Man page 9 : pci_bus_find_capability

pci_bus_find_capability - query for devicesAq capabilities

int pci_bus_find_capability(struct pci_bus *  bus , unsigned int  devfn , int  cap );

bus
    the PCI bus to query

devfn
    PCI device to query

cap
    capability code

Like pci_find_capability but works for pci devices that do not have a pci_dev structure set up yet.

Returns the address of the requested capability structure within the deviceAqs PCI configuration space or 0 in case the device does not support it.