Re: [Qemu-devel] [Question] Why doesn't PCIe hotplug work for Q35 machine?

[Marcel Apfelbaum <marcel.a@redhat.com>]

On Sun, 2014-08-17 at 13:00 +0200, Michael S. Tsirkin wrote:
> On Fri, Aug 15, 2014 at 07:33:29AM +0000, Gonglei (Arei) wrote:
> > Hi,
> > 
> > I noticed that the qemu-2.1 release change log says
> > " PCIe: Basic hot-plug/hot-unplug support for Q35 machine."
> > And then I made a testing for the hotplugging function of Q35.
> > But I'm failed, and I got the dmesg log in guest os as below:
> > 
> > [ 159.035250] Pciehp 0000:05:00.0:pcie24: Button pressed on Slot (0 - 4)
> > [ 159.035274] Pciehp 0000:05:00.0:pcie24: Card present on Slot (0 - 4)
> > [ 159.036517] Pciehp 0000:05:00.0:pcie24: PCI slot #0 - 4 - powering on due to button press.
> > [ 159.188049] Pciehp 0000:05:00.0:pcie24: Failed to check link status
> > [ 159.201968] Pciehp 0000:05:00.0:pcie24: Card not present on Slot (0 - 4)
> > [ 159.202529] Pciehp 0000:05:00.0:pcie24: Already disabled on Slot (0 - 4)
> > 
> > Steps of testing:
> > 
> > #1. QEMU version:
> > 
> > 	The lateset master tree source.
> > 
> > #2. Command line:
> > 
> > ./qemu-system-x86_64 -enable-kvm -m 2048 -machine q35 -device ide-drive,bus=ide.2,drive=MacHDD \ 
> >  -drive id=MacHDD,if=none,file=/mnt/sdb/gonglei/image/redhat_q35.img -monitor stdio -vnc :10 -readconfig ../docs/q35-chipset.cfg
> > QEMU 2.0.93 monitor - type 'help' for more information
> > (qemu) device_add virtio-net-pci,id=nic2,bus=pcie-switch-downstream-port-1-1,addr=1.0
> 
> I don't think you can use any slot except slot 0 for pci express.
Indeed, only slot 0 can be used, try the same without specifying the addr property.

> > (qemu) info network
> > hub 0
> >  \ user.0: index=0,type=user,net=10.0.2.0,restrict=off
> >  \ e1000.0: index=0,type=nic,model=e1000,macaddr=52:54:00:12:34:56
> > 
> > #3. Guest OS:
> > 
> > 	Both rhel-server-7.0-x86_64 and SLES-11-SP3-DVD-x86_64-GM.
> > 
> > #4. Content of ../docs/q35-chipset.cfg:
> > 
> > [snip]
> > 
> > ##
> > # Example PCIe switch with two downstream ports
> > #
> > [device "pcie-switch-upstream-port-1"]
> >   driver = "x3130-upstream"
> >   bus = "ich9-pcie-port-4"
> >   addr = "00.0"
> > 
> > [device "pcie-switch-downstream-port-1-1"]
> >   driver = "xio3130-downstream"
> >   multifunction = "on"
> >   bus = "pcie-switch-upstream-port-1"
> >   addr = "00.0"
> >   port = "1"
> >   chassis = "5"
> > 
> > [device "pcie-switch-downstream-port-1-2"]
> >   driver = "xio3130-downstream"
> >   multifunction = "on"
> >   bus = "pcie-switch-upstream-port-1"
> >   addr = "00.1"
> >   port = "1"
> >   chassis = "6"
> > 
> > [device "ich9-ehci-1"]
> >   driver = "ich9-usb-ehci1"
> >   multifunction = "on"
> >   bus = "pcie.0"
> >   addr = "1d.7"
> > 
> > [snip]
> > 
> > BTW, except testing hotplug of downstream ports, I also test the root port
> > with "device_add virtio-net-pci,id=nic2,bus=ich9-pcie-port-1,addr=1.0", but
> > I got the same result.
> 
> Same thing.
Agreed, and also make sure that ich9-pcie-port-1 is a root port's bus and not
an upstream port's bus.

Thanks,
Marcel

> 
> > Am I wrong in some places? Or a QEMU bug?  Thanks for any help.
> > 
> > Best regards,
> > -Gonglei
> > 
> 
> We might want to add a check for this, to produce a
> better error message.
>