pci: Introduce helper to retrieve a PCI device's DMA address space

A PCI device's DMA address space (possibly an IOMMU) is returned by a
method on the PCIBus.  At the moment that only has one caller, so the
method is simply open coded.  We'll need another caller for VFIO, so
this patch introduces a helper/wrapper function.

If IOMMU is not set, the pci_device_iommu_address_space() function
returns the parent's IOMMU skipping the "bus master" address space as
otherwise proper emulation would require more effort for no benefit.
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>
[aik: added inheritance from parent if iommu is not set for the current bus]
Signed-off-by: NAlexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/pci/pci.c

@@ -812,12 +812,7 @@ static PCIDevice *do_pci_register_device(PCIDevice *pci_dev, PCIBus *bus,
     }
 
     pci_dev->bus = bus;
-    if (bus->iommu_fn) {
-        dma_as = bus->iommu_fn(bus, bus->iommu_opaque, devfn);
-    } else {
-        /* FIXME: inherit memory region from bus creator */
-        dma_as = &address_space_memory;
-    }
+    dma_as = pci_device_iommu_address_space(pci_dev);
 
     memory_region_init_alias(&pci_dev->bus_master_enable_region,
                              OBJECT(pci_dev), "bus master",
@@ -2239,6 +2234,23 @@ static void pci_device_class_init(ObjectClass *klass, void *data)
     k->props = pci_props;
 }
 
+AddressSpace *pci_device_iommu_address_space(PCIDevice *dev)
+{
+    PCIBus *bus = PCI_BUS(dev->bus);
+
+    if (bus->iommu_fn) {
+        return bus->iommu_fn(bus, bus->iommu_opaque, dev->devfn);
+    }
+
+    if (bus->parent_dev) {
+        /** We are ignoring the bus master DMA bit of the bridge
+         *  as it would complicate things such as VFIO for no good reason */
+        return pci_device_iommu_address_space(bus->parent_dev);
+    }
+
+    return &address_space_memory;
+}
+
 void pci_setup_iommu(PCIBus *bus, PCIIOMMUFunc fn, void *opaque)
 {
     bus->iommu_fn = fn;

include/hw/pci/pci.h

@@ -405,6 +405,7 @@ void pci_device_deassert_intx(PCIDevice *dev);
 
 typedef AddressSpace *(*PCIIOMMUFunc)(PCIBus *, void *, int);
 
+AddressSpace *pci_device_iommu_address_space(PCIDevice *dev);
 void pci_setup_iommu(PCIBus *bus, PCIIOMMUFunc fn, void *opaque);
 
 static inline void