On Tue, Oct 20, 2015 at 8:20 PM, Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> 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. This problem is now moving into u-boot which is using DT for configuration. > 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.) I'm missing context of what you did, but it needs to be parse-able from a flattened tree. My suggestion would be use clock-frequency property in the uart node. We should be able to parse that. This came up with u-boot as well[1]. > In order to be independent of a boot loader, we also need > [3] pinctrl (pin-muxing) We have to draw the line somewhere and I think this falls below it. What if we have to turn on a regulator for the pins or RS-232 transceiver, turn on power domain, take peripheral out of reset, and the list goes on... Hopefully a debug path would never be that complicated. > But, it is difficult to handle pinctrl in the earlycon framework. earlycon is for debug. Either fix your bootloader or you need some platform specific setup hacks to get the h/w in a working state if you need to debug. Rob [1] https://patchwork.ozlabs.org/patch/492697/ -- 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
