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

On 2014/5/19 19:22, Gerd Hoffmann wrote:

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=...


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.


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