From mboxrd@z Thu Jan  1 00:00:00 1970
From: Cornelia Huck <cornelia.huck@de.ibm.com>
Subject: Re: [PATCH 5/5] KVM: s390: Split out early console code.
Date: Tue, 30 Oct 2012 15:29:49 +0100
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To: Alexander Graf <agraf@suse.de>
Cc: Avi Kivity <avi@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, KVM <kvm@vger.kernel.org>, linux-s390 <linux-s390@vger.kernel.org>, Christian Borntraeger <borntraeger@de.ibm.com>, Carsten Otte <cotte@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Sebastian Ott <sebott@linux.vnet.ibm.com>
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On Tue, 30 Oct 2012 14:43:10 +0100
Alexander Graf <agraf@suse.de> wrote:

> On 10/30/2012 01:59 PM, Cornelia Huck wrote:
> > On Mon, 29 Oct 2012 19:14:19 +0100
> > Alexander Graf<agraf@suse.de>  wrote:
> >
> >> On 29.10.2012, at 14:07, Cornelia Huck wrote:
> >>
> >>> This code is transport agnostic and can be used by both the legacy
> >>> virtio code and virtio_ccw.
> >> Would it be possible to actually send real virtio or sclp console commands for early printk? That'd make things a lot easier on the user space end. Combining two completely separate character channels (early printk + sclp or early printk + virtio-console) is really tricky.
> >>
> > This code is only used if we use a virtio console device. The sclp
> > code path is completely different.
> 
> Ah, so the sclp early console works differently?

sclp consoles are registered via console_initcall(). I'm not aware of
'early' handling there (although I don't really know the code well.)

> 
> > What do you mean with "real virtio console commands"? The message is
> > just put on the output queue anyway.
> 
> For virtio-console, yes. For the early printk it is sent to the 
> hypervisor using a hypercall, not through the virtio queue. So it 
> arrives at a completely different end point that usually has no 
> knowledge of the virtio-console output driver.

virtio setup is a core_initcall, which is done way later than the
console_initcalls (including s390_virtio_console_init). According to
the comments, virtio_cons_early_init is there exactly for that reason.