Intel Extensible Firmware Interface - Manual (Page 575)

Protocols — USB Support
Version 1.10 12/01/02 14-35
In the USB Bus Driver Design, the USB Bus Controller is managed by two drivers. One is USB
Host Controller Driver, which consumes its parent bus
EFI_XYZ_IO_PROTOCOL , and produces
EFI_USB_HC_PROTOCOL and attaches it to the Bus Controller Handle. The other one is USB
Bus Driver, which consumes EFI_USB_HC_PROTOCOL , and performs bus enumeration.
Figure 14-2 shows protocols that are attached to the USB Bus Controller Handle. Detailed
descriptions are presented in the following sections.
14.2.3 USB Bus Driver
USB Bus Driver performs periodic Enumeration on the USB Bus. In USB bus enumeration, when
a new USB controller is found, the bus driver does some standard configuration for that new
controller, and creates a device handle for it. The
EFI_USB_IO_PROTOCOL and the
EFI_DEVICE_PATH are attached to the device handle so that the USB controller can be accessed.
The USB Bus Driver is also responsible for connecting USB device drivers to USB controllers.
When a USB device is detached from a USB bus, the USB bus driver will stop that USB controller,
and uninstall the
EFI_USB_IO_PROTOCOL and the EFI_DEVICE_PATH from that handle. A
detailed description is given in Section 14.2.3.3.
14.2.3.1 USB Bus Driver Entry Point
Like all other device drivers, the entry point for a USB Bus Driver attaches the
EFI_DRIVER_BINDING_PROTOCOL to image handle of the USB Bus Driver.
14.2.3.2 Driver Binding Protocol for USB Bus Drivers
The Driver Binding Protocol contains three services. These are Supported() , Start() , and
Stop() . Supported() tests to see if the USB Bus Driver can manage a device handle. A USB
Bus Driver can only manage a device handle that contains EFI_USB_HC_PROTOCOL .
The general idea is that the USB Bus Driver is a generic driver. Since there are several types of
USB Host Controllers, an
EFI_USB_HC_PROTOCOL is used to abstract the host controller
interface. Actually, a USB Bus Driver only requires an EFI_USB_HC_PROTOCOL .
The Start() function tells the USB Bus Driver to start managing the USB Bus. In this function,
the USB Bus Driver creates a device handle for the root hub, and creates a timer to monitor root
hub connection changes.
The Stop() function tells the USB Bus Driver to stop managing a USB Host Bus Controller. The
Stop() function simply deconfigures the devices attached to the root hub. The deconfiguration is
a recursive process. If the device to be deconfigured is a USB hub, then all USB devices attached
to its downstream ports will be deconfigured first, then itself. If all of the child devices handles
have been destroyed then the
EFI_USB_HC_PROTOCOL is closed. Finally, the Stop() unction
will then place the USB Host Bus Controller in a quiescent state.