3.10 UEFI driver model

The Overview and UEFI Driver Model chapters of the UEFI Specification define the UEFI driver model. Drivers that follow the UEFI driver model share the same image characteristics as UEFI applications. However, the model allows UEFI more control over drivers by separating their loading into memory from their starting and stopping. The table below lists the series of UEFI driver model-related protocols that are used to accomplish this separation.
Table 10-Protocols separating the loading and starting/stopping of drivers
Protocol
Description
Driver Binding Protocol
Provides functions for starting and stopping the driver, as well as a function for determining if the driver can manage a particular controller. The UEFI driver binding model requires this protocol.
Service Binding Protocols
Provides a mechanism that allows protocols to support more than one consumer. UEFI Drivers that are required to produce protocols that need to be available to more than one consumer produce both the Driver Binding Protocol and a Service Binding Protocol.
Driver Supported EFI Version Protocol
Provides information on the version of the UEFI Specification to which the UEFI Driver conforms. The version information follows the same format as the version field in the EFI System Table.
Driver Family Override Protocol
Provides a mechanism for a UEFI Driver to express UEFI Driver specific version information among a family of UEFI Drivers that are used by ConnectController() to select the best driver to manage a specific controller.
Driver Health Protocol
Provides services that allow a UEFI Driver to express messages associated with the health status of a controller, suggest repair operations, and request configuration changes required to place the controller in a usable state.
HII Config Access Protocol
Provides services to retrieve and save configuration data for a controller managed by a UEFI Driver. Also provides a service that allows a setup browser to inform a UEFI Driver when specific setup browser actions are performed.
HII Packages
Allows a UEFI Driver to register strings, fonts, images, keyboard mappings, and setup forms related to the configuration operations required for UEFI Driver managed controllers.
Component Name 2 Protocol
Provides functions for retrieving a human-readable name of a driver and the controllers that a driver is managing using language codes defined by RFC 4646.
Driver Diagnostics 2 Protocols
Provides functions for executing diagnostic functions on driver managed devices using RFC 4646 defined language codes.
Component Name Protocol
Provides functions for retrieving a human-readable name of a driver and the controllers that a driver is managing using language codes defined by ISO 639-2. This protocol is only required by a UEFI Driver that must be compatible with platforms that support only UEFI 2.0 or EFI 1.10 This protocol has been replaced by the Component Name 2 Protocol.
Driver Diagnostics Protocols
Provides functions for executing diagnostic functions on driver managed devices using language codes defined by ISO 639-2. This protocol is only required by a UEFI Driver specifically compatible with platforms supporting only UEFI 2.0 or EFI 1.10 This protocol has been replaced by the Driver Diagnostics 2 Protocol.
Driver Configuration Protocol
Provides functions that allow users to configure devices a driver is managing using language codes defined by ISO 639-2. It also provides services to place a device into a default configuration. This protocol is only required by a UEFI Driver specifically compatible with platforms supporting only UEFI 2.0 or EFI 1.10.  This protocol has been replaced with HII functionality.
The new protocols are registered on the driver's image handle. HII packages are registered in the HII database. In the UEFI driver model, the main goal of the driver's entry point is to install theses protocols, register HII packages, and exit successfully.
At a later point in the system initialization, UEFI can use these protocol functions to operate the driver. A more complex driver may produce more than one instance of the EFI_DRIVER_BINDING_PROTOCOL. In this case, additional instances of the Driver Binding Protocol are installed on new handles. These new handles may also optionally support the additional protocols listed in Table 10 above.
The UEFI driver model follows the organization of physical/electrical architecture by defining three basic types of UEFI boot time drivers:
Device drivers
Bus drivers
Hybrid drivers, which have characteristics of both a device driver and a bus driver
Device drivers and bus drivers are distinguished by the operations they perform in the Start() and Stop() services of the Driver Binding Protocol. By walking through the
process of connecting a driver to a device, the roles and relationships of the bus drivers and device drivers become evident; the following sections discuss these two driver types.

3.9.3 Environment variables

3.10.1 Device driver

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