From dd7297fb64eb94fe06a89fd9e8656f499cd8cc15 Mon Sep 17 00:00:00 2001
From: Alan Carvalho de Assis <acassis@gmail.com>
Date: Thu, 16 Jun 2016 13:43:09 -0600
Subject: [PATCH] STM32L4: Add logic reset backup domain early in
 initialization

---
 arch/arm/src/stm32l4/stm32l4_rcc.c  | 53 ++++++++++++++++++++++++++++-
 arch/arm/src/stm32l4/stm32l4_rtc.h  | 20 +++++++++++
 arch/arm/src/stm32l4/stm32l4_rtcc.c |  9 +----
 3 files changed, 73 insertions(+), 9 deletions(-)

diff --git a/arch/arm/src/stm32l4/stm32l4_rcc.c b/arch/arm/src/stm32l4/stm32l4_rcc.c
index 0d51d7afd1..202b90176f 100644
--- a/arch/arm/src/stm32l4/stm32l4_rcc.c
+++ b/arch/arm/src/stm32l4/stm32l4_rcc.c
@@ -89,7 +89,58 @@
  ****************************************************************************/
 
 /************************************************************************************
- * Name: stm32l4_clockconfig
+ * Name: rcc_resetbkp
+ *
+ * Description:
+ *   The RTC needs to reset the Backup Domain to change RTCSEL and resetting the
+ *   Backup Domain renders to disabling the LSE as consequence.   In order to avoid
+ *   resetting the Backup Domain when we already configured LSE we will reset the
+ *   Backup Domain early (here).
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value:
+ *   None
+ *
+ ************************************************************************************/
+
+#if defined(CONFIG_STM32_PWR) && defined(CONFIG_RTC)
+static inline rcc_resetbkp(void)
+{
+  bool init_stat;
+
+  /* Check if the RTC is already configured */
+
+  init_stat = rtc_is_inits();
+  if(!init_stat)
+    {
+       /* Enable write access to the backup domain (RTC registers, RTC
+        * backup data registers and backup SRAM).
+        */
+
+      (void)stm32l4_pwr_enablebkp(true);
+
+      /* We might be changing RTCSEL - to ensure such changes work, we must
+       * reset the backup domain (having backed up the RTC_MAGIC token)
+       */
+
+       modifyreg32(STM32L4_RCC_BDCR, 0, RCC_BDCR_BDRST);
+       modifyreg32(STM32L4_RCC_BDCR, RCC_BDCR_BDRST, 0);
+
+       (void)stm32l4_pwr_enablebkp(false);
+    }
+}
+#else
+#  define rcc_resetbkp()
+#endif
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/************************************************************************************
+ * Name: stm32_clockconfig
  *
  * Description:
  *   Called to establish the clock settings based on the values in board.h.  This
diff --git a/arch/arm/src/stm32l4/stm32l4_rtc.h b/arch/arm/src/stm32l4/stm32l4_rtc.h
index b155bef8b0..222f5bc7c0 100644
--- a/arch/arm/src/stm32l4/stm32l4_rtc.h
+++ b/arch/arm/src/stm32l4/stm32l4_rtc.h
@@ -105,6 +105,26 @@ extern "C"
  * Public Functions
  ****************************************************************************/
 
+/************************************************************************************
+ * Name: rtc_is_inits
+ *
+ * Description:
+ *    Returns 'true' if the RTC has been initialized (according to the RTC itself).
+ *    It will be 'false' if the RTC has never been initialized since first time power
+ *    up, and the counters are stopped until it is first initialized.
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value:
+ *   bool -- true if the INITS flag is set in the ISR.
+ *
+ ************************************************************************************/
+#ifdef CONFIG_RTC_DRIVER
+bool rtc_is_inits(void);
+#endif
+
+
 /****************************************************************************
  * Name: stm32l4_rtc_getdatetime_with_subseconds
  *
diff --git a/arch/arm/src/stm32l4/stm32l4_rtcc.c b/arch/arm/src/stm32l4/stm32l4_rtcc.c
index c894fb54d8..830425e1a7 100644
--- a/arch/arm/src/stm32l4/stm32l4_rtcc.c
+++ b/arch/arm/src/stm32l4/stm32l4_rtcc.c
@@ -250,7 +250,7 @@ static void rtc_dumptime(FAR const struct tm *tp, FAR const char *msg)
  *
  ************************************************************************************/
 
-static bool rtc_is_inits(void)
+bool rtc_is_inits(void)
 {
   uint32_t regval;
 
@@ -832,13 +832,6 @@ int up_rtc_initialize(void)
 
       (void)stm32l4_pwr_enablebkp(true);
 
-#if 0
-      /* Do not reset the backup domain; you will lose your clock setup done in *rcc.c */
-
-      modifyreg32(STM32L4_RCC_BDCR, 0, RCC_BDCR_BDRST);
-      modifyreg32(STM32L4_RCC_BDCR, RCC_BDCR_BDRST, 0);
-#endif
-
 #if defined(CONFIG_STM32L4_RTC_HSECLOCK)
       modifyreg32(STM32L4_RCC_BDCR, RCC_BDCR_RTCSEL_MASK, RCC_BDCR_RTCSEL_HSE);
 #elif defined(CONFIG_STM32L4_RTC_LSICLOCK)