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

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

On 2014/6/26 7:04, Slutz, Donald Christopher wrote:
> On 06/24/14 22:49, Chen, Tiejun wrote:
>> 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.
>>
>
> I know for Xen that
>
> tools/firmware/hvmloader/acpi/dsdt.asl
>
> also needs to change:
>
>
>               /* Make cirrues VGA S3 suspend/resume work in Windows
> XP/2003 */
>               Device (VGA)
>               {
> -               Name (_ADR, 0x00020000)
> +               // Address of the VGA (device F function 0)
> +               Name (_ADR, 0x000F0000)
>
>
> is what I have for:
>
> -device VGA,vgamem_mb=8,addr=0xF.0x0
>

Do you mean we need to sync devfn with the passed address to work the 
emulated VGA before the real graphic device driver is called?

Thanks
Tiejun

> I am not sure, but think that QEMU without Xen does this acpi
> adjustment at run time.
>
>
> I also change seabios's config to include more VGA support but
> not sure it is needed.
>
>       -Don Slutz
>
>> Thanks
>> Tiejun
>>