js/core/pci/scan.js
function locateAcpiDevice(dev) {
  if (!dev.isDevice()) {
    return null;
  }

  const addr = dev.address();
  const slotId = ((addr >>> 16) & 0xffff) >>> 0;
  const funcId = (addr & 0xffff) >>> 0;
  let busId = 0;

  if (dev.isRootBridge()) {
    busId = dev.getRootBridgeBusNumber();

    return {
      bus: busId,
      slot: slotId,
      func: funcId,
    };
  }

  const parentDev = dev.parent();
  if (parentDev === null) {
    return null;
  }

  if (!parentDev.isDevice()) {
    return null;
  }

  if (parentDev.isRootBridge()) {
    busId = parentDev.getRootBridgeBusNumber();

    return {
      bus: busId,
      slot: slotId,
      func: funcId,
    };
  }

  const parentLocation = locateAcpiDevice(parentDev);
  if (parentLocation === null) {
    return null;
  }

  const pciParent = pciAccessorFactory.get({
    bus: parentLocation.bus,
    slot: parentLocation.slot,
    func: parentLocation.func,
  });

  const header = pciParent.read(pciParent.fields().HEADER_TYPE);

  // Mask multifunction bit
  const headerType = (header & 0x7f) >>> 0;
  if (headerType !== 0x01 && headerType !== 0x02) {
    return null;
  }

  const bridgeBus = pciParent.read(pciParent.bridgeFields().SECONDARY_BUS);

  return {
    bus: bridgeBus,
    slot: slotId,
    func: funcId,
  };
}
function locateAcpiDevice(dev) {
  if (!dev.isDevice()) {
    return null;
  }

  const addr = dev.address();
  const slotId = ((addr >>> 16) & 0xffff) >>> 0;
  const funcId = (addr & 0xffff) >>> 0;
  let busId = 0;

  if (dev.isRootBridge()) {
    busId = dev.getRootBridgeBusNumber();

    return {
      bus: busId,
      slot: slotId,
      func: funcId,
    };
  }

  const parentDev = dev.parent();
  if (parentDev === null) {
    return null;
  }

  if (!parentDev.isDevice()) {
    return null;
  }

  if (parentDev.isRootBridge()) {
    busId = parentDev.getRootBridgeBusNumber();

    return {
      bus: busId,
      slot: slotId,
      func: funcId,
    };
  }

  const parentLocation = locateAcpiDevice(parentDev);
  if (parentLocation === null) {
    return null;
  }

  const pciParent = pciAccessorFactory.get({
    bus: parentLocation.bus,
    slot: parentLocation.slot,
    func: parentLocation.func,
  });

  const header = pciParent.read(pciParent.fields().HEADER_TYPE);

  // Mask multifunction bit
  const headerType = (header & 0x7f) >>> 0;
  if (headerType !== 0x01 && headerType !== 0x02) {
    return null;
  }

  const bridgeBus = pciParent.read(pciParent.bridgeFields().SECONDARY_BUS);

  return {
    bus: bridgeBus,
    slot: slotId,
    func: funcId,
  };
}
Find ACPI PCI device bus, slot and function