linux-kernel - Re: [PATCH 0/8] Generic serial earlycon

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Message-Id: <201403221054.39799.arnd@arndb.de>
Date:	Sat, 22 Mar 2014 10:54:39 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Rob Herring <robherring2@...il.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Catalin Marinas <catalin.marinas@....com>,
	Russell King <linux@....linux.org.uk>,
	Will Deacon <will.deacon@....com>, x86@...nel.org,
	Rob Herring <robh@...nel.org>
Subject: Re: [PATCH 0/8] Generic serial earlycon

On Friday 21 March 2014, Rob Herring wrote:
> From: Rob Herring <robh@...nel.org>
> 
> This started out as an attempt to add arm64's earlyprintk support to ARM
> in order to get an earlier, runtime setup console on multi-platform
> kernels. The first issue was needing the fixmap support which
> conveniently Mark Salter was working on and is mostly in place now. Like
> many things on ARM and arm64 now, it then became where do I put the now
> common, shared code. After digging more into various early console/printk
> support, it turns out the 8250_early.c setup code was the best starting
> point. 
> 
> This is based on Mark Salter's fixmap support currently in linux-next.
> This is tested on arm64 and ARM with pl011 and 8250. The ARM support
> also requires fixmap and fixed mapping support which are not yet in place.
> I have some patches in my tree to support fixmap, but they need some more
> work. Fortunately, once fixmap is in place, it is just a Kconfig option
> to enable earlycon support on ARM. A git tree is available here[1].
> 
> Based on this series, I would like to add support for doing earlycon
> setup using DT.

Hi Rob,

I like this series a lot, great work!

I would consider the DT parsing support essential here, we should not
merge the patches until that is done as well, because I don't want
to see users pass earlycon command line options in DT when they can
use the established "linux,stdout-path" property instead. I would
expect that in almost every case in which we are booting using DT
today, we can just use linux,stdout-path to locate the device that
the boot loader has already set up and start usign it.

	Arnd
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