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Date: Wed, 06 Mar 2013 10:07:31 +0100
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Subject: Re: [Qemu-devel] [PATCH v13 0/8] pv event interface between host
	and guest
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To: Hu Tao <hutao@cn.fujitsu.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Peter Maydell <peter.maydell@linaro.org>, Andrew Jones <drjones@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, Alex Williamson <alex.williamson@redhat.com>, kvm list <kvm@vger.kernel.org>, Gleb Natapov <gleb@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, Jan Kiszka <jan.kiszka@siemens.com>, Juan Quintela <quintela@redhat.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Markus Armbruster <armbru@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, Blue Swirl <blauwirbel@gmail.com>, Orit Wasserman <owasserm@redhat.com>, Alexander Graf <agraf@suse.de>, Sasha Levin <levinsasha928@gmail.com>, Stefan Hajnoczi <stefanha@redhat.com>, Luiz Capitulino <lcapitulino@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Il 06/03/2013 09:56, Hu Tao ha scritto:
>> > 
>> > Something like this should work (in SeaBIOS's src/acpi-dsdt-isa.dsl):
>> > 
>> >     Device(PEVT) {
>> >         Name(_HID, EisaId("QEMU0001"))
>> >         OperationRegion(PEOR, SystemIO, 0x505, 0x01)
>> >         Field(PEOR, ByteAcc, NoLock, Preserve) {
>> >             PEPT,   8,
>> >         }
>> > 
>> >         Method(_STA, 0, NotSerialized) {
>> >             Store(PEPT, Local0)
>> >             If (LEqual(Local0, Zero)) {
>> >                 Return (0x00)
>> >             } Else {
>> >                 Return (0x0F)
>> >             }
>> >         }
> IIUC, here _STA reads from ioport 0x505, if the result is 0, then the
> device is not present. Otherwise, the device is present. But as Gleb
> said, ''the data you read from unassigned port is not guarantied to be
> zero, it may depend on QEMU version''. What should I do to tell if the
> device is present or not correctly?

The firmware is tied to the QEMU version, so you can rely on unassigned
ports returning zero.

Later we can change this to use fw-cfg.

Paolo