linux-kernel - Re: [PATCH 0/2] Early printk support for virtio console devices.

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Message-ID: <CAAhSdy14ofVEdrfc2r3PqLFrTA9kvM+oBVWmXNSWBq2xTxMLiQ@mail.gmail.com>
Date:	Wed, 1 May 2013 12:23:49 +0530
From:	Anup Patel <anup@...infault.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Alexander Graf <agraf@...e.de>,
	Pranavkumar Sawargaonkar <pranavkumar@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"linux-kernel@...r.kernel.org List" <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: [PATCH 0/2] Early printk support for virtio console devices.

On Wed, May 1, 2013 at 7:37 AM, Rusty Russell <rusty@...tcorp.com.au> wrote:
> Alexander Graf <agraf@...e.de> writes:
>> There are not device specific registers in
>> virtio-console. Virtio-console lives behind a virtio bus which doesn't
>> know what these registers are.
>
> You're not going to make coherent arguments without reading that actual
> patch we're discussing.  And you're going to just waste everyone else's
> time.
>
>> Even if you shove it into config space,
>
> Which is what the patch does...
>
>> it'd be broken because config access happens without intercepts on
>> some platforms.
>
> But people keep assuming it, which is one reason virtio_ccw switched
> from passive lguest-style config to active.  Only lguest and the old kvm
> virtio use it, and lguest can change.
>
> An emergency output is a reasonable idea, and this is a reasonable
> implementation.  The question is practical: will it be used?  Because we
> don't implement reasonable ideas which aren't going to be used.

We are already using it for Guest bring-up on APM ARM64 board using
KVMTOOL and so far it has been really helpful in debugging KVM ARM64
guest issues.

Also, this is a very useful debugging method for Guest bring-up on
other architectures supported by KVM and other Hypervisors that
support VirtIO.

>
> Cheers,
> Rusty.
> _______________________________________________
> kvmarm mailing list
> kvmarm@...ts.cs.columbia.edu
> https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm

Regards,
Anup
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