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drivers/cavs_timer: Fix multiword race with timer counter

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The count register is 64 bits, but we're a 32 bit CPU that can only
read four bytes at a time, so a bit of care is needed to prevent
racing against a wraparound of the low word.  Wrap the low read
between two reads of the high word and make sure it didn't change.

Fixes #31599

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
This commit is contained in:
Andy Ross 2021-02-03 15:06:33 -08:00 • committed by Anas Nashif
commit 71fd58ccac
1 changed files with 16 additions and 1 deletions
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17
drivers/timer/cavs_timer.c
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@ -55,7 +55,22 @@ static void set_compare(uint64_t time)
static uint64_t count(void) static uint64_t count(void)
{ {
return shim_regs->walclk; /* The count register is 64 bits, but we're a 32 bit CPU that
* can only read four bytes at a time, so a bit of care is
* needed to prevent racing against a wraparound of the low
* word. Wrap the low read between two reads of the high word
* and make sure it didn't change.
*/
volatile uint32_t *wc = (void *)&shim_regs->walclk;
uint32_t hi0, hi1, lo;
do {
hi0 = wc[1];
lo = wc[0];
hi1 = wc[1];
} while (hi0 != hi1);
return (((uint64_t)hi0) << 32) | lo;
} }
static uint32_t count32(void) static uint32_t count32(void)