Intel Extensible Firmware Interface Manuel d'utilisateur télécharger pdf (Page 65)

Overview

Version 1.10 12/01/02 2-25

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Bus Controller

Start()

Stop()

ABCDE

Figure 2-12. Connecting Bus Drivers

A bus driver that supports creating one child on each call to Start() might choose to create child

C first, and then child E, and then the remaining children A, B, and D. The Supported()

Start(),andStop()

functions of the Driver Binding Protocol are flexible enough to allow this

type of behavior.

A bus driver must install protocol interfaces onto every child handle that is creates. At a minimum,

it must install a protocol interface that provides an I/O abstraction of the bus’s services to the child

controllers. If the bus driver creates a child handle that represents a physical device, then the bus

driver must also install a Device Path Protocol instance onto the child handle. A bus driver may

optionally install a Bus Specific Driver Override Protocol onto each child handle. This protocol is

used when drivers are connected to the child controllers. The boot service

ConnectController()

uses architecturally defined precedence rules to choose the best set of

drivers for a given controller. The Bus Specific Driver Override Protocol has higher precedence

than a general driver search algorithm, and lower precedence than platform overrides. An example

of a bus specific driver selection occurs with PCI. A PCI Bus Driver gives a driver stored in a PCI

controller’s option ROM a higher precedence than drivers stored elsewhere in the platform.

Figure 2-13 shows an example child device handle that was created by the XYZ Bus Driver that

supports a bus specific driver override mechanism.

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Intel Extensible Firmware Interface Manuel d'utilisateur Page 65