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Date: Wed, 6 Mar 2013 04:48:17 -0500 (EST)
From: Paolo Bonzini <pbonzini@redhat.com>
To: Gleb Natapov <gleb@redhat.com>
Cc: Hu Tao <hutao@cn.fujitsu.com>, Peter Maydell <peter.maydell@linaro.org>,
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Subject: Re: [PATCH v13 0/8] pv event interface between host and guest
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> 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 :)

Then Hu will need to patch the _STA method.

Paolo
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