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

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Message-ID: <87sj27xxjr.fsf@rustcorp.com.au>
Date:	Wed, 01 May 2013 11:37:36 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Alexander Graf <agraf@...e.de>,
	Pranavkumar Sawargaonkar <pranavkumar@...aro.org>
Cc:	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-kernel\@lists.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"patches\@linaro.org" <patches@...aro.org>,
	"linux-kernel\@vger.kernel.org List" <linux-kernel@...r.kernel.org>,
	"kvmarm\@lists.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	Peter Maydell <peter.maydell@...aro.org>
Subject: Re: [PATCH 0/2] Early printk support for virtio console devices.

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.

Cheers,
Rusty.
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