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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Fri, 27 Jul 2018 18:43:41 +1000
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Subject: Re: [Qemu-devel] [PATCH v2 1/2] ppc/pnv: Add model for Power8 PHB3
 PCIe Host bridge
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To: =?ISO-8859-1?Q?C=E9dric?= Le Goater <clg@kaod.org>, David Gibson <david@gibson.dropbear.id.au>
Cc: qemu-ppc@nongnu.org, qemu-devel@nongnu.org, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, Andrea Bolognani <abologna@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>

On Fri, 2018-07-27 at 10:25 +0200, C=C3=A9dric Le Goater wrote:
> Each PHB creates a pci-bridge device and the PCI bus that comes with it=
.=20
> It makes things easier to define PCI devices.=20
>=20
> It is still quite complex ... Here is a sample :
>=20
> qemu-system-ppc64 -m 2G -machine powernv \
>   -cpu POWER8 -smp 2,cores=3D2,threads=3D1 -accel tcg,thread=3Dmulti \
>   -kernel ./zImage.epapr -initrd ./rootfs.cpio.xz -bios ./skiboot.lid \
>   \
>   -device megasas,id=3Dscsi0,bus=3Dpci.0,addr=3D0x1 \
>   -drive file=3D./rhel7-ppc64le.qcow2,if=3Dnone,id=3Ddrive-scsi0-0-0-0,=
format=3Dqcow2,cache=3Dnone \
>   -device scsi-hd,bus=3Dscsi0.0,channel=3D0,scsi-id=3D0,lun=3D0,drive=3D=
drive-scsi0-0-0-0,id=3Dscsi0-0-0-0,bootindex=3D2 \
>   \
>   -device ich9-ahci,id=3Dsata0,bus=3Dpci.1,addr=3D0x1 \
>   -drive file=3D./ubuntu-ppc64le.qcow2,if=3Dnone,id=3Ddrive0,format=3Dq=
cow2,cache=3Dnone \
>   -device ide-hd,bus=3Dsata0.0,unit=3D0,drive=3Ddrive0,id=3Dide,bootind=
ex=3D1 \
>   -device e1000,netdev=3Dnet0,mac=3DC0:FF:EE:00:00:02,bus=3Dpci.1,addr=3D=
0x2 \
>   -netdev bridge,helper=3D/usr/libexec/qemu-bridge-helper,br=3Dvirbr0,i=
d=3Dnet0 \
>   -device nec-usb-xhci,bus=3Dpci.1,addr=3D0x7 \

I don't understand why. That means you can't put emulated (or real)
PCIe device below it ? Why force them down the path of having a bridge
to legacy PCI always ?

My original intent was to have one such bridge in a machine for the
various default PCI devices qemu has that aren't (yet) PCIe (and also
for testing :-) but I never thought we'd throw one onto every PCIe bus.

Ben.