[libvirt] [PATCH 5/5] conf: add pcie-root controller

[Laine Stump]

On 07/23/2013 11:17 AM, Daniel P. Berrange wrote:
> On Tue, Jul 23, 2013 at 10:44:55AM -0400, Laine Stump wrote:
>> This controller is implicit on q35 machinetypes. It provides 31 PCIe
>> (*not* PCI) slots as controller 0.
>>
>> Currently there are no devices that can connect to pcie-root. For a
>> usable q35 system, we still need to add a "dmi-to-pci-bridge" pci
>> controller, which can connect to pcie-root, and provides pci slots.
> Presumably you have another patch which auto-adds a 'dmi-to-pci-bridge'
> device when we see a q35 machine, so that auto-PCI address assignment
> still works ? If we relied on the user to add that device, then legacy
> apps will not work against a QEMU which defaults to q35, since they'll
> be adding PCI devices but not know that they need to add this bridge.
>

Yes, that is in the works, although it may not be finished today. The
idea is that when you try to get a slot for a PCI device and you only
have pcie slots, we would add a dmi-to-pci-bridge (which provides pci
slots that *can't* be hot-plugged) on a pcie slot, then a pci-bridge
(which provides hot-pluggable pci slots) on the dmi-to-pci-bridge. After
that, all devices that required a hot-pluggable pci slot would
automatically be directed to the pci-bridge.

(Thinking more about it, I guess I do need to *always* add them even
when there are no devices, to allow for hot-plugging later (since we
can't hot-plug a dmi-to-pci-bridge or a pci-bridge). Fortunately that
makes it simpler).