drivers: rtc: STM32U5XX rtc scalers

Allow RTC prescalers to be configurable via dts

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

Author: greavesinator85

drivers/rtc/rtc_ll_stm32.c

@@ -1114,12 +1114,12 @@ BUILD_ASSERT(DT_INST_CLOCKS_HAS_IDX(0, 1), "RTC source clock not defined in the
 static const struct rtc_stm32_config rtc_config = {
 #if DT_INST_CLOCKS_CELL_BY_IDX(0, 1, bus) == STM32_SRC_LSI
 	/* prescaler values for LSI @ 32 KHz */
-	.async_prescaler = 0x7F,
-	.sync_prescaler = 0x00F9,
+	.async_prescaler = DT_INST_PROP_OR(0, async_prescaler, 0x7F),
+ 	.sync_prescaler = DT_INST_PROP_OR(0, sync_prescaler, 0x00FF),
 #elif DT_INST_CLOCKS_CELL_BY_IDX(0, 1, bus) == STM32_SRC_LSE
 	/* prescaler values for LSE @ 32768 Hz */
-	.async_prescaler = 0x7F,
-	.sync_prescaler = 0x00FF,
+	.async_prescaler = DT_INST_PROP_OR(0, async_prescaler, 0x7F),
+ 	.sync_prescaler = DT_INST_PROP_OR(0, sync_prescaler, 0x00FF),
 #elif DT_INST_CLOCKS_CELL_BY_IDX(0, 1, bus) == STM32_SRC_HSE
 	/* prescaler values for HSE */
 	.async_prescaler = RTC_HSE_ASYNC_PRESCALER - 1,

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

@@ -14,6 +14,18 @@ properties:
   reg:
     required: true
 
+  sync-prescaler:
+    type: int
+    description: |
+      RTC synchronous prescaler value. Optional, defaulting to set values
+      depending on source clock.
+
+  async-prescaler:
+    type: int
+    description: |
+      RTC asynchronous prescaler value. Optional, defaulting to set values
+      depending on source clock.
+
   calib-out-freq:
     type: int
     description: |