UEFI : DXE Driver

● 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。