18 PCI Driver Design Guidelines

There are several categories of PCI drivers that cooperate to provide support for PCI controllers in a platform. Table 25- lists these PCI drivers.

Table 25-Classes of PCI drivers

Class of driver

Description

PCI root bridge driver

Produces one or more instances of the PCI Root Bridge I/O Protocol.

PCI bus driver

Consumes the PCI Root Bridge I/O Protocol, produces a child handle for each PCI controller, and installs the Device Path Protocol and the PCI I/O Protocol onto each child handle.

PCI driver

Consumes the PCI I/O Protocol and produces an I/O abstraction providing services for the console and boot devices required to boot an EFI-conformant operating system.

This chapter concentrates on the design and implementation of PCI drivers. PCI drivers must follow all of the general design guidelines described in Chapter 4. This chapter covers guidelines that apply specifically to the management of PCI controllers.

The following figure shows an example PCI driver stack and the protocols the PCIrelated drivers consume and produce. In this example, the platform hardware produces a single PCI root bridge. The PCI Root Bridge I/O Protocol driver accesses the hardware resources to produce a single handle with the EFI_DEVICE_PATH_PROTOCOL and the EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL.

The PCI bus driver consumes the services of the PCI_ROOT_BRIDGE_IO_PROTOCOL and uses those services to enumerate the PCI controllers present in the system. In this example, the PCI bus driver detected a disk controller, a graphics controller, and a USB host controller. As a result, the PCI bus driver produces three child handles with the EFI_DEVICE_PATH_PROTOCOL and the EFI_PCI_IO_PROTOCOL.

  • The driver for the PCI disk controller consumes the services of the

    EFI_PCI_IO_PROTOCOL and produces two child handles with the

    EFI_DEVICE_PATH_PROTOCOL and the EFI_BLOCK_IO_PROTOCOL.

  • The PCI driver for the graphics controller consumes the services of the

    EFI_PCI_IO_PROTOCOL and produces a child handle with the

    EFI_GRAPHICS_OUTPUT_PROTOCOL.

  • The PCI driver for the USB host controller consumes the services of the

    EFI_PCI_IO_PROTOCOL to produce the EFI_USB_HOST_CONTROLLER_PROTOCOL.

    Although not shown in Figure 19, the EFI_USB_HOST_CONTROLLER_PROTOCOL would

    then be consumed by the USB bus driver to produce child handles for each USB

    device. USB drivers would then manage those child handles.

Chapter 19 contains the guidelines for designing USB drivers.

Figure 19-PCI driver stack