Hi Peter, (+ Rob Herring, Stefan Agner) 2015-10-20 23:00 GMT+09:00 Peter Hurley <pe...@hurleysoftware.com>: > On 10/19/2015 11:36 PM, Masahiro Yamada wrote: >> The input clock frequency varies from device to device, but the >> earlycon uses the fixed frequency (BASE_BAUD * 16). It makes >> impossible to set the correct divisor to the register. > > So the bootloader hasn't setup the serial port?
It does. I use U-boot and the serial port is already set up by U-boot. But, earlycon setup functions update hardware registers. See early_serial8250_setup(), ingenic_early_console_setup(), etc. Without port->uartclk set to a valid value, the init code in earlycon setup does not make sense. What I want to clarify is, what should we do in the earlycon setup function? Currently, I see [1] set device->con->write callback [2] initialize UART port registers For [2], we need to know baudrate and input clock frequency. (and the latter is missing, that's why my patch is here.) In order to be independent of a boot loader, we also need [3] pinctrl (pin-muxing) But, it is difficult to handle pinctrl in the earlycon framework. If we depend on a boot loader, [2] is meaningless. [1] is enough. -- Best Regards Masahiro Yamada -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
