Introduction to Host Bus Adapter Drivers

As described in Chapter 14, SCSI Target Drivers, the Solaris 9 DDI/DKI divides the software interface to SCSI devices into two major parts:

• Target devices and drivers

• Host bus adapter devices and drivers

Target device refers to a device on a SCSI bus, such as a disk or a tape drive. Target driver refers to a software component installed as a device driver. Each target device on a SCSI bus is controlled by one instance of the target driver.

Host bus adapter device refers to HBA hardware, such as an SBus or PCI SCSI adapter card. Host bus adapter driver refers to a software component installed as a device driver, such as the esp driver on a SPARC machine or the ncrs driver on an IA machine, and the isp driver, which works on both. An instance of the HBA driver controls each of its host bus adapter devices configured in the system.

The Sun Common SCSI Architecture (SCSA) defines the interface between these target and HBA components.

Understanding SCSI target drivers is an essential prerequisite to writing effective SCSI HBA drivers. For information on SCSI target drivers, see Chapter 14, SCSI Target Drivers. Target driver developers can also benefit from reading this chapter.

The host bus adapter driver is responsible for:

• Managing host bus adapter hardware

• Accepting SCSI commands from the SCSI target driver

• Transporting the commands to the specified SCSI target device

• Performing any data transfers that the command requires

• Collecting status

• Handling auto-request sense (optional)

• Informing the target driver of command completion (or failure)