ARM: debug: stm32: add UART early console support for STM32MP1

Add support of early console for STM32MP1. Default UART instance is UART4,
but other UART instances can be configured by setting physical and virtual
base addresses in menuconfig.
Signed-off-by: Erwan Le Ray <erwan.leray@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/Kconfig.debug

@@ -1235,6 +1235,18 @@ choice
 
 		  If unsure, say N.
 
+	config STM32MP1_DEBUG_UART
+		bool "Use STM32MP1 UART for low-level debug"
+		depends on MACH_STM32MP157
+		select DEBUG_STM32_UART
+		help
+		  Say Y here if you want kernel low-level debugging support
+		  on STM32MP1 based platforms, wich default UART is wired on
+		  UART4, but another UART instance can be selected by modifying
+		  CONFIG_DEBUG_UART_PHYS and CONFIG_DEBUG_UART_VIRT.
+
+		  If unsure, say N.
+
 	config TEGRA_DEBUG_UART_AUTO_ODMDATA
 		bool "Kernel low-level debugging messages via Tegra UART via ODMDATA"
 		depends on ARCH_TEGRA
@@ -1633,6 +1645,7 @@ config DEBUG_UART_PHYS
 	default 0x3e000000 if DEBUG_BCM_KONA_UART
 	default 0x3f201000 if DEBUG_BCM2836
 	default 0x4000e400 if DEBUG_LL_UART_EFM32
+	default 0x40010000 if STM32MP1_DEBUG_UART
 	default 0x40011000 if STM32F4_DEBUG_UART || STM32F7_DEBUG_UART || \
 				STM32H7_DEBUG_UART
 	default 0x40028000 if DEBUG_AT91_SAMV7_USART1
@@ -1795,6 +1808,7 @@ config DEBUG_UART_VIRT
 	default 0xfcfe8600 if DEBUG_BCM63XX_UART
 	default 0xfd000000 if DEBUG_SPEAR3XX || DEBUG_SPEAR13XX
 	default 0xfd883000 if DEBUG_ALPINE_UART0
+	default 0xfe010000 if STM32MP1_DEBUG_UART
 	default 0xfe017000 if DEBUG_MMP_UART2
 	default 0xfe018000 if DEBUG_MMP_UART3
 	default 0xfe100000 if DEBUG_IMX23_UART || DEBUG_IMX28_UART

arch/arm/include/debug/stm32.S

@@ -9,7 +9,8 @@
 #define STM32_USART_TDR_OFF		0x04
 #endif
 
-#if defined(CONFIG_STM32F7_DEBUG_UART) || defined(CONFIG_STM32H7_DEBUG_UART)
+#if defined(CONFIG_STM32F7_DEBUG_UART) || defined(CONFIG_STM32H7_DEBUG_UART) || \
+	defined(CONFIG_STM32MP1_DEBUG_UART)
 #define STM32_USART_SR_OFF		0x1C
 #define STM32_USART_TDR_OFF		0x28
 #endif