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

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Message-ID: <CAFEAcA_Xhe2ggxUf=Ezrjozf2Y4h4BtCNPyVG=QD8b6kcqrUnQ@mail.gmail.com>
Date:	Fri, 19 Apr 2013 18:40:18 +0100
From:	Peter Maydell <peter.maydell@...aro.org>
To:	Catalin Marinas <catalin.marinas@....com>
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 19 April 2013 18:14, Catalin Marinas <catalin.marinas@....com> wrote:
> On Fri, Apr 19, 2013 at 05:33:18PM +0100, Peter Maydell wrote:
>> The command line lives in the DTB anyway so if you can't look
>> in the DTB you can't get at earlyprintk config either way.
>
> Linux indeed looks in the DT for the command line and that's what's
> triggering the earlyprintk console but at that stage the DT is flat.
> Unflattening the DT happens later (it requires slab allocator). I
> initially thought about extracting the early console device from the DT
> but when it is flat you can't parse the full hierarchy to get its
> address.

So you could add a DT property that specifies the information in a
format that you can get at at the right time. That's annoying
duplication, but at least it's not in the command line (which is
a raw ascii string that QEMU &co shouldn't have to be parsing or
editing). "/console/type" and "/console/address" or something?

-- PMM
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