BACKPORT of upstream NuttX stm32_serial: fix freezing serial port.

   Thanks to Jussi Kivilinna

   https://bitbucket.org/nuttx/nuttx/commits/9169ff6a15fe65ba4af134b470dbf89220274c19

   stm32_serial: fix freezing serial port.  Serial interrupt enable/disable functions
   do not disable interrupts and can freeze device when serial interrupt is received
   while execution is at those functions.

   Trivially triggered with two or more threads write to regular syslog stream and to
   emergency stream. In this case, freeze happens because of mismatch of priv->ie
   (TXEIE == 0) and actually enabled interrupts in USART registers (TXEIE == 1),
   which leads to unhandled TXE interrupt and causes interrupt storm for USART.

nuttx-patches/00026-BACKPORT-stm32fX-serial-fix-freezing.patch

+diff --git NuttX/nuttx/arch/arm/src/stm32/stm32_serial.c NuttX/nuttx/arch/arm/src/stm32/stm32_serial.c
+index 644c810..b885440 100644
+--- NuttX/nuttx/arch/arm/src/stm32/stm32_serial.c
++++ NuttX/nuttx/arch/arm/src/stm32/stm32_serial.c
+@@ -1088,10 +1088,10 @@ static inline void up_serialout(struct up_dev_s *priv, int offset, uint32_t valu
+ }
+ 
+ /****************************************************************************
+- * Name: up_restoreusartint
++ * Name: up_setusartint
+  ****************************************************************************/
+ 
+-static void up_restoreusartint(struct up_dev_s *priv, uint16_t ie)
++static inline void up_setusartint(struct up_dev_s *priv, uint16_t ie)
+ {
+   uint32_t cr;
+ 
+@@ -1113,11 +1113,30 @@ static void up_restoreusartint(struct up_dev_s *priv, uint16_t ie)
+ }
+ 
+ /****************************************************************************
++ * Name: up_restoreusartint
++ ****************************************************************************/
++
++static void up_restoreusartint(struct up_dev_s *priv, uint16_t ie)
++{
++  irqstate_t flags;
++
++  flags = enter_critical_section();
++
++  up_setusartint(priv, ie);
++
++  leave_critical_section(flags);
++}
++
++/****************************************************************************
+  * Name: up_disableusartint
+  ****************************************************************************/
+ 
+-static inline void up_disableusartint(struct up_dev_s *priv, uint16_t *ie)
++static void up_disableusartint(struct up_dev_s *priv, uint16_t *ie)
+ {
++  irqstate_t flags;
++
++  flags = enter_critical_section();
++
+   if (ie)
+     {
+       uint32_t cr1;
+@@ -1154,7 +1173,9 @@ static inline void up_disableusartint(struct up_dev_s *priv, uint16_t *ie)
+ 
+   /* Disable all interrupts */
+ 
+-  up_restoreusartint(priv, 0);
++  up_setusartint(priv, 0);
++
++  leave_critical_section(flags);
+ }
+ 
+ /****************************************************************************
+diff --git NuttX/nuttx/arch/arm/src/stm32f7/stm32_serial.c NuttX/nuttx/arch/arm/src/stm32f7/stm32_serial.c
+index 1f5445a..faae72a 100644
+--- NuttX/nuttx/arch/arm/src/stm32f7/stm32_serial.c
++++ NuttX/nuttx/arch/arm/src/stm32f7/stm32_serial.c
+@@ -1070,10 +1070,10 @@ static inline void up_serialout(struct up_dev_s *priv, int offset, uint32_t valu
+ }
+ 
+ /****************************************************************************
+- * Name: up_restoreusartint
++ * Name: up_setusartint
+  ****************************************************************************/
+ 
+-static void up_restoreusartint(struct up_dev_s *priv, uint16_t ie)
++static inline void up_setusartint(struct up_dev_s *priv, uint16_t ie)
+ {
+   uint32_t cr;
+ 
+@@ -1095,11 +1095,30 @@ static void up_restoreusartint(struct up_dev_s *priv, uint16_t ie)
+ }
+ 
+ /****************************************************************************
++ * Name: up_restoreusartint
++ ****************************************************************************/
++
