Re: [Qemu-devel] [SeaBIOS] [RFC v2 0/3] Support multiple pci domains in pci_device

[Marcel Apfelbaum <marcel.apfelbaum@gmail.com>]

Hi Gerd,

On 08/28/2018 09:07 AM, Gerd Hoffmann wrote:
>    Hi,
>
>> Since we will not use all 256 buses of an extra PCI domain,
>> I think this space will allow us to support more PCI domains.
> Depends on the use case I guess.  If you just need many pcie devices
> this probably doesn't help.  If you want them for numa support then yes,
> more domains with less devices each can be useful then.

We already support multiple NUMA nodes. We want more devices.
Still, having 4x number of devices we previously supported is
a good step forward.

>
>> How will the flow look like ?
>>
>> 1. QEMU passes to SeaBIOS information of how many extra
>>     PCI domains needs, and how many buses per domain.
>>     How it will pass this info? A vendor specific capability,
>>     some PCI registers or modifying extra-pci-roots fw_cfg file?
> Where is the pxb-pcie device?  0000:$somewhere?  Or $domain:00:00.0?

  0000:$somewhere (On PCI domain 0)



>> 2. SeaBIOS assigns the address for each PCI Domain

>>   and
>>      returns the information to QEMU.
>>      How it will do that? Some pxb-pcie registers? Or do we model
>>      the MMCFG like a PCI BAR?
> If we can access pxb-pcie registers before configuring MMCFG then yes,
> we should use pxb-pcie registers for that.

Yes, we can.

Thanks Gerd!
Marcel

>
> cheers,
>    Gerd
>