drivers: bbram: stm32-bbram: fix write for devices with TAMP

On devices where the backup memory is part of the TAMP peripheral, the
Backup Domain Protection prevents write to the backup registers. This
fix disables the protection before writing registers and re-enables it
afterwards.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

Author: aurel32

drivers/bbram/bbram_stm32.c

@@ -11,6 +11,7 @@
 #include <zephyr/drivers/bbram.h>
 #include <zephyr/logging/log.h>
 #include <zephyr/sys/util.h>
+#include <stm32_ll_pwr.h>
 #include <stm32_ll_rtc.h>
 LOG_MODULE_REGISTER(bbram, CONFIG_BBRAM_LOG_LEVEL);
 
@@ -65,6 +66,10 @@ static int bbram_stm32_write(const struct device *dev, size_t offset, size_t siz
 		return -EFAULT;
 	}
 
+#if defined(PWR_CR_DBP) || defined(PWR_CR1_DBP) || defined(PWR_DBPCR_DBP) || defined(PWR_DBPR_DBP)
+	LL_PWR_EnableBkUpAccess();
+#endif /* PWR_CR_DBP || PWR_CR1_DBP || PWR_DBPCR_DBP || PWR_DBPR_DBP */
+
 	for (size_t written = 0; written < size; written += to_copy) {
 		reg = STM32_BKP_REG(STM32_BKP_REG_INDEX(offset + written));
 		begin = STM32_BKP_REG_BYTE_INDEX(offset + written);
@@ -73,6 +78,10 @@ static int bbram_stm32_write(const struct device *dev, size_t offset, size_t siz
 		STM32_BKP_REG(STM32_BKP_REG_INDEX(offset + written)) = reg;
 	}
 
+#if defined(PWR_CR_DBP) || defined(PWR_CR1_DBP) || defined(PWR_DBPCR_DBP) || defined(PWR_DBPR_DBP)
+	LL_PWR_DisableBkUpAccess();
+#endif /* PWR_CR_DBP || PWR_CR1_DBP || PWR_DBPCR_DBP || PWR_DBPR_DBP */
+
 	return 0;
 }