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Date: Mon, 04 Mar 2013 11:28:05 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v13 0/8] pv event interface between host
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To: Gleb Natapov <gleb@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, kvm list <kvm@vger.kernel.org>, "Michael S. Tsirkin" <mst@redhat.com>, Hu Tao <hutao@cn.fujitsu.com>, qemu-devel <qemu-devel@nongnu.org>, Markus Armbruster <armbru@redhat.com>, Blue Swirl <blauwirbel@gmail.com>, Orit Wasserman <owasserm@redhat.com>, Juan Quintela <quintela@redhat.com>, Alexander Graf <agraf@suse.de>, Jan Kiszka <jan.kiszka@siemens.com>, Andrew Jones <drjones@redhat.com>, Alex Williamson <alex.williamson@redhat.com>, Sasha Levin <levinsasha928@gmail.com>, Stefan Hajnoczi <stefanha@redhat.com>, Luiz Capitulino <lcapitulino@redhat.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, Marcelo Tosatti <mtosatti@redhat.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>

Il 04/03/2013 11:21, Gleb Natapov ha scritto:
>> > Just to clarify it for Hu Tao, the read from a random ioport is how the
>> > ACPI code will detect presence of the device.
>> > 
> Actually no (at least in the long run, for the first version it may be
> OK).

Agreed.

> Since we want to move DSDT generation into QEMU if device will not
> be present QEMU will not generate corresponded Device() in DSDT, or it
> will generate it with _STA() { Return (0x00)} hard coded.

Yes, this would be good.

> Seabios can do
> the same if we will pass it info about device presence via fw_cfg.

True, but I don't like this a lot.  I don't like splitting decisions
between SeaBIOS and the DSDT, you end up touching code all over the
place and writing ASL is simpler than patching---even with all the
machinery that we have.  It is also simpler to move ASL from SeaBIOS to
OVMF and/or viceversa.  I don't recall what was the opposition to a
fw_cfg driver directly in the DSDT, but I think this would be a good
usage for it.

Splitting it between QEMU and DSDT is a bit better, since you have to
touch QEMU anyway to implement the feature.

Anyhow, this does not apply to the next submission of this series.  I
think we can agree to the compromise of using ACPI but still read the
port in _STA.

Paolo