linux-kernel - Re: [PATCH v4 2/8] arm64: dts: exynos: Add dts files for 64-bit Exynos5433 SoC

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Date:	Wed, 04 Mar 2015 10:38:06 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Chanwoo Choi <cw00.choi@...sung.com>
Cc:	Chanwoo Choi <cwchoi00@...il.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Mark Rutland <mark.rutland@....com>,
	devicetree <devicetree@...r.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	Marc Zyngier <marc.zyngier@....com>,
	"catalin.marinas@....com" <catalin.marinas@....com>,
	Olof Johansson <olof@...om.net>,
	"will.deacon@....com" <will.deacon@....com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"jh80.chung@...sung.com" <jh80.chung@...sung.com>,
	Seung-Woo Kim <sw0312.kim@...sung.com>,
	Kukjin Kim <kgene@...nel.org>,
	Abhilash Kesavan <a.kesavan@...sung.com>,
	"chanho61.park@...sung.com" <chanho61.park@...sung.com>,
	"inki.dae@...sung.com" <inki.dae@...sung.com>,
	ideal.song@...sung.com
Subject: Re: [PATCH v4 2/8] arm64: dts: exynos: Add dts files for 64-bit Exynos5433 SoC

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
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