As far as I know, the order issue is caused by nested device realization. In this case, realizing TYPE_DESIGNWARE_PCIE_HOST will also realize TYPE_DESIGNWARE_PCIE_ROOT(see designware_pcie_host_realize()). device_set_realized() is the function that realizing a device must go through, and this function first realizes the device by dc->realize() and then realizes the device's child bus by qbus_realize(). Whether there is any child bus of the device may depend on dc->realize(). The realization flow will be like a recursive call to device_set_realized(). More precisely, the flow in this case is: qdev_realize() --> ... --> FIRST device_set_realized() --> FIRST dc->realize() --> ... --> designware_pcie_host_realize() --> qdev_realize() --> ... --> SECOND device_set_realized() --> SECOND dc->realize() --> ... --> designware_pcie_root_realize() --> ...--> back to the SECOND device_set_realized() --> SECOND qbus_realize() the CHILD bus "dw-pcie" --> ... --> back to the FIRST device_set_realized() --> FIRST qbus_realize() the PARENT bus "pcie".
I also found this patch <https://lists.gnu.org/archive/html/qemu-devel/2021-11/msg02162.html> that solves the same bus issue. Do you have any suggestions on the order of realization? Thanks! On Thu, Aug 10, 2023 at 5:24 AM Michael S. Tsirkin <m...@redhat.com> wrote: > On Wed, Aug 09, 2023 at 10:22:50AM +0000, Jason Chien wrote: > > In pcie_bus_realize(), a root bus is realized as a PCIe bus and a > non-root > > bus is realized as a PCIe bus if its parent bus is a PCIe bus. However, > > the child bus "dw-pcie" is realized before the parent bus "pcie" which is > > the root PCIe bus. Thus, the extended configuration space is not > accessible > > on "dw-pcie". The issue can be resolved by adding the > > PCI_BUS_EXTENDED_CONFIG_SPACE flag to "pcie" before "dw-pcie" is > realized. > > > > Signed-off-by: Jason Chien <jason.ch...@sifive.com> > > I think we should fix the order of initialization rather than > hack around it. > > > --- > > hw/pci-host/designware.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/hw/pci-host/designware.c b/hw/pci-host/designware.c > > index 9e183caa48..388d252ee2 100644 > > --- a/hw/pci-host/designware.c > > +++ b/hw/pci-host/designware.c > > @@ -694,6 +694,7 @@ static void designware_pcie_host_realize(DeviceState > *dev, Error **errp) > > &s->pci.io, > > 0, 4, > > TYPE_PCIE_BUS); > > + pci->bus->flags |= PCI_BUS_EXTENDED_CONFIG_SPACE; > > > > memory_region_init(&s->pci.address_space_root, > > OBJECT(s), > > -- > > 2.17.1 > >
