Re: [Qemu-devel] [RFC v5 0/6] pci_expander_brdige: support separate pci domain for pxb-pcie

[Marcel Apfelbaum]

 Hi Zihan,

On 09/18/2018 04:41 PM, Michael S. Tsirkin wrote:
> Cc Laine, Eric for an opinion about the management interface.
>
> On Mon, Sep 17, 2018 at 10:57:31PM +0800, Zihan Yang wrote:
> > Hi all
> >
> > Here is a minimal working version of supporting multiple pci domains.
> > The next a few paragraphs will illustrate the purpose and use example.
> > Current issue and limitations will be in last 2 paragraphs, followed
> > by the changelog of each verison.
> >
> > Currently only q35 host bridge is allocated an item in MCFG table, all
> > pxb-pcie host bridges stay within pci domain 0. This series of patches
> > allow each pxb-pcie to be put in separate pci domain, allocating a new
> > MCFG table item for it.
> >
> > Users can configure whether to put pxb host bridge into separate domain
> > by specifying property 'domain_nr' of pxb-pcie device. 'bus_nr' property
> > indicates the Base Bus Number(BBN) of the pxb-pcie host bridge. Another
> > property max_bus specifies the maximum desired bus numbers to reduce
> > MCFG space cost. Example command is
> >
> >      -device pxb-pcie,id=bridge3,bus="pcie.0",domain_nr=1,max_bus=15
> >
> > Then this pxb-pcie host bridge is placed at pci domain 1, and only reserve
> > (15+1)=16 buses, which is much smaller than the default 256 buses.
> >
> > Compared with previous version, this version is much simpler because
> > mcfg of extra domain now has a relatively fixed address, as suggested
> > by Marcel and Gerd. Putting extra mmconfig above 4G and let seabios
> > leave them for guest os will be expected in next version. The range is
> > [0x80000000, 0xb0000000), which allows us to hold 4x busses compared
> > with before.
> >
> > A complete command line for test is follows, you need to replace GUEST_IMAGE,
> > DATA_IMAGE and SEABIOS_BIN with proper environment variable
> >
> > ./x86_64-softmmu/qemu-system-x86_64 \
> >      -machine q35,accel=kvm -smp 2 -m 2048 \
> >      -drive file=${GUEST_IMAGE}  -netdev user,id=realnet0 \
> >      -device e1000e,netdev=realnet0,mac=52:54:00:12:34:56 \
> >      -device pxb-pcie,id=bridge3,bus="pcie.0",domain_nr=1 \
> >      -device pcie-root-port,id=rp1,bus=bridge3,addr=1c.0,port=8,chassis=8 \
> >      -drive if=none,id=drive0,file=${DATA_IMAGE} \
> >      -device virtio-scsi-pci,id=scsi,bus=rp1,addr=00.0 \
> >      -bios ${SEABIOS_BIN}
> >
> > There are a few limitations, though
> > 1. Legacy interrupt routing is not dealt with yet. There is only support for
> >     devices using MSI/MSIX
> That's probably a must have. What makes it hard to add?

Zihan, can you please elaborate on what is the exact problem?
pxb-pcie devices placed in PCI domain 0 do support
legacy  interrupts, the question is what is different for multiple
PCI domains.

Thanks,
Marcel

>

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