drivers: ethernet: stm32: Bugfix PTP clock read on second boundary

Current version of STM32 PTP clock reads current PTP time by querying
second and nanosecond registers sequentially. It is possible for second
to roll over between reading second and nanosecond registers, causing
returned time to be off by a second. This bugfix resolves that issue.

Signed-off-by: Alex Sergeev <[email protected]>

Author: Alex Sergeev

drivers/ethernet/eth_stm32_hal.c

@@ -1196,19 +1196,30 @@ static int ptp_clock_stm32_get(const struct device *dev,
 	struct eth_stm32_hal_dev_data *eth_dev_data = ptp_context->eth_dev_data;
 	ETH_HandleTypeDef *heth = &eth_dev_data->heth;
 	int key;
+	uint32_t second_2;
 
 	key = irq_lock();
 
 #if defined(CONFIG_SOC_SERIES_STM32H7X)
 	tm->second = heth->Instance->MACSTSR;
 	tm->nanosecond = heth->Instance->MACSTNR;
+	second_2 = heth->Instance->MACSTSR;
 #else
 	tm->second = heth->Instance->PTPTSHR;
 	tm->nanosecond = heth->Instance->PTPTSLR;
+	second_2 = heth->Instance->PTPTSHR;
 #endif /* CONFIG_SOC_SERIES_STM32H7X */
 
 	irq_unlock(key);
 
+	if (tm->second != second_2 && tm->nanosecond < NSEC_PER_SEC / 2) {
+		/* Second rollover has happened during first measurement: second register
+		 * was read before second boundary and nanosecond register was read after.
+		 * We will use second_2 as a new second value.
+		 */
+		tm->second = second_2;
+	}
+
 	return 0;
 }