21.1.2 Implementing ATA Pass Thru Protocol

EFI_ATA_PASS_THRU_PROTOCOL allows information about a ATA target to be collected and allows ATA Request Packets to be sent to any ATA devices connected to the ATA host controller, even if those devices are not boot devices. This protocol is attached to the device handle of the ATA host controller in a system that the protocol supports and can be used for diagnostics. It may also be used to build a block I/O driver for ATA hard drives allowing those devices to be used as boot devices. The ATA Pass Thru Protocol is usually implemented in the file AtaPassThru.c. Appendix A contains a template for the ATA Pass Thru Protocol.

Example 220-ATA Pass Thru Protocol

typedef struct _EFI_ATA_PASS_THRU_PROTOCOL EFI_ATA_PASS_THRU_PROTOCOL;
struct _EFI_ATA_PASS_THRU_PROTOCOL {
EFI_ATA_PASS_THRU_MODE *Mode;
EFI_ATA_PASS_THRU_PASSTHRU PassThru;
EFI_ATA_PASS_THRU_GET_NEXT_PORT GetNextPort;
EFI_ATA_PASS_THRU_GET_NEXT_DEVICE GetNextDevice;
EFI_ATA_PASS_THRU_BUILD_DEVICE_PATH BuildDevicePath;
EFI_ATA_PASS_THRU_GET_DEVICE GetDevice;
EFI_ATA_PASS_THRU_RESET_PORT ResetPort;
EFI_ATA_PASS_THRU_RESET_DEVICE ResetDevice;
};

For a detailed description of EFI_ATA_PASS_THRU_PROTOCOL, see the ATA Pass Thru Protocol section of the UEFI Specification.

Before implementing ATA Pass Thru Protocol, the ATA host controller driver configures the ATA host controller to a defined state. In practice, the ATA host controller maps a set of ATA host controller registers in I/O or memory-mapped I/O space. Although the detailed layout or functions of these registers vary from one ATA host controller to another, the ATA host controller driver uses specific knowledge to set up the proper ATA mode and configure the timing registers for the current mode. Other considerations include DMA engine and interrupt initialization, among others.

All the hardware-related settings must be completed before any ATA Pass Thru Protocol functions are called. The initialization is usually performed in the Driver Binding Protocol's Start() function of the ATA host controller driver prior to installing the ATA Pass Thru Protocol instance into the Handle Database.

EFI_ATA_PASS_THRU_PROTOCOL.Mode is a structure that describes the intrinsic attributes of the ATA Pass Thru Protocol instance. Note that a non-RAID ATA host controllers set both the physical and logical attributes. A physical channel on the RAID sets only the physical attribute, and the logical channel on the RAID adapter sets only the logical attribute. If the channel supports non-blocking I/O, the non-blocking attribute is also set. The example below shows how to set those attributes on a non-RAID ATA host controller that supports non-blocking I/O.

Example 221-ATA Pass Thru Mode Structure

//
// The channel does support nonblocking I/O
//
AtaPassThruMode.Attributes = EFI_ATA_PASS_THRU_ATTRIBUTES_PHYSICAL |
EFI_ATA_SCSI_PASS_THRU_ATTRIBUTES_LOGICAL |
EFI_ATA_SCSI_PASS_THRU_ATTRIBUTES_NONBLOCKIO;
//
// Do not have any alignment requirement
//
AtaPassThruMode.IoAlign = 0;

The example below shows how to set the ATA Mode structures for an ATA host controller that provides RAID capabilities and produced an ATA Pass Thru Protocol instance for accessing the physical drives and another ATA Pass Thru Protocol instance for accessing the logical drives.

Example 222-SCSI Pass Thru Mode Structures for RAID SCSI adapter

//
// ...... Physical Channel ......
//
AtaPassThruMode.Attributes = EFI_ATA_PASS_THRU_ATTRIBUTES_PHYSICAL |
EFI_ATA_PASS_THRU_ATTRIBUTES_NONBLOCKIO;
AtaPassThruMode.IoAlign = 0;
//
// ...... Logical Channel ......
//
AtaPassThruMode.Attributes = EFI_ATA_PASS_THRU_ATTRIBUTES_LOGICAL |
EFI_ATA_PASS_THRU_ATTRIBUTES_NONBLOCKIO;
AtaPassThruMode.IoAlign = 0;

The EFI_ATA_PASS_THRU_PROTOCOL.GetNextPort() and EFI_ATA_PASS_THRU_PROTOCOL.GetNextDevice() functions provide the ability to enumerate all the ATA devices. EFI_ATA_PASS_THRU_PROTOCOL.BuildDevicePath() function facilitates the construction of an ATA device path.

The EFI_ATA_PASS_THRU_PROTOCOL.PassThru() function is the most important function when implementing ATA Pass Thru Protocol and it performs the following:

  • Initialize the internal register for command/data transfer.

  • Put valid ATA commands into hardware-specific memory or register locations.

  • Start the transfer.

  • Optionally wait for completion of the execution.

The better error handling mechanism in this function helps to develop a more robust driver. Although most ATA host controllers support both blocking and non-blocking data transfers, some may only support blocking transfers.