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

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Date:	Fri, 26 Apr 2013 14:33:59 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linaro-kernel@...ts.linaro.org
Cc:	Anup Patel <anup.patel@...aro.org>,
	Peter Maydell <peter.maydell@...aro.org>, patches@...aro.org,
	"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
	Alexander Graf <agraf@...e.de>, kvmarm@...ts.cs.columbia.edu,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/2] Early printk support for virtio console devices.

On Friday 26 April 2013 17:36:16 Anup Patel wrote:
> On 26 April 2013 17:03, Peter Maydell <peter.maydell@...aro.org> wrote:
> > On 26 April 2013 12:19, Alexander Graf <agraf@...e.de> wrote:
> >> MMIO registers are handled by a different layer than the virtio
> >> console itself. After the virtio refactoring in QEMU, they will
> >> be completely separate drivers.
> >
> > Good point -- we don't really want to be mixing up the
> > transport and the backend. You can see it in the kvmtool
> > patch, in fact -- it introduces an "if this is virtio-console"
> > special case into the mmio.c file which previously was
> > entirely backend agnostic.
> 
> Well, we can always have virtio device specific config registers
> handle by virtio device backends and generic virtio config register
> handled by transport.
> 
> kvmtool patch is hacky because it does not provide virtio device
> specific config read/write callbacks.

Couldn't kvmtool implement the interface used by smh_printch()
for early output instead?

Or if that's not a fitting inteface, maybe a psci call for writing
a character to the console?

	Arnd
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