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drivers/timer: Clamp after tick adjustment, not before

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Some early tickless drivers had a common pattern where they would
compute a tick maximum for the request (i.e. the maximum the hardware
counter can handle) but apply it only on the input tick value and not
on the adjusted final value, opening up the overflow condition it was
supposed to have prevented.

Fixes #20939 (Strictly it fixes the specific pattern that was
discovered in that bug.  It's not impossible that other drivers with
alternative implementations have a similar issue, though they look OK
to me via a quick audit).

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
This commit is contained in:
Andy Ross 2019-11-26 11:27:19 -08:00 • committed by Carles Cufí
commit 5f63c9d907
4 changed files with 33 additions and 14 deletions
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13
drivers/timer/hpet.c
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@ -136,10 +136,17 @@ void z_clock_set_timeout(s32_t ticks, bool idle)
ticks = MAX(MIN(ticks - 1, (s32_t)max_ticks), 0);
k_spinlock_key_t key = k_spin_lock(&lock);
u32_t now = MAIN_COUNTER_REG, cyc;
u32_t now = MAIN_COUNTER_REG, cyc, adj;
u32_t max_cyc = max_ticks * cyc_per_tick;
/* Round up to next tick boundary */
cyc = ticks * cyc_per_tick + (now - last_count) + (cyc_per_tick - 1);
/* Round up to next tick boundary. */
cyc = ticks * cyc_per_tick;
adj = (now - last_count) + (cyc_per_tick - 1);
if (cyc <= max_cyc - adj) {
cyc += adj;
} else {
cyc = max_cyc;
}
cyc = (cyc / cyc_per_tick) * cyc_per_tick;
cyc += last_count;