On 10/20/2015 09:20 PM, Masahiro Yamada wrote: > Hi Peter, > (+ Rob Herring, Stefan Agner) > > 2015-10-20 23:00 GMT+09:00 Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>: >> 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. The 8250 earlycon doesn't try to initialize the hardware (other than masking interrupts) if the baud rate is uninitialized (!device->baud in early_serial8250_setup()). Rather than initializing the h/w to a default of 115200 in ingenic_early_console_setup() when device->baud == 0, it should just mask interrupts. That way the bootloader initialization will be preserved when the options are unspecified on the command line, such as: earlycon=jz4740_uart,mmio32,0x43fb0000 Regards, Peter Hurley PS - Apologies for not reviewing the Ingenic 8250 driver at submission time. -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
