update ptimer state in a way that
 428      * means we need to do another reload and possibly another callback.
 429      * A disabled timer never needs reloading (and if we don't check
 430      * this then we loop forever if ptimer_reload() disables the timer).
 431      */
 432     while (s->need_reload && s->enabled) {
 433         s->need_reload = false;
 434         s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 435         ptimer_reload(s, 0);
 436     }
 437     /* Now we've finished reload we can leave the transaction block. */
 438     s->in_transaction = false;
 439 }
 440
 441 const VMStateDescription vmstate_ptimer = {
 442     .name = "ptimer",
 443     .version_id = 1,
 444     .minimum_version_id = 1,
 445     .fields = (VMStateField[]) {
 446         VMSTATE_UINT8(enabled, ptimer_state),
 447         VMSTATE_UINT64(limit, ptimer_state),
 448         VMSTATE_UINT64(delta, ptimer_state),
 449         VMSTATE_UINT32(period_frac, ptimer_state),
 450         VMSTATE_INT64(period, ptimer_state),
 451         VMSTATE_INT64(last_event, ptimer_state),
 452         VMSTATE_INT64(next_event, ptimer_state),
 453         VMSTATE_TIMER_PTR(timer, ptimer_state),
 454         VMSTATE_END_OF_LIST()
 455     }
 456 };
 457
 458 ptimer_state *ptimer_init(ptimer_cb callback, void *callback_opaque,
 459                           uint8_t policy_mask)
 460 {
 461     ptimer_state *s;
 462
 463     /* The callback function is mandatory. */
 464     assert(callback);
 465
 466     s = g_new0(ptimer_state, 1);
 467     s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, ptimer_tick, s);
 468     s->policy_mask = policy_mask;
 469     s->callback = callback;
 470     s->callback_opaque = callback_opaque;
 471
 472     /*
 473      * These two policies are incompatible -- trigger-on-decrement implies
 474      * a timer trigger when the count becomes 0, but no-immediate-trigger
 475      * implies a trigger when the count stops being 0.
 476      */
 477     assert(!((policy_mask & PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT) &&
 478              (policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)));
 479     return s;
 480 }
 481
 482 void ptimer_free(ptimer_state *s)
 483 {
 484     timer_free(s->timer);
 485     g_free(s);
 486 }