Re: [Qemu-devel] [v2][PATCH 4/8] xen, gfx passthrough: reserve 00:02.0 for INTEL IGD

["Chen, Tiejun" <tiejun.chen@intel.com>]

On 2014/5/19 19:22, Gerd Hoffmann wrote:
>   Hi,
>
>> I think '-vga none' just guarantees the qemu vga cards doesn't occupy
>> 00:02.0, but this doesn't mean others use this specific slot since in
>> qemu internal, we always pass -1 to assign a slot automatically to
>> register a PCI device. So in some cases, we can't get this slot as we
>> expect since that is already assigned previously before we need this.
>
> Yes, -vga, -net nic, -drive if=scsi (maybe more) can internally create
> pci devices with auto slot assignment, which will occupy slot 2 indeed.
> Use -device instead to create the devices.
>
>> PCI: slot 2 function 0 not available for xen-pci-passthrough, in use
>> by xen-platform
>
> Ah, the xen platform device.  /me looks.  Ah, pc_xen_hvm_init creates
> this automatically.  Two options here IMHO:
>
>   (1) Just move it somewhere else explicitly.  For example slot 3, or
>       make it a southbridge function (say 00:01.7).
>   (2) Don't create it automatically, instead expect management add it
>       if needed, using -device xen-plaform,addr=...
>

Gerd,

Sorry I return this discussion again.

As we discussed here, we should never use -vga xxx to avoid occupying 
slot 2. Instead, we will just use -device to create that emulated vga 
device as you said like this:

-device VGA,vgamem_mb=8,addr=0x4

But looks this may issue another problem. That is we can't see anything 
until the vga driver is initialized. I means if we pass `-device 
VGA,vgamem_mb=8,addr=0x4', qemu doesn't expose any vga interface to 
BIOS. Right? Or I'm still missing something.

Thanks
Tiejun