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Re: [Qemu-devel] [PATCH] pci: fix requester id to be the one on root bus

From: Alex Williamson
Subject: Re: [Qemu-devel] [PATCH] pci: fix requester id to be the one on root bus
Date: Wed, 11 May 2016 21:22:03 -0600

On Thu, 12 May 2016 10:40:57 +0800
Peter Xu <address@hidden> wrote:

> On Wed, May 11, 2016 at 04:53:54PM +0300, Michael S. Tsirkin wrote:
> > On Wed, May 11, 2016 at 02:40:31PM +0800, Peter Xu wrote:  
> > > When there are devices under PCI bridge (or bridges), PCI requester ID
> > > should be the one that hooked on the root PCI bus, not the PCI device
> > > itself.
> > > 
> > > Signed-off-by: Peter Xu <address@hidden>  
> > 
> > I think this is only correct for pci bridges, and wrong for pci express 
> > bridges.
> > 
> > How exactly do you test this?  
> I was using Radim's test case:
> bin=x86_64-softmmu/qemu-system-x86_64
> $bin -machine q35,iommu=on,intremap=on,kernel-irqchip=split \
>      -smp cpus=2 -m 1024 -enable-kvm \
>      -device i82801b11-bridge,id=pci.1,bus=pcie.0,addr=0x1e \
>      -device pci-bridge,chassis_nr=2,id=pci.2,bus=pci.1,addr=0x0 \
>      -netdev user,id=user.0,hostfwd=tcp::5555-:22 \
>      -device e1000,netdev=user.0,bus=pci.2,addr=0x1 \
>      -drive 
> file=/var/lib/libvirt/images/vm1.qcow2,format=qcow2,if=none,id=drive-virtio-disk0
>  \
>      -device 
> virtio-blk-pci,scsi=off,bus=pci.2,addr=0x3,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
> This does not boot on v6 series, but can boot with the patch
> mentioned.
> Do you know where I can find any document on related topics?

PCI Express to PCI/PCI-X Bridge Specification rev 1.0
2.3 Assignment of Requester ID and Tag by the Bridge

PCIe-to-PCI bridges assign a requester ID composed of the secondary bus
number with devfn = 0.  Although often on real hardware, the root
complex PCI bridge uses the actual bridge requester ID even though
it's actually a PCIe bridge.  Linux assume that if a bridge has a PCIe
capability with type PCIe-to-PCI/X bridge we use the secondary bus
requester ID, if it has a PCIe capability with type PCI/X-to-PCIe, we
use the bridge requester ID.  If it does not have a PCIe capability we
use the bridge ID except for a few quirked devices known to use the
secondary bus ID.  Yay standards!  Thanks,


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