linux-kernel - Re: [RFC] arm64: Early printk support for virtio-mmio console devices.

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Message-ID: <20130419162226.GB5383@localhost.cambridge.arm.com>
Date:	Fri, 19 Apr 2013 17:22:26 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Peter Maydell <peter.maydell@...aro.org>
Cc:	Will Deacon <Will.Deacon@....com>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Patch Tracking <patches@...aro.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Pranavkumar Sawargaonkar <pranavkumar@...aro.org>
Subject: Re: [RFC] arm64: Early printk support for virtio-mmio console
 devices.

On Fri, Apr 19, 2013 at 05:14:36PM +0100, Peter Maydell wrote:
> On 19 April 2013 17:12, Catalin Marinas <catalin.marinas@....com> wrote:
> > On Fri, Apr 19, 2013 at 11:05:47AM +0100, Peter Maydell wrote:
> >> Please make the kernel pick the device out of the device tree
> >> blob. The whole point of device tree is that it's how to tell
> >> the kernel where things live -- making kvmtool/QEMU and/or the
> >> user also have to mess with the kernel command line is awkward
> >> and annoying.
> >
> > For a normal console device, it indeed needs to get it from the DT. For
> > early console, you want it earlier than DT parsing so we pass it on the
> > kernel command line via the earlyprintk= parameter.
> 
> You should fix your DT handling code so you can get at the info
> when you need it rather than pushing the problem into bootloaders
> and QEMU, please. DT is your data structure so feel free to
> (re)design it so relevant information can be accessed early
> if that's useful.

earlyprintk is used for debugging early problems, like DT parsing. You
don't have to use it unless you are debugging something. Without
earlyprintk you just get a normal console during boot, based on the DT
description.

-- 
Catalin
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