Messages in this thread | | | Date | Wed, 21 Oct 2015 10:20:51 +0900 | Subject | Re: [PATCH v2 2/2] serial: earlycon: allow to specify uartclk in earlycon kernel-parameter | From | Masahiro Yamada <> |
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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.
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
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