Messages in this thread | | | Date | Fri, 23 Oct 2015 20:15:33 +0900 | Subject | Re: [PATCH v2 2/2] serial: earlycon: allow to specify uartclk in earlycon kernel-parameter | From | Masahiro Yamada <> |
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2015-10-23 0:34 GMT+09:00 Rob Herring <robh@kernel.org>: > On Tue, Oct 20, 2015 at 8:20 PM, Masahiro Yamada > <yamada.masahiro@socionext.com> wrote: >> Hi Peter, >> (+ Rob Herring, Stefan Agner) >> >> 2015-10-20 23:00 GMT+09:00 Peter Hurley <peter@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. > > 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].
Right.
But, I think things have been going wrong since SPL started to parse a device tree.
-- Best Regards Masahiro Yamada
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