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

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Message-ID: <CAAHg+HipCX2ma6brxj9Kgc3ew39b5e30grLwyun9CViif-5wZQ@mail.gmail.com>
Date:	Fri, 19 Apr 2013 14:55:35 +0530
From:	Pranavkumar Sawargaonkar <pranavkumar@...aro.org>
To:	Will Deacon <will.deacon@....com>
Cc:	Marc Zyngier <Marc.Zyngier@....com>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Anup Patel <anup.patel@...aro.org>,
	Patch Tracking <patches@...aro.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"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>
Subject: Re: [RFC] arm64: Early printk support for virtio-mmio console devices.

Hi Will,
On 19 April 2013 14:35, Will Deacon <will.deacon@....com> wrote:
> Hello,
>
> On Thu, Apr 18, 2013 at 09:48:49AM +0100, Pranavkumar Sawargaonkar wrote:
>> Actually i thought adding a config register will be easier to add a
>> code than writing entire emulation as 8250 emulation will require to
>> deal with dealing with more registers and more code.
>
> kvmtool already has an 8250 emulation! All we need to do is hack together
> something which will allow us to instantiate those ioport devices in a more
> flexible manner (namely, inside the MMIO space for ARM). For earlyprintk, I
> suspect we can get away without an interrupt too, which should simplify
> things a bit to start with.
>
> Regardless of the outcome of this discussion, I think getting the 8250
> working on ARM is definitely something worth doing. If I get time, I'll take
> a look.

I am not against using 8250 emulation (as far as it solves printk
issues for kernel booting logs), but my point is why not to add early
read-write support for virtio console, which also can be useful in
emulation less mach-virt environment also ?

Thanks,
Pranav

>
> Will
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