> >> Subject: Re: [Question] Why doesn't PCIe hotplug work for Q35 machine? > >> > >> 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. > > > > OK. Does the PCIe specification say that? > > I appreciate very much that you explain more. > > The closest I could find is in "7.3. Configuration Transaction > Rules"/"7.3.1. Device Number": > > With non-ARI Devices, PCI Express components are restricted to > implementing a single Device Number on their primary interface (Upstream > Port) [...] Downstream Ports that do not have ARI Forwarding enabled > must associate only Device 0 with the device attached to the Logical Bus > representing the Link from the Port. Configuration Requests > targeting the Bus Number associated with a Link specifying Device Number > 0 are delivered to the device attached to the Link; Configuration > Requests specifying all other Device Numbers (1-31) > must be terminated by the Switch Downstream Port or the Root Port with > an Unsupported Request Completion Status (equivalent to Master Abort in > PCI). > Thanks a lot, Paolo.
And I found another issue when cold-plugging don't using slot 0, the PCIe device also can't be searched in guest os. So, I have some questions and ideas: 1. Does qemu support ARI Forwarding for PCIe at present? If yes, how to enable it ? 2. If not, we should add some check for PCIe root ports and downstream ports, meanwhile add explaining document. 3. Those check should add in general code level, both hotplug and coldplug. Am I right? Thanks. Best regards, -Gonglei
