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arcv2_timer: fix cycle count race

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It's possible the timer interrupt could occur when performing the
computation, resulting in incorrect values returned.

It's still possible for bad values to be returned if the function is
called with interrupts locked, but that is only fixable with a second
timer source.

Issue: ZEP-1546
Change-Id: I16d5b04c3e32377f7249eb4fb1bf2f7c22bd0836
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
This commit is contained in:
Andrew Boie 2017-02-15 16:00:43 -08:00
commit 15b8ed1a6a
1 changed files with 9 additions and 2 deletions
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11
drivers/timer/arcv2_timer0.c
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@ -66,7 +66,7 @@
/* running total of timer count */ /* running total of timer count */
static uint32_t __noinit cycles_per_tick; static uint32_t __noinit cycles_per_tick;
static uint32_t accumulated_cycle_count; static volatile uint32_t accumulated_cycle_count;
#ifdef CONFIG_TICKLESS_IDLE #ifdef CONFIG_TICKLESS_IDLE
static uint32_t __noinit max_system_ticks; static uint32_t __noinit max_system_ticks;
@ -415,7 +415,14 @@ int sys_clock_device_ctrl(struct device *port, uint32_t ctrl_command,
uint32_t _timer_cycle_get_32(void) uint32_t _timer_cycle_get_32(void)
{ {
return (accumulated_cycle_count + timer0_count_register_get()); uint32_t acc, count;
do {
acc = accumulated_cycle_count;
count = timer0_count_register_get();
} while (acc != accumulated_cycle_count);
return acc + count;
} }
#if defined(CONFIG_SYSTEM_CLOCK_DISABLE) #if defined(CONFIG_SYSTEM_CLOCK_DISABLE)