Re: [Qemu-devel] Template for developing a Qe mu device with PCIe and MS

From:

Adnan Khaleel

Subject:

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

Date:

Wed, 25 Aug 2010 17:39:50 -0500

Hi Isaku,

I've made some progress in coding the device template but its no where near complete.

I've created some files and am attaching it to this note. Based on what I could gather from the pcie source files I've made a stab at creating a simple model. I've also attached a file for a simple pci device that works under regular Qemu. I would like to duplicate its functionality in your pcie environment for starters.

Could you please take a look at the files I've created and tell me if I've understood your pcie model correctly. Any help will be truly appreciated.

Adnan

The five files I've modified from your git repository are as follows

hw/pci_ids.h                    // Added vendor id defines
hw/pc_q35.c                    // Device instantiation
hw/pcie_msix_template.h // Device header file
hw/pcie_msix_template.c // Device file
Makefile.objs                   // Added pcie_msix_template.o to list of objects being built

Everything should compile without any warnings or errors.

The last file:
sc_link_pci.c
Is the original PCI device that I'm trying to convert into being PCIe and MSI-X and is included merely for reference to help you understand what I'd like to achieve in your environment.

From: Isaku Yamahata [mailto:address@hidden
To: Adnan Khaleel [mailto:address@hidden
Cc: address@hidden
Sent: Wed, 18 Aug 2010 22:19:04 -0500
Subject: Re: [Qemu-devel] Template for developing a Qemu device with PCIe and MSI-X

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="">
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