Am 15.06.2011 um 18:34 schrieb Avi Kivity <a...@redhat.com>: > On 06/15/2011 11:24 AM, Alexander Graf wrote: >> I'm actually not quite sure what exactly he's describing here. But if it's >> bypassing the bus logic, it's not a normal PCI device :). Sure, there are >> special case devices that also expose a PCI interface. But real PCI cards >> that you plug in onto the PCI bus can't bypass the interrupt logic of the >> bus, as the only interrupt wires they have go to the bus. And since the PCI >> adapters we use in PC machines in Qemu are all non-special, guests can >> possibly choke on this. >> > > There actually is a special device in qemu - acpi power management is > configured as a PCI device, but its interrupt is hard-wired to gsi 9 and is > edge-triggered (so it can't share the irq line). > > I other devices that are special in this regard to also be part of the > chipset, not devices you can plug into arbitrary slots.
Sure, platform devices can do that. Real PCI cards can not. Have you ever seen an e1000 with direct mapped interrupt lines? :) I admit though that we also emulate platform devices that happen to expose themselves on the PCI bus. It's not common though and I wouldn't expect every OS/driver to be happy about it. Alex >