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drivers/timer/cavs_timer: Fix race in k_cycle_get_64()

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In commit 918a574c88 ("clock: add k_cycle_get_64") this driver was
augmented with a count64() method to get a 64 bit cycle output from
the two-32-bit-word device registers.

Unfortunately it appeared to be trying to use a spinlock around the
two (low/high) reads to protect against overflow.  But that doesn't
work: spinlocks protect against other CPU code using the same
spinlock, not against a hardware counter that is incrementing in real
time!

Thankfully there was already a count() routine in place that does a
detect-overflow-and-retry loop to solve this.  Use that.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
This commit is contained in:
Andy Ross 2021-11-14 14:27:30 -08:00 • committed by Christopher Friedt
commit 0b400d86c0
1 changed files with 1 additions and 12 deletions
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13
drivers/timer/cavs_timer.c
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@ -77,17 +77,6 @@ static uint32_t count32(void)
return shim_regs->walclk32_lo;
}
static uint64_t count64(void)
{
k_spinlock_key_t key = k_spin_lock(&lock);
uint64_t ret = shim_regs->walclk32_lo;
ret |= (uint64_t)shim_regs->walclk32_hi << 32;
k_spin_unlock(&lock, key);
return ret;
}
static void compare_isr(const void *arg)
{
ARG_UNUSED(arg);
@ -195,7 +184,7 @@ uint32_t sys_clock_cycle_get_32(void)
uint64_t sys_clock_cycle_get_64(void)
{
return count64();
return count();
}
/* Runs on secondary cores */