++static void up_restoreusartint(struct up_dev_s *priv, uint16_t ie)
++{
++  irqstate_t flags;
++
++  flags = enter_critical_section();
++
++  up_setusartint(priv, ie);
++
++  leave_critical_section(flags);
++}
++
++/****************************************************************************
+  * Name: up_disableusartint
+  ****************************************************************************/
+ 
+-static inline void up_disableusartint(struct up_dev_s *priv, uint16_t *ie)
++static void up_disableusartint(struct up_dev_s *priv, uint16_t *ie)
+ {
++  irqstate_t flags;
++
++  flags = enter_critical_section();
++
+   if (ie)
+     {
+       uint32_t cr1;
+@@ -1136,7 +1155,9 @@ static inline void up_disableusartint(struct up_dev_s *priv, uint16_t *ie)
+ 
+   /* Disable all interrupts */
+ 
+-  up_restoreusartint(priv, 0);
++  up_setusartint(priv, 0);
++
++  leave_critical_section(flags);
+ }
+ 
+ /****************************************************************************
+@@ -2928,6 +2949,7 @@ int up_putc(int ch)
+ 
+   up_lowputc(ch);
+   up_restoreusartint(priv, ie);
++
+ #endif
+   return ch;
+ }
+diff --git NuttX/nuttx/arch/arm/src/stm32l4/stm32l4_serial.c NuttX/nuttx/arch/arm/src/stm32l4/stm32l4_serial.c
+index dfef76a..8f1fa77 100644
+--- NuttX/nuttx/arch/arm/src/stm32l4/stm32l4_serial.c
++++ NuttX/nuttx/arch/arm/src/stm32l4/stm32l4_serial.c
+@@ -783,11 +783,11 @@ static inline void stm32l4serial_putreg(FAR struct stm32l4_serial_s *priv,
+ }
+ 
+ /****************************************************************************
+- * Name: stm32l4serial_restoreusartint
++ * Name: stm32l4serial_setusartint
+  ****************************************************************************/
+ 
+-static void stm32l4serial_restoreusartint(FAR struct stm32l4_serial_s *priv,
+-                                          uint16_t ie)
++static inline void stm32l4serial_setusartint(FAR struct stm32l4_serial_s *priv,
++                                             uint16_t ie)
+ {
+   uint32_t cr;
+ 
+@@ -809,12 +809,32 @@ static void stm32l4serial_restoreusartint(FAR struct stm32l4_serial_s *priv,
+ }
+ 
+ /****************************************************************************
++ * Name: up_restoreusartint
++ ****************************************************************************/
++
++static void stm32l4serial_restoreusartint(FAR struct stm32l4_serial_s *priv,
++                                          uint16_t ie)
++{
++  irqstate_t flags;
++
++  flags = enter_critical_section();
++
++  stm32l4serial_setusartint(priv, ie);
++
++  leave_critical_section(flags);
++}
++
++/****************************************************************************
+  * Name: stm32l4serial_disableusartint
+  ****************************************************************************/
+ 
+-static inline void stm32l4serial_disableusartint(FAR struct stm32l4_serial_s *priv,
+-                                                 FAR uint16_t *ie)
++static void stm32l4serial_disableusartint(FAR struct stm32l4_serial_s *priv,
++                                          FAR uint16_t *ie)
+ {
++  irqstate_t flags;
++
++  flags = enter_critical_section();
++
+   if (ie)
+     {
+       uint32_t cr1;
+@@ -851,7 +871,9 @@ static inline void stm32l4serial_disableusartint(FAR struct stm32l4_serial_s *pr
+ 
+   /* Disable all interrupts */
+ 
+-  stm32l4serial_restoreusartint(priv, 0);
++  stm32l4serial_setusartint(priv, 0);
++
++  leave_critical_section(flags);
+ }
+ 
+ /****************************************************************************

nuttx-patches/CMakeLists.txt

@@ -57,6 +57,7 @@ set(nuttx_patches
 	00023-BACKPORT-stm32f7-bkp-reference-fix.patch
 	00024-BACKPORT-stm32f7-serial-dma-hotfix.patch
 	00025-BACKPORT-add-set-ex-to-nsh.patch
+	00026-BACKPORT-stm32fX-serial-fix-freezing.patch
 	90000-PENDING-wip-inflight-to-upstream.patch
 	)