PCI_SECONDARY_BUS_MASK
secondary = FIELD_GET(PCI_SECONDARY_BUS_MASK, buses);
FIELD_PREP(PCI_SECONDARY_BUS_MASK, child->busn_res.start) |
res.start = FIELD_GET(PCI_SECONDARY_BUS_MASK, buses);
FIELD_PREP(PCI_SECONDARY_BUS_MASK, child->busn_res.start) |