How do I find whatever combination of things end up defining pcib_get_bus(. . .)?

# grep -r "\<pcib_get_bus\>" /usr/13S-src/ | more
/usr/13S-src/sys/mips/nlm/xlp_pci.c:    busno = pcib_get_bus(dev);
/usr/13S-src/sys/powerpc/ofw/ofw_pcibus.c:      busno = pcib_get_bus(dev);
/usr/13S-src/sys/dev/pci/pci.c: busno = pcib_get_bus(dev);
/usr/13S-src/sys/dev/pci/pci.c: busno = pcib_get_bus(dev);
/usr/13S-src/sys/dev/pci/pci.c: busno = pcib_get_bus(dev);
/usr/13S-src/sys/dev/cardbus/cardbus.c:     pcib_get_bus(cbdev), pcib_get_bus(cbdev), 1, 0);
/usr/13S-src/sys/dev/cardbus/cardbus.c: bus = pcib_get_bus(cbdev);
/usr/13S-src/sys/dev/hyperv/pcib/vmbus_pcib.c:  busno = pcib_get_bus(dev);
/usr/13S-src/sys/dev/pccbb/pccbb.c:             b = pcib_get_bus(child);
/usr/13S-src/sys/dev/pccbb/pccbb_pci.c: sc->pribus = pcib_get_bus(parent);
/usr/13S-src/sys/x86/pci/qpi.c:         *result = pcib_get_bus(dev);
/usr/13S-src/sys/x86/pci/pci_bus.c:     bus = pcib_get_bus(dev);
/usr/13S-src/sys/x86/iommu/intel_drv.c:                 *busno = pcib_get_bus(bus);

Everything found is a use, not a definition. (I also tried:
# grep -r "\<pcib_get_bus\>" /usr/obj/BUILDs/13S-CA72-nodbg-clang/ .)

Historically I've managed to eventually track down definitions
are are less direct, such as ones that are formed via macros
that put together names. But, so far, I've not managed to for
pcib_get_bus .

So, hopefully, someone can point me to what I've missed.

===
Mark Millard
marklmi at yahoo.com