drivers: counter: stm32: Add support for HSE as RTC clock source

Add Kconfig options COUNTER_RTC_STM32_CLOCK_HSE and
COUNTER_RTC_STM32_HSE_DIV to allow configuring HSE as the RTC clock
source.

Signed-off-by: Markus Fuchs <[email protected]>

Author: mrfuchs

drivers/counter/Kconfig.stm32_rtc

@@ -30,6 +30,14 @@ config COUNTER_RTC_STM32_CLOCK_LSE
 	help
 	  Use LSE as RTC clock
 
+config COUNTER_RTC_STM32_CLOCK_HSE
+	bool "HSE"
+	depends on SOC_SERIES_STM32F2X || SOC_SERIES_STM32F4X || \
+		   SOC_SERIES_STM32F7X || SOC_SERIES_STM32H7X || \
+		   SOC_SERIES_STM32L0X || SOC_SERIES_STM32L1X
+	help
+	  Use HSE as RTC clock. An appropriate prescaler must be set.
+
 endchoice #COUNTER_RTC_STM32_CLOCK_SRC
 
 if !SOC_SERIES_STM32F4X
@@ -75,6 +83,13 @@ config COUNTER_RTC_STM32_LSE_BYPASS
 	help
 	  Enable LSE bypass
 
+config COUNTER_RTC_STM32_HSE_DIV
+	int "HSE prescaler"
+	depends on COUNTER_RTC_STM32_CLOCK_HSE
+	default 0
+	help
+	  HSE division factor for obtaining a 1 MHz RTC clock
+
 config COUNTER_RTC_STM32_BACKUP_DOMAIN_RESET
 	bool "Do backup domain reset"
 	default y

drivers/counter/counter_ll_stm32_rtc.c

@@ -52,6 +52,11 @@ LOG_MODULE_REGISTER(counter_rtc_stm32, CONFIG_COUNTER_LOG_LEVEL);
 #define RTC_EXTI_LINE	LL_EXTI_LINE_17
 #endif
 
+/* Macro to fill up HSE prescaler values */
+#define fn_hse_prescaler(v) LL_RCC_RTC_HSE_DIV_ ## v
+#define hse_prescaler(v) fn_hse_prescaler(v)
+#define LL_RCC_RTC_HSE_DIV_0 LL_RCC_RTC_NOCLOCK
+
 struct rtc_stm32_config {
 	struct counter_config_info counter_info;
 	struct stm32_pclken pclken;
@@ -310,6 +315,16 @@ static int rtc_stm32_init(const struct device *dev)
 
 	LL_RCC_SetRTCClockSource(LL_RCC_RTC_CLKSOURCE_LSI);
 
+#elif defined(CONFIG_COUNTER_RTC_STM32_CLOCK_HSE)
+
+	LL_RCC_SetRTC_HSEPrescaler(hse_prescaler(CONFIG_COUNTER_RTC_STM32_HSE_DIV));
+
+	/* Wait until HSE is ready */
+	while (LL_RCC_HSE_IsReady() != 1) {
+	}
+
+	LL_RCC_SetRTCClockSource(LL_RCC_RTC_CLKSOURCE_HSE);
+
 #else /* CONFIG_COUNTER_RTC_STM32_CLOCK_LSE */
 
 #if !defined(CONFIG_SOC_SERIES_STM32F4X) &&	\
@@ -396,6 +411,10 @@ static const struct rtc_stm32_config rtc_config = {
 		/* prescaler values for LSI @ 32 KHz */
 		.AsynchPrescaler = 0x7F,
 		.SynchPrescaler = 0x00F9,
+#elif defined(CONFIG_COUNTER_RTC_STM32_CLOCK_HSE)
+		/* prescaler values for divided HSE @ 1 MHz */
+		.AsynchPrescaler = 0x7C,
+		.SynchPrescaler = 0x1F3F,
 #else /* CONFIG_COUNTER_RTC_STM32_CLOCK_LSE */
 		/* prescaler values for LSE @ 32768 Hz */
 		.AsynchPrescaler = 0x7F,