sandbox: Add a debug UART

Add support for the debug UART so that sandbox provides build testing for
this feature.

Signed-off-by: Simon Glass <sjg@chromium.org>

configs/sandbox_defconfig

@@ -1,5 +1,6 @@
 CONFIG_SYS_TEXT_BASE=0
 CONFIG_SYS_MALLOC_F_LEN=0x2000
+CONFIG_DEBUG_UART=y
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_NR_DRAM_BANKS=1
 CONFIG_ANDROID_BOOT_IMAGE=y
@@ -173,6 +174,7 @@ CONFIG_REMOTEPROC_SANDBOX=y
 CONFIG_DM_RESET=y
 CONFIG_SANDBOX_RESET=y
 CONFIG_DM_RTC=y
+CONFIG_DEBUG_UART_SANDBOX=y
 CONFIG_SANDBOX_SERIAL=y
 CONFIG_SMEM=y
 CONFIG_SANDBOX_SMEM=y

drivers/serial/Kconfig

@@ -324,6 +324,15 @@ config DEBUG_UART_MXC
 	  will need to provide parameters to make this work. The driver will
 	  be available until the real driver model serial is running.
 
+config DEBUG_UART_SANDBOX
+	bool "sandbox"
+	depends on SANDBOX_SERIAL
+	help
+	  Select this to enable the debug UART using the sandbox driver. This
+	  provides basic serial output from the console without needing to
+	  start up driver model. The driver will be available until the real
+	  driver model serial is running.
+
 config DEBUG_UART_STM32
 	bool "STMicroelectronics STM32"
 	depends on STM32_SERIAL
@@ -354,6 +363,7 @@ endchoice
 config DEBUG_UART_BASE
 	hex "Base address of UART"
 	depends on DEBUG_UART
+	default 0 if DEBUG_UART_SANDBOX
 	help
 	  This is the base address of your UART for memory-mapped UARTs.
 
@@ -363,6 +373,7 @@ config DEBUG_UART_BASE
 config DEBUG_UART_CLOCK
 	int "UART input clock"
 	depends on DEBUG_UART
+	default 0 if DEBUG_UART_SANDBOX
 	help
 	  The UART input clock determines the speed of the internal UART
 	  circuitry. The baud rate is derived from this by dividing the input

drivers/serial/sandbox.c

@@ -143,6 +143,23 @@ static int sandbox_serial_getc(struct udevice *dev)
 	return result;
 }
 
+#ifdef CONFIG_DEBUG_UART_SANDBOX
+
+#include <debug_uart.h>
+
+static inline void _debug_uart_init(void)
+{
+}
+
+static inline void _debug_uart_putc(int ch)
+{
+	os_putc(ch);
+}
+
+DEBUG_UART_FUNCS
+
+#endif /* CONFIG_DEBUG_UART_SANDBOX */
+
 static int sandbox_serial_setconfig(struct udevice *dev, uint serial_config)
 {
 	u8 parity = SERIAL_GET_PARITY(serial_config);