How to enable early printk Early printk can only be enabled if CONFIG_DEBUG=y or in EXPERT mode. You may want to enable it if you are debugging code that executes before the console is initialized. Note that selecting this option will limit Xen to a single UART definition. Attempting to boot Xen image on a different platform *will not work*, so this option should not be enable for Xens that are intended to be portable. Select one of the "Early printk via * UART" in the choice possible for "Early printk" in the "Debugging options" of Kconfig. You will then need to set other options, which depends on the driver selected. CONFIG_EARLY_UART_BASE_ADDRESS is a mandatory argument, it is the base physical address of the UART to use. Other options depends on the driver selected: - 8250 - CONFIG_EARLY_UART_8250_REG_SHIFT is, optionally, the left-shift to apply to the register offsets within the uart. - pl011 - CONFIG_EARLY_UART_PL011_BAUD_RATE is, optionally, a baud rate which should be used to configure the UART at start of day. If CONFIG_EARLY_UART_PL011_BAUD_RATE is set to 0 then the code will not try to initialize the UART, so that bootloader or firmware settings can be used for maximum compatibility. - CONFIG_EARLY_UART_PL011_MMIO32 is, optionally, used to enable 32-bit only accesses to registers. - scif - CONFIG_EARLY_UART_SCIF_VERSION_* is, optionally, the interface version of the UART. Default to version NONE. - For all other uarts there are no additional options. As a convenience it is also possible to select from a list of predefined configurations available in the list of choice for "Early printk" for specific platform. By default early printk is disabled.