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From: Arnd Bergmann <arnd@arndb.de>
To: Chanwoo Choi <cw00.choi@samsung.com>
Cc: Chanwoo Choi <cwchoi00@gmail.com>,
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Subject: Re: [PATCH v4 2/8] arm64: dts: exynos: Add dts files for 64-bit Exynos5433 SoC
Date: Wed, 04 Mar 2015 10:38:06 +0100
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On Wednesday 04 March 2015 15:59:55 Chanwoo Choi wrote:
> On 03/02/2015 06:22 AM, Arnd Bergmann wrote:
> > On Saturday 28 February 2015 09:47:01 Chanwoo Choi wrote:
> >> "earlycon=exynos4210,0x14C20000" is correct bootparam. You can check
> >> it on Documentation/kernel-parameters.txt as following.
> >>
> >>      exynos4210,<addr>
> >>                 Use early console provided by serial driver available
> >>                 on Samsung SoCs, requires selecting proper type and
> >>                 a correct base address of the selected UART port. The
> >>                 serial port must already be setup and configured.
> >>                 Options are not yet supported.
> >>
> >>
> > 
> > But it's crazy to do this when you have a DT. Please fix the existing
> > devicetree files that use this to just list 'earlycon'.
> > 
> > The syntax above only makes sense for classic board files that we
> > do not support for exynos any more.
> 
> Following earlycon patch for exynos soc was merged in Linux 4.0-rc1.
> - commit-id: b94ba0328d3b36ff95f5074c0e9b44f90dc56bb5 (serial: samsung: Add support for early console)
> Almost Exynos SoC use the same UART IP of Exynos4210.
> 
> If you mean that "earlycon=exynos4210" naming will be changed to "earlycon=exynos",
> we have to modify the drivers/tty/serial/samsung.c.

No, what I mean is that you should use just "earlycon" instead of "earlycon=..."
when you have a DTB. You have the OF_EARLYCON_DECLARE() in the driver as
well, so that should just work.

EARLYCON_DECLARE() is really just a hack that allows users to override the
early console from the command line without modifying the stdout-path
property. Don't put that into a dts file.

	Arnd