linux-kernel - Re: [PATCH v13 0/8] pv event interface between host and guest

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Message-ID: <20130306093852.GK11223@redhat.com>
Date:	Wed, 6 Mar 2013 11:38:53 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Hu Tao <hutao@...fujitsu.com>,
	Peter Maydell <peter.maydell@...aro.org>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	qemu-devel <qemu-devel@...gnu.org>,
	Markus Armbruster <armbru@...hat.com>,
	Blue Swirl <blauwirbel@...il.com>,
	Orit Wasserman <owasserm@...hat.com>,
	kvm list <kvm@...r.kernel.org>,
	Juan Quintela <quintela@...hat.com>,
	Alexander Graf <agraf@...e.de>,
	Andrew Jones <drjones@...hat.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Kevin Wolf <kwolf@...hat.com>,
	Anthony Liguori <aliguori@...ibm.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v13 0/8] pv event interface between host and guest

On Wed, Mar 06, 2013 at 10:07:31AM +0100, Paolo Bonzini wrote:
> 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.
> 
I thought we agreed to do it from the start :)

--
			Gleb.
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