drivers: counter: stm32: config rtc prescaler from DT

Handle RTC prescaler options inside RTC counter driver

Signed-off-by: Jake Greaves <jake.greaves@analog.com>

Author: greavesinator85

drivers/counter/counter_ll_stm32_rtc.c

@@ -94,6 +94,9 @@ struct rtc_stm32_config {
 	struct counter_config_info counter_info;
 	LL_RTC_InitTypeDef ll_rtc_config;
 	const struct stm32_pclken *pclken;
+#if DT_INST_CLOCKS_CELL_BY_IDX(0, 1, bus) == STM32_SRC_HSE
+	uint32_t hse_prescaler;
+#endif
 };
 
 struct rtc_stm32_data {
@@ -593,6 +596,11 @@ static int rtc_stm32_init(const struct device *dev)
 	}
 #endif
 
+#if DT_INST_CLOCKS_CELL_BY_IDX(0, 1, bus) == STM32_SRC_HSE
+	/* Must be configured before selecting the RTC clock source */
+	LL_RCC_SetRTC_HSEPrescaler(cfg->hse_prescaler);
+#endif
+
 	if (LL_RTC_Init(RTC, ((LL_RTC_InitTypeDef *)
 			      &cfg->ll_rtc_config)) != SUCCESS) {
 		return -EIO;
@@ -623,28 +631,65 @@ static struct rtc_stm32_data rtc_data;
 
 static const struct stm32_pclken rtc_clk[] = STM32_DT_INST_CLOCKS(0);
 
+#if DT_INST_CLOCKS_CELL_BY_IDX(0, 1, bus) == STM32_SRC_HSE
+#if STM32_HSE_FREQ % MHZ(1) != 0
+#error RTC clock source HSE frequency should be whole MHz
+#elif STM32_HSE_FREQ < MHZ(16) && defined(LL_RCC_RTC_HSE_DIV_16)
+#define RTC_HSE_PRESCALER LL_RCC_RTC_HSE_DIV_16
+#define RTC_HSE_FREQUENCY (STM32_HSE_FREQ / 16)
+#elif STM32_HSE_FREQ < MHZ(32) && defined(LL_RCC_RTC_HSE_DIV_32)
+#define RTC_HSE_PRESCALER LL_RCC_RTC_HSE_DIV_32
+#define RTC_HSE_FREQUENCY (STM32_HSE_FREQ / 32)
+#elif STM32_HSE_FREQ < MHZ(64) && defined(LL_RCC_RTC_HSE_DIV_64)
+#define RTC_HSE_PRESCALER LL_RCC_RTC_HSE_DIV_64
+#define RTC_HSE_FREQUENCY (STM32_HSE_FREQ / 64)
+#else
+#error RTC does not support HSE frequency
+#endif
+#define RTC_HSE_ASYNC_PRESCALER 125
+#define RTC_HSE_SYNC_PRESCALER  (RTC_HSE_FREQUENCY / RTC_HSE_ASYNC_PRESCALER)
+#endif /* DT_INST_CLOCKS_CELL_BY_IDX(0, 1, bus) == STM32_SRC_HSE */
+
 static const struct rtc_stm32_config rtc_config = {
 	.counter_info = {
 		.max_top_value = UINT32_MAX,
 #ifndef CONFIG_COUNTER_RTC_STM32_SUBSECONDS
 		/* freq = 1Hz for not subsec based driver */
 		.freq = RTCCLK_FREQ / ((RTC_ASYNCPRE + 1) * (RTC_SYNCPRE + 1)),
-#else /* !CONFIG_COUNTER_RTC_STM32_SUBSECONDS */
+#else /* CONFIG_COUNTER_RTC_STM32_SUBSECONDS */
 		.freq = RTCCLK_FREQ / (RTC_ASYNCPRE + 1),
-#endif /* CONFIG_COUNTER_RTC_STM32_SUBSECONDS */
+#endif
 		.flags = COUNTER_CONFIG_INFO_COUNT_UP,
 		.channels = 1,
 	},
 	.ll_rtc_config = {
-		.AsynchPrescaler = RTC_ASYNCPRE,
+#if DT_INST_CLOCKS_CELL_BY_IDX(0, 1, bus) == STM32_SRC_LSI ||                                      \
+	DT_INST_CLOCKS_CELL_BY_IDX(0, 1, bus) == STM32_SRC_LSE
+		.AsynchPrescaler = DT_INST_PROP_OR(0, async_prescaler, RTC_ASYNCPRE),
 #if !defined(CONFIG_SOC_SERIES_STM32F1X)
 		.HourFormat = LL_RTC_HOURFORMAT_24HOUR,
-		.SynchPrescaler = RTC_SYNCPRE,
-#else /* CONFIG_SOC_SERIES_STM32F1X */
+		.SynchPrescaler = DT_INST_PROP_OR(0, sync_prescaler, RTC_SYNCPRE),
+#else  /* CONFIG_SOC_SERIES_STM32F1X */
 		.OutPutSource = LL_RTC_CALIB_OUTPUT_NONE,
-#endif /* CONFIG_SOC_SERIES_STM32F1X */
+#endif /* !CONFIG_SOC_SERIES_STM32F1X */
+#elif DT_INST_CLOCKS_CELL_BY_IDX(0, 1, bus) == STM32_SRC_HSE
+		.AsynchPrescaler =
+			DT_INST_PROP_OR(0, async_prescaler, _HSE_ASYNC_PRESCALER - 1),
+#if !defined(CONFIG_SOC_SERIES_STM32F1X)
+		.HourFormat = LL_RTC_HOURFORMAT_24HOUR,
+		.SynchPrescaler =
+			DT_INST_PROP_OR(0, hse_prescaler, RTC_HSE_SYNC_PRESCALER - 1),
+#else  /* CONFIG_SOC_SERIES_STM32F1X */
+		.OutPutSource = LL_RTC_CALIB_OUTPUT_NONE,
+#endif /* !CONFIG_SOC_SERIES_STM32F1X */
+#else
+#error Invalid RTC SRC
+#endif
 	},
 	.pclken = rtc_clk,
+#if DT_INST_CLOCKS_CELL_BY_IDX(0, 1, bus) == STM32_SRC_HSE
+	.hse_prescaler = DT_INST_PROP_OR(0, hse_prescaler, RTC_HSE_PRESCALER),
+#endif
 };
 
 #ifdef CONFIG_PM_DEVICE

dts/bindings/rtc/st,stm32-rtc.yaml

@@ -17,20 +17,23 @@ properties:
   sync-prescaler:
     type: int
     description: |
-      RTC synchronous prescaler value. Optional, defaulting to set values
-      depending on source clock.
+      RTC synchronous prescaler value. Optional, if not set defaulted in code to:
+      - Selected to give 1 Hz tick rate, bsed on source clock frequency and asynchronous
+        prescaler value
 
   async-prescaler:
     type: int
     description: |
-      RTC asynchronous prescaler value. Optional, defaulting to set values
-      depending on source clock.
+      RTC asynchronous prescaler value. Optional, if not set defaulted in code to:
+      - 0x7F if RTC source clock is LSE/LSI
+      - 1 if using counter with CONFIG_COUNTER_RTC_STM32_SUBSECONDS option
+      - 0x7C if RTC source clock is HSE
 
   hse-prescaler:
     type: int
     description: |
-      RTC HSE prescaler value. Optional, defaulting to set values
-      when HSE is selected as the source clock.
+      RTC HSE prescaler value. Applies only when RTC source clock is HSE.
+      Optional, defaulting to the value calculated based on HSE clock frequency.
 
   calib-out-freq:
     type: int