[PATCH 0/2] Early printk support for virtio console devices.

Anup Patel anup at brainfault.org
Wed May 1 02:53:49 EDT 2013

On Wed, May 1, 2013 at 7:37 AM, Rusty Russell <rusty at rustcorp.com.au> wrote:
> Alexander Graf <agraf at suse.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.
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