Re: [PATCH] hw/pci-host: Allow extended config space access for Designware PCIe host

[Jason Chien]

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 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 <mst@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.chien@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