Add emulation of the ICH9 host chipset as an alternative to the current I440FX emulation. This will allow for better support of PCI-E passthrough since ICH9 uses a PCI-E bus whereas the I440FX only supports a PCI bus.
The QEMU support for the PC machine type is fairly poor today. Most platform devices are modelled as ISA devices whereas the ICH9 does not actually have an ISA bus. Below is a diagram of what the I440FX architecture looks like:
The main bus of the I440FX is PCI and the SuperIO chipset contains an integrated IDE controller, USB controller, and PCI-ISA bridge. The SuperIO chipset (the PIIX4) contains many common devices such as the RTC, PIT, PICs, etc. In addition, there's an special bus (X-Bus) for connecting the PC Keyboard controller and I/O APIC since these require special signals.
Despite how we currently model this in QEMU, the only devices that actually exist on the ISA bus are the Serial controller, Parrellel Port controller, and the Floppy controller.
Compare this to the ICH9 diagram from the Intel ICH9 specification:
The ICH9 has an integrated AHCI controller, USB controller, network adapter, audio adapter, PCI-E and PCI bus, and LPC bus for the SuperIO devices. There is no ISA bus.
In order to implement ICH9 support properly in QEMU, we need to teach the PC devices to not assume the existence of an ISA bus and restructure the code accordingly. Here's a brief list of tasks associated with this: