Re: [Qemu-devel] [QEMU][RFC PATCH 4/6] xen-pci: Register PCI in Xen

[Avi Kivity <avi@redhat.com>]

On 03/26/2012 01:45 PM, Stefano Stabellini wrote:
> > >
> > >
> > > Now the problem is: there isn't a simple way to specify the BDF where
> > > you want to create the device; pci_create_simple takes a devfn but most
> > > of the higher level functions (pc_vga_init, pci_nic_init_nofail, ...)
> > > don't export the parameter at the moment.
> > > We would need to be able to tell pc_vga_init where to create the card,
> > > so we would have to export the devfn as a parameter.
> > >
> > 
> > You already have total flexibility with the -device foo parameter.  It
> > allows you to create any device, anywhere, with whatever configuration
> > you want.  Use in conjunction with -nodefconfig.
>
> Thanks, -device looks exactly like what we need!
> However I think that the option to suppress the defaults is -nodefaults.

Correct, as I was just informed in another thread.

>
>
> > You may want your own host/pci bridge that lacks the device 0
> > configuration space.
>
> In order not to disrupt the emulated machine in QEMU too much, I was
> thinking to let QEMU create the default device 0 and device 1:
>
> 00:00.0 Host bridge: Intel Corporation 440FX - 82441FX PMC [Natoma] (rev 02)
> 00:01.0 ISA bridge: Intel Corporation 82371SB PIIX3 ISA [Natoma/Triton II]
> 00:01.1 IDE interface: Intel Corporation 82371SB PIIX3 IDE [Natoma/Triton II]
> 00:01.3 Bridge: Intel Corporation 82371AB/EB/MB PIIX4 ACPI (rev 03)
>
> and then have only the first QEMU register itself for IO events in Xen
> related to these devices. That means that only the first QEMU would
> actually receive any events to handle while the other QEMUs would never
> receive any events for these devices.
>
> Then everything else would go through -device: a device is created
> only if the command line option is passed and in that case QEMU
> also registers itself as the handler of this specific device in Xen.
>
> There is supposed to be no overlaps in the configuration, so if two
> QEMUs both register for the same device Xen would return error and QEMU
> would exit.
>
>
> The reason for doing this is that I am not sure that all OSes would be
> able to cope with the ISA bridge being at a location different than
> 00:01.0 or the IDE controller being on a different device from the ISA
> bridge, considering that they are supposed to be two functions of the
> same device (Intel PIIX southbridge).
> So at that point we might as well leave them as they are and try to
> disrupt the basic config at little as possible.

Yes, but won't all qemus have those 00:01.0 devices and try to register
for them?

What about if two BARs (from different devices) are configured for the
same address ranges?

-- 
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