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.  */
ptimer_trigger(ptimer_state * s)47 static void ptimer_trigger(ptimer_state *s)
48 {
49     s->callback(s->callback_opaque);
50 }
51 
ptimer_reload(ptimer_state * s,int delta_adjust)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 
ptimer_tick(void * opaque)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 
ptimer_get_count(ptimer_state * s)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 
ptimer_set_count(ptimer_state * s,uint64_t count)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 
ptimer_run(ptimer_state * s,int oneshot)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.  */
ptimer_stop(ptimer_state * s)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.  */
ptimer_set_period(ptimer_state * s,int64_t period)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 */
ptimer_set_period_from_clock(ptimer_state * s,const Clock * clk,unsigned int divisor)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.  */
ptimer_set_freq(ptimer_state * s,uint32_t freq)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.  */
ptimer_set_limit(ptimer_state * s,uint64_t limit,int reload)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 
ptimer_get_limit(ptimer_state * s)410 uint64_t ptimer_get_limit(ptimer_state *s)
411 {
412     return s->limit;
413 }
414 
ptimer_transaction_begin(ptimer_state * s)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 
ptimer_transaction_commit(ptimer_state * s)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 
ptimer_init(ptimer_cb callback,void * callback_opaque,uint8_t policy_mask)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 
ptimer_free(ptimer_state * s)482 void ptimer_free(ptimer_state *s)
483 {
484     timer_free(s->timer);
485     g_free(s);
486 }
487