Re: [Qemu-devel] [RFC for-2.10 2/3] pci: Allow host bridges to override PCI/PCIe hybrid device behaviour

[Eduardo Habkost]

On Tue, Mar 28, 2017 at 01:16:50PM +1100, David Gibson wrote:
> Currently PCI/PCIe hybrid devices - that is, devices which can appear as
> either plain PCI or PCIe depending on where they're attached - will only
> appear in PCIe mode if they're attached to a PCIe bus via a root port or
> downstream port.
> 
> This is correct for "standard" PCIe setups, but there are some platforms
> which need different behaviour (notably "pseries" whose paravirtualized
> PCI host bridges have some idiosyncracies).
> 
> This patch allows the host bridge to override the normal behaviour.
> 
> Signed-off-by: David Gibson <address@hidden>
> ---
>  hw/pci/pci.c              | 11 +++++++++--
>  include/hw/pci/pci_host.h |  1 +
>  2 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index 779787b..ac68065 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -392,9 +392,16 @@ bool pci_bus_is_root(PCIBus *bus)
>  
>  bool pci_allow_hybrid_pcie(PCIDevice *pci_dev)

Why are we asking the device about allowing hybrid pcie, and not
the bus itself? Shouldn't we be able to query this before the
device is plugged, and before pci_dev->bus is even set?

In other words, why pci_allow_hyberid_pcie() and
pci_device_get_bus() get a PCIDevice* argument instead of a
PCIBus* argument?

>  {
> -    PCIBus *bus = pci_dev->bus;
> +    PCIHostState *host_bridge = 
> PCI_HOST_BRIDGE(pci_device_root_bus(pci_dev)->qbus.parent);

There's something I don't understand completely: what exactly
guarantees that pci_device_root_bus(...)->qbus.parent is always
going to be a PCI_HOST_BRIDGE?

> +    PCIHostBridgeClass *hc = PCI_HOST_BRIDGE_GET_CLASS(host_bridge);
> +
> +    if (hc->allow_hybrid_pcie) {
> +        return hc->allow_hybrid_pcie(host_bridge, pci_dev);
> +    } else {
> +        PCIBus *bus = pci_dev->bus;
>  
> -    return pci_bus_is_express(bus) && !pci_bus_is_root(bus);
> +        return pci_bus_is_express(bus) && !pci_bus_is_root(bus);
> +    }
>  }
>  
>  void pci_bus_new_inplace(PCIBus *bus, size_t bus_size, DeviceState *parent,
> diff --git a/include/hw/pci/pci_host.h b/include/hw/pci/pci_host.h
> index ba31595..ad03cca 100644
> --- a/include/hw/pci/pci_host.h
> +++ b/include/hw/pci/pci_host.h
> @@ -54,6 +54,7 @@ typedef struct PCIHostBridgeClass {
>      SysBusDeviceClass parent_class;
>  
>      const char *(*root_bus_path)(PCIHostState *, PCIBus *);
> +    bool (*allow_hybrid_pcie)(PCIHostState *, PCIDevice *);
>  } PCIHostBridgeClass;
>  
>  /* common internal helpers for PCI/PCIe hosts, cut off overflows */
> -- 
> 2.9.3
> 
> 

-- 
Eduardo