Re: [Qemu-devel] Template for developing a Qemu device with PCIe and MSI-X

[Isaku Yamahata <yamahata@valinux.co.jp>]

On Wed, Aug 18, 2010 at 02:10:10PM -0500, Adnan Khaleel wrote:
> Hello Qemu developers,
>
> I'm interested in developing a device model that plugs into Qemu that is based
> on a PCIe interface and uses MSI-X. My goal is to ultimately attach a GPU
> simulator to this PCIe interface and use the entire platfom (Qemu + GPU
> simulator) for studying cpu, gpu interactions.
> 
> I'm not terribly familiar with the Qemu device model and I'm looking for some
> assistance, perhaps a starting template for pcie and msi-x that would offer the
> basic functionality that I could then build upon.
> 
> I have looked at the various devices that already modelled that are included
> with Qemu (v0.12.5 at least) and I've noticed several a few pci devices, eg;
> ne2k and cirrus-pci etc, however only one device truly seems to utilize both
> the technologies that I'm interested in and that is the virtio-pci.c
> 
> I'm not sure what virtio-pci does so I'm not sure if that is a suitable
> starting point for me.
> 
> Any help, suggestions etc would be extremely helpful and much appreciated.

Qemu doesn't support pcie at the moment.
Only partial patches have been merged, still more patches have to
be merged for pcie to fully work. The following repo is available.

git clone http://people.valinux.co.jp/~yamahata/qemu/q35/qemu
git clone http://people.valinux.co.jp/~yamahata/qemu/q35/seabios
git clone http://people.valinux.co.jp/~yamahata/qemu/q35/vgabios

Note: patched seabios and vgabios are needed, you have to pass ACPI DSDT
for q35.
example:
qemu-system-x86_64 -M pc_q35 -acpitable load_header,data=roms/seabios/src/q35-acpi-dsdt.aml

This repo is for those who want to try/develop pcie support,
not for upstream merge. So they include patches unsuitable for upstream.
The repo includes pcie port switch emulator which utilize pcie and
MSI(not MSI-X).

The difference between PCI device and PCIe device is configuration
space size.
By setting PCIDeviceInfo::is_express = 1, you'll get 4K configuration
space. Helper functions for pcie are found in qemu/hw/pcie.c
For msi-x, see qemu/hw/msix.c.

Thanks,
-- 
yamahata