Re: [Qemu-devel] Can not hotplug device to pci-to-pci bridge using machine type older than 1.7

[Fei Li]

On 01/29/2018 09:33 PM, Igor Mammedov wrote:
> On Thu, 25 Jan 2018 16:01:39 +0800
> Fei Li <address@hidden> wrote:
>
> > Hi,
> >
> > After I hotplug a pci device to a pci2pci bridge (I use "pci.1") with
> > machine type 1.7 or older,
> > I can not see the pci device via `lspci` in the guest, but can see it
> > via `info qtree` in the hmp.
> > What's more, after I reboot the guest or hotplug another pci device to
> > pci.0, I can see the
> > previous hotplugged pci device via `lspci`.
> >
> > I use qemu v2.9.* (but machine type =1.7 or 1.6) and kernel 4.4.
> > I also do the test on self-build qemu v1.7, v1.6 and kernel 4.4, the
> > same phenomenon.
> > My qemu command line is as follows:
> > /usr/bin/qemu-system-x86_64 -m 1024 -machine
> > pc-i440fx-1.7,accel=kvm,kernel_irqchip=on -enable-kvm \
> > -smp sockets=1,cores=1,threads=1 -no-user-config -cpu Skylake-Client \
> > -name "pci-hp-qemu" -monitor telnet:127.0.0.1:8848,server,nowait \
> > -drive file=/opt/pcihp.qcow2,if=none,id=drive0,format=qcow2 \
> > -device virtio-blk-pci,drive=drive0,id=sata0,bootindex=1 \
> > -device pci-bridge,chassis_nr=1 \
> > -device virtio-net-pci,bus=pci.1,addr=01,id=netdev1 \
> > -device virtio-net-pci,bus=pci.0,addr=07,id=netdev2 \
> > -boot order=c
> > ...
> > (qemu) device_add virtio-net-pci,bus=pci.1,addr=12,id=netdev12
> >
> > Checking the qemu commit log, I see qemu v2.0 introduces the acpi based
> > pci hotplug
> > support and enables hotplug for pci devices behind pci2pci bridges
> > (upstream commit 99fd437d, 9e047b98 and db4728e6).
> >
> > I also checked qemu v2.9 code, and notice there's a judge: if
> > use_acpi_pci_hotplug is true (MT >= 2.0),
> > the code will update the hotplug_handler for *all buses* to PIIX4PMState
> > and uses
> > acpi_pcihp_device_plug_cb as the hp callback; else, for MT<=1.7, the
> > code will only update the
> > hotplug_handler for pci.0 and leave other buses continue to use its
> > default hp_handler: the
> > pci2pci bridge and default callback: pci_bridge_dev_hotplug_cb =>
> > shpc_device_hotplug_cb.
> > With the latter shpc* hotplug callback, hotplug a pci device to a
> > pci2pci bridge, like pci.1, I can
> > not be seen it in the guest via `lspci`.
> >
> > I am just wondering whether the qemu code does not support the shpc
> > hotplug to pci2pci bridge,
> Last time, it used to 'work' i.e. guest is notified but fails to init
> hotplugged device due to lack of IO resources.
>
> I'd suggest to start looking at issue from guest side and see what
> SHPC driver does to figure out if something in QEMU/firmware needs
> to be fixed.
Sorry for my late reply..
Thanks very much for giving me the clear direction. I am afraid I need more
time to locate the reason. Considering pcihp to pci2pci bridge with old MT
(<=1.7) is a rare scenario, I'd like to continue investigating as long 
as I have
enough free time. :)

Again, thanks for your kindly suggestions.
Fei

> > or the shpc spec does not support this.
> > Could someone shed some light on me? Thanks a lot!
> >
> > Have a nice day
> > Fei