drivers: rtc: stm32: allow new RTC driver to work with BBRAM

STM32 BBRAM depends on RTC to work. This changes STM32 RTC init stage to
PRE_KERNEL_1 to allow RTC driver to initialize before BBRAM driver.

Some adjustments are made so that kernel API is not used during the init
procedure.

Signed-off-by: Johan Lafon <johan.lafon@syslinbit.com>

drivers/bbram/Kconfig.stm32

@@ -5,7 +5,7 @@ config BBRAM_STM32
 	bool "ST STM32 Battery-backed RAM drivers"
 	default y
 	depends on DT_HAS_ST_STM32_BBRAM_ENABLED
-	depends on COUNTER
+	depends on COUNTER_RTC_STM32 || RTC_STM32
 	help
 	  This option enables the BBRAM driver for STM32 family of
 	  processors.

drivers/rtc/Kconfig.stm32

@@ -5,6 +5,7 @@ config RTC_STM32
 	bool "STM32 RTC driver"
 	default y if !COUNTER
 	depends on DT_HAS_ST_STM32_RTC_ENABLED && !SOC_SERIES_STM32F1X
+	select USE_STM32_LL_RTC
 	select USE_STM32_LL_PWR
 	select USE_STM32_LL_RCC
 	help

drivers/rtc/rtc_ll_stm32.c

@@ -25,6 +25,8 @@
 
 #include <zephyr/logging/log.h>
 
+#include <stdbool.h>
+
 LOG_MODULE_REGISTER(rtc_stm32, CONFIG_RTC_LOG_LEVEL);
 
 /* RTC start time: 1st, Jan, 2000 */
@@ -68,15 +70,25 @@ struct rtc_stm32_data {
 	struct k_mutex lock;
 };
 
-static int rtc_stm32_enter_initialization_mode(void)
+static int rtc_stm32_enter_initialization_mode(bool kernel_available)
 {
+	if (kernel_available) {
 		LL_RTC_EnableInitMode(RTC);
-
 		bool success = WAIT_FOR(LL_RTC_IsActiveFlag_INIT(RTC), RTC_TIMEOUT, k_msleep(1));
 
 		if (!success) {
 			return -EIO;
 		}
+	} else {
+		/* kernel is not available so use the blocking but otherwise equivalent function
+		 * provided by LL
+		 */
+		ErrorStatus status = LL_RTC_EnterInitMode(RTC);
+
+		if (status != SUCCESS) {
+			return -EIO;
+		}
+	}
 
 	return 0;
 }
@@ -104,7 +116,7 @@ static int rtc_stm32_configure(const struct device *dev)
 	if ((hour_format != LL_RTC_HOURFORMAT_24HOUR) ||
 	    (sync_prescaler != cfg->sync_prescaler) ||
 	    (async_prescaler != cfg->async_prescaler)) {
-		err = rtc_stm32_enter_initialization_mode();
+		err = rtc_stm32_enter_initialization_mode(false);
 		if (err == 0) {
 			LL_RTC_SetHourFormat(RTC, LL_RTC_HOURFORMAT_24HOUR);
 			LL_RTC_SetSynchPrescaler(RTC, cfg->sync_prescaler);
@@ -191,7 +203,7 @@ static int rtc_stm32_set_time(const struct device *dev, const struct rtc_time *t
 	LOG_INF("Setting clock");
 	LL_RTC_DisableWriteProtection(RTC);
 
-	err = rtc_stm32_enter_initialization_mode();
+	err = rtc_stm32_enter_initialization_mode(true);
 	if (err) {
 		k_mutex_unlock(&data->lock);
 		return err;
@@ -387,5 +399,5 @@ static const struct rtc_stm32_config rtc_config = {
 
 static struct rtc_stm32_data rtc_data;
 
-DEVICE_DT_INST_DEFINE(0, &rtc_stm32_init, NULL, &rtc_data, &rtc_config, POST_KERNEL,
+DEVICE_DT_INST_DEFINE(0, &rtc_stm32_init, NULL, &rtc_data, &rtc_config, PRE_KERNEL_1,
 		      CONFIG_RTC_INIT_PRIORITY, &rtc_stm32_driver_api);