● 何謂Protocol:
typedef的結構。在UEFI下會綁定GUID，並且透過Driver來安裝Protocol instance到handle上. 上層若要控制device，必須透過呼叫Protocol instance來達成。
● Bus Driver Vs. Device Driver:
Bus Driver會Create Child handle 但Device Driver不會。如果Bus Driver Create的 Child handle是Physical device, Bus Driver 必須安裝Device Path Protocol instance到Child handle
● Driver Initialization:
Driver Image會從儲存裝置(Rom, flash,...)中載入,也就是說，一旦在儲存裝置中找到Driver Image, 就會使用Boot Service的LoadImage(), 將Driver Image載入到System Memory. 同時該driver會生成自己的Handle，並且在該Handle下安裝EFI_LOADED_IMAGE_PROTOCOL。
typedef
EFI_STATUS
LoadImage (
IN
BOOLEAN BootPolicy,
IN
EFI_HANDLE ParentImageHandle,
IN
EFI_DEVICE_PATH_PROTOCOL *DevicePath, // The DeviceHandle specific file path
from which the image is loaded.
IN
VOID *SourceBuffer OPTIONAL,
IN
UINTN SourceSize,
OUT
EFI_HANDLE *ImageHandle // Pointer to the returned image handle that is created
when the image is successfully loaded.
);
裝了EFI_LOADED_IMAGE_PROTOCOL 的Handle稱之為Image Handle。
接著，透過Boot Service的StartImage()來啟動driver，driver會在Image Handle上安裝其它的Protocol，如果是EFI Driver Model的driver，那麼會安裝EFI_DRIVER_BINDING_PROTOCOL, 如下，這時Driver Image才真正被當作Driver來處理
//
// Interface structure for the
ControllerHandle Driver Protocol
//
typedef struct _EFI_DRIVER_BINDING_PROTOCOL
{
EFI_DRIVER_BINDING_SUPPORTED
Supported;
EFI_DRIVER_BINDING_START
Start;
EFI_DRIVER_BINDING_STOP
Stop;
UINT32 Version;
EFI_HANDLE
ImageHandle;
EFI_HANDLE
DriverBindingHandle;
} EFI_DRIVER_BINDING_PROTOCOL;
LoadImage()和StartImage()做完之後，driver會等待被Boot Service的ConnectController()調用(invoked)去連接到某個Controller。這時在System Memory中已經Load了很多的Driver都在等待被connect到Controller，這時ConnectController()會以Polling的方式去調用每個Driver Handle中的EFI_DRIVER_BINDING_PROTOCOL.Supported()，如果回EFI_SUCCESS，那麼該driver就會被connect到controller上。之後會透過EFI_DRIVER_BINDING_PROTOCOL.Start()來初始化以及安裝特定的Protocol到此Controller。
