3.15.2 Connecting the PCI bus

Platform initialization continues by loading the PCI bus driver. As the driver's entry point is executed, the PCI bus driver installs the Driver Binding Protocol and potentially the Component Name Protocols.
For example, the handle database as viewed with the dh UEFI Shell command might look like the following after the PCI bus driver is loaded and started. It contains one new driver image handle with the Loaded Image Protocol, Driver Binding Protocol, and Component Name2 Protocol. Because this driver does follow the UEFI Driver Model, no new controller handles are produced when the driver is loaded and started. They are not produced until the driver is connected.
14: Image(PciBus) Driver Binding ComponentName
Later in the platform initialization process, UEFI-conformant firmware uses ConnectController() to attempt to connect the PCI root bridge controller(s) (handle #14 hex, as shown in the example above). The system has several priority rules for determining what driver to try first, but in this case it searches the handle database for driver handles (handles with the Driver Binding Protocol). The search finds handle #14 and call the Driver Binding Protocol Supported() service, passing in controller handle #14. The PCI bus driver requires the Device Path Protocol and PCI Root Bridge I/O Protocol to be started, so the Supported() service returns EFI_SUCCESS when those two protocols are found on handle #14 After receiving EFI_SUCCESS from the Supported() service, ConnectController() then calls the Driver Binding Protocol Start() service with the same controller handle #14.
Due to the PCI Bus Driver, the Start() service uses the PCI Root Bridge I/O Protocol functions to enumerate the PCI bus and discover all PCI devices. For each PCI device/function that the PCI bus driver discovers, it creates a child handle and installs an instance of the PCI I/O Protocol on the handle. The handle is registered in the handle database as a "child" of the PCI root bridge controller.
The PCI bus driver also copies the device path from the parent PCI root bridge device handle and appends a new PCI device path node Pci(Dev|Func). In cases where the PCI bus driver discovers a PCI-to-PCI bridge, the devices below the bridge are added as children to the bridge. In these cases, extra PCI device path nodes are added for each PCI-to-PCI bridge between the PCI root bridge and the PCI device.
For example, the handle database as viewed with the dh UEFI Shell command might look like the following after the PCI bus driver is connected to the PCI root bridge. It shows that:
  • Nine PCI devices were discovered.
  • The PCI device on handle #1B has an option ROM with a UEFI driver.
  • That UEFI driver was loaded and executed and is shown as handle #1C.
Also notice that a single PCI card may have several UEFI handles if they have multiple PCI functions.
16: PciIo DevPath (Acpi(HWP0002,0,PNP0A03)/Pci(1|0))
17: PciIo DevPath (Acpi(HWP0002,0,PNP0A03)/Pci(1|1))
18: PciIo DevPath (Acpi(HWP0002,0,PNP0A03)/Pci(2|0))
19: PciIo DevPath (Acpi(HWP0002,0,PNP0A03)/Pci(2|1))
1A: PciIo DevPath (Acpi(HWP0002,0,PNP0A03)/Pci(2|2))
1B: PciIo DevPath (Acpi(HWP0002,0,PNP0A03)/Pci(3|0))
1C: Image(Acpi(HWP0002,0,PNP0A03)/Pci(3|0)) Driver Binding
1D: PciIo DevPath (Acpi(HWP0002,0,PNP0A03)/Pci(4|0))
1E: PciIo DevPath (Acpi(HWP0002,100,PNP0A03)/Pci(1|0))
1F: PciIo DevPath (Acpi(HWP0002,100,PNP0A03)/Pci(1|1))