6.1.4 Device drivers with one driver binding protocol

Most device drivers produce a single instance of the EFI_DRIVER_BINDING_PROTOCOL. These drivers are the simplest among those that follow the UEFI driver model and all other driver types have their roots in this type of device driver.

A device driver is loaded into memory with the LoadImage() Boot Service and invoked with the StartImage() Boot Service. The LoadImage() service automatically creates an image handle and installs the EFI_LOADED_IMAGE_PROTOCOL onto the image handle. The EFI_LOADED_IMAGE_PROTOCOL describes the location from where the device driver was loaded and the location in system memory to where the device driver was placed. The Unload() service of the EFI_LOADED_IMAGE_PROTOCOL is initialized to NULL by LoadImage(). This setting means that by default the driver does not have an unload function.

The StartImage() service transfers control to the driver's entry point as described in the PE/COFF header of the UEFI Driver image. The PE/COFF header layout is defined in the Microsoft Portable Executable and Common Object File Format Specification.

The driver entry point is responsible for installing the Driver Binding Protocol onto the driver's image handle. The figure below shows the state of the system before a device driver is loaded, just before it is started, and after the driver's entry point has been executed.

Figure 9-Device driver with single Driver Binding Protocol

The following figure is the same as the figure above, except this device driver has also implemented optional features. This difference means the following:

  • Additional protocols are installed onto the driver's image handle.

  • An Unload() service is registered in the EFI_LOADED_IMAGE_PROTOCOL.

  • An Exit Boot Services event and Set Virtual Address Map event have been created. These are part of the driver's initialization (the driver's entry point).

Figure 10-Device driver with optional features