[PATCH] arm: am33xx: Fix early debug UART initialization

[Felix Brack <fb@ltec.ch>]

The changes from commit 0dba45864b2a ("arm: Init the debug UART")
prevent the early debug UART from being initialized correctly.
By adding a new SoC specific early UART initialization function this
patch provides a generic location to add the required code. This code
has to be SoC and not board specific.
For the am33xx SoCs the fix consist of configuring early clocks.

Signed-off-by: Felix Brack <fb@ltec.ch>
---

 arch/arm/mach-omap2/am33xx/board.c |  7 +++++++
 drivers/serial/Kconfig             | 13 +++++++++++++
 include/debug_uart.h               | 15 +++++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/arch/arm/mach-omap2/am33xx/board.c b/arch/arm/mach-omap2/am33xx/board.c
index c44667668e..a7f0445b93 100644
--- a/arch/arm/mach-omap2/am33xx/board.c
+++ b/arch/arm/mach-omap2/am33xx/board.c
@@ -604,3 +604,10 @@ int arch_cpu_init_dm(void)
 #endif
 	return 0;
 }
+
+#if IS_ENABLED(CONFIG_DEBUG_UART_SOC_INIT)
+void soc_debug_uart_init(void)
+{
+	setup_early_clocks();
+}
+#endif
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 345d1881f5..3da4064d35 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -490,6 +490,19 @@ config DEBUG_UART_SHIFT
 	  value. Use this value to specify the shift to use, where 0=byte
 	  registers, 2=32-bit word registers, etc.
 
+config DEBUG_UART_SOC_INIT
+	bool "Enable SoC-specific debug UART init"
+	depends on DEBUG_UART
+	help
+	  Boards using the same SoC might require some common settings before
+	  the debug UART can be used. The board specific board_debug_uart_init()
+	  is not the right place for such common settings as they would apply
+	  to a specific board only instead of all boards using the same SoC.
+	  When this option is enabled, the SoC specific function
+	  soc_debug_uart_init() will be called when debug_uart_init() is called.
+	  You can put any code here that is needed to set up the UART ready for
+	  use.
+
 config DEBUG_UART_BOARD_INIT
 	bool "Enable board-specific debug UART init"
 	depends on DEBUG_UART
diff --git a/include/debug_uart.h b/include/debug_uart.h
index 714b369e6f..ebc84c44cd 100644
--- a/include/debug_uart.h
+++ b/include/debug_uart.h
@@ -42,6 +42,12 @@
  * - Immediately afterwards, add DEBUG_UART_FUNCS to define the rest of the
  *     functionality (printch(), etc.)
  *
+ * If your SoC needs additional init for the UART to work, enable
+ * CONFIG_DEBUG_UART_SOC_INIT and write a function called
+ * soc_debug_uart_init() to perform that init. When debug_uart_init() is
+ * called, the init will happen automatically. Board specific code does not
+ * go here, see board_debug_uart_init() below.
+ *
  * If your board needs additional init for the UART to work, enable
  * CONFIG_DEBUG_UART_BOARD_INIT and write a function called
  * board_debug_uart_init() to perform that init. When debug_uart_init() is
@@ -61,6 +67,14 @@
  */
 void debug_uart_init(void);
 
+#ifdef CONFIG_DEBUG_UART_SOC_INIT
+void soc_debug_uart_init(void);
+#else
+static inline void soc_debug_uart_init(void)
+{
+}
+#endif
+
 #ifdef CONFIG_DEBUG_UART_BOARD_INIT
 void board_debug_uart_init(void);
 #else
@@ -192,6 +206,7 @@ void printdec(unsigned int value);
 \
 	void debug_uart_init(void) \
 	{ \
+		soc_debug_uart_init(); \
 		board_debug_uart_init(); \
 		_debug_uart_init(); \
 		_DEBUG_UART_ANNOUNCE \
-- 
2.25.1