config DM_SERIAL bool "Enable Driver Model for serial drivers" depends on DM help Enable driver model for serial. This replaces drivers/serial/serial.c with the serial uclass, which implements serial_putc() etc. The uclass interface is defined in include/serial.h. config DEBUG_UART bool "Enable an early debug UART for debugging" help The debug UART is intended for use very early in U-Boot to debug problems when an ICE or other debug mechanism is not available. To use it you should: - Make sure your UART supports this interface - Enable CONFIG_DEBUG_UART - Enable the CONFIG for your UART to tell it to provide this interface (e.g. CONFIG_DEBUG_UART_NS16550) - Define the required settings as needed (see below) - Call debug_uart_init() before use - Call debug_uart_putc() to output a character Depending on your platform it may be possible to use this UART before a stack is available. If your UART does not support this interface you can probably add support quite easily. Remember that you cannot use driver model and it is preferred to use no stack. You must not use this UART once driver model is working and the serial drivers are up and running (done in serial_init()). Otherwise the drivers may conflict and you will get strange output. choice prompt "Select which UART will provide the debug UART" depends on DEBUG_UART config DEBUG_UART_NS16550 bool "ns16550" help Select this to enable a debug UART using the ns16550 driver. You will need to provide parameters to make this work. The driver will be available until the real driver model serial is running. endchoice config DEBUG_UART_BASE hex "Base address of UART" depends on DEBUG_UART help This is the base address of your UART for memory-mapped UARTs. A default should be provided by your board, but if not you will need to use the correct value here. config DEBUG_UART_CLOCK int "UART input clock" depends on DEBUG_UART help The UART input clock determines the speed of the internal UART circuitry. The baud rate is derived from this by dividing the input clock down. A default should be provided by your board, but if not you will need to use the correct value here. config UNIPHIER_SERIAL bool "UniPhier on-chip UART support" depends on ARCH_UNIPHIER && DM_SERIAL help Support for the on-chip UARTs on the Panasonic UniPhier platform.