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hw/ptimer: Fix issues caused by the adjusted timer limit value 

Multiple issues here related to the timer with a adjusted .limit value:

1) ptimer_get_count() returns incorrect counter value for the disabled
timer after loading the counter with a small value, because adjusted limit
value is used instead of the original.

For instance:
    1) ptimer_stop(t)
    2) ptimer_set_period(t, 1)
    3) ptimer_set_limit(t, 0, 1)
    4) ptimer_get_count(t) <-- would return 10000 instead of 0

2) ptimer_get_count() might return incorrect value for the timer running
with a adjusted limit value.

For instance:
    1) ptimer_stop(t)
    2) ptimer_set_period(t, 1)
    3) ptimer_set_limit(t, 10, 1)
    4) ptimer_run(t)
    5) ptimer_get_count(t) <-- might return value > 10

3) Neither ptimer_set_period() nor ptimer_set_freq() are adjusting the
limit value, so it is still possible to make timer timeout value
arbitrary small.

For instance:
    1) ptimer_set_period(t, 10000)
    2) ptimer_set_limit(t, 1, 0)
    3) ptimer_set_period(t, 1) <-- bypass limit correction

Fix all of the above issues by adjusting timer period instead of the limit.
Perform the adjustment for periodic timer only. Use the delta value instead
of the limit to make decision whether adjustment is required, as limit could
be altered while timer is running, resulting in incorrect value returned by
ptimer_get_count.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Message-id: cd141f74f5737480ec586b9c7d18cce1d69884e2.1464367869.git.digetx@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Dmitry Osipenko 2016-06-06 16:59:30 +01:00 committed by Peter Maydell
parent 2a0ee672c9
commit e91171e302
1 changed files with 31 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

51
hw/core/ptimer.c
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@ -35,6 +35,9 @@ static void ptimer_trigger(ptimer_state *s)
static void ptimer_reload(ptimer_state *s)
{
uint32_t period_frac = s->period_frac;
uint64_t period = s->period;
if (s->delta == 0) {
ptimer_trigger(s);
s->delta = s->limit;
@ -45,10 +48,24 @@ static void ptimer_reload(ptimer_state *s)
return;
}
/*
* Artificially limit timeout rate to something
* achievable under QEMU. Otherwise, QEMU spends all
* its time generating timer interrupts, and there
* is no forward progress.
* About ten microseconds is the fastest that really works
* on the current generation of host machines.
*/
if (s->enabled == 1 && (s->delta * period < 10000) && !use_icount) {
period = 10000 / s->delta;
period_frac = 0;
}
s->last_event = s->next_event;
s->next_event = s->last_event + s->delta * s->period;
if (s->period_frac) {
s->next_event += ((int64_t)s->period_frac * s->delta) >> 32;
s->next_event = s->last_event + s->delta * period;
if (period_frac) {
s->next_event += ((int64_t)period_frac * s->delta) >> 32;
}
timer_mod(s->timer, s->next_event);
}
@ -83,6 +100,13 @@ uint64_t ptimer_get_count(ptimer_state *s)
uint64_t div;
int clz1, clz2;
int shift;
uint32_t period_frac = s->period_frac;
uint64_t period = s->period;
if ((s->enabled == 1) && !use_icount && (s->delta * period < 10000)) {
period = 10000 / s->delta;
period_frac = 0;
}
/* We need to divide time by period, where time is stored in
rem (64-bit integer) and period is stored in period/period_frac
@ -95,7 +119,7 @@ uint64_t ptimer_get_count(ptimer_state *s)
*/
rem = s->next_event - now;
div = s->period;
div = period;
clz1 = clz64(rem);
clz2 = clz64(div);
@ -104,13 +128,13 @@ uint64_t ptimer_get_count(ptimer_state *s)
rem <<= shift;
div <<= shift;
if (shift >= 32) {
div |= ((uint64_t)s->period_frac << (shift - 32));
div |= ((uint64_t)period_frac << (shift - 32));
} else {
if (shift != 0)
div |= (s->period_frac >> (32 - shift));
div |= (period_frac >> (32 - shift));
/* Look at remaining bits of period_frac and round div up if
necessary. */
if ((uint32_t)(s->period_frac << shift))
if ((uint32_t)(period_frac << shift))
div += 1;
}
counter = rem / div;
@ -182,19 +206,6 @@ void ptimer_set_freq(ptimer_state *s, uint32_t freq)
count = limit. */
void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload)
{
/*
* Artificially limit timeout rate to something
* achievable under QEMU. Otherwise, QEMU spends all
* its time generating timer interrupts, and there
* is no forward progress.
* About ten microseconds is the fastest that really works
* on the current generation of host machines.
*/
if (!use_icount && limit * s->period < 10000 && s->period) {
limit = 10000 / s->period;
}
s->limit = limit;
if (reload)
s->delta = limit;