Writing Device Drivers

Autoconfiguration Entry Points

Associated with each device driver is a dev_ops(9S) structure, which enables the kernel to locate the autoconfiguration entry points of the driver. A complete description of these autoconfiguration routines is given in Chapter 6, Driver Autoconfiguration. This section describes only those entry points associated with operations performed by SCSI HBA drivers. These entry points include attach(9E) and detach(9E).

attach() Entry Point (SCSI HBA Drivers)

The attach(9E) entry point for a SCSI HBA driver performs several tasks when configuring and attaching an instance of the driver for the device. For a typical driver of real devices, the following operating system and hardware concerns must be addressed:

Soft-State Structure

When allocating the per-device-instance soft-state structure, a driver must clean up carefully if an error occurs.


The HBA driver must describe the attributes of its DMA engine by properly initializing the ddi_dma_attr_t structure.

static ddi_dma_attr_t isp_dma_attr = {
     DMA_ATTR_V0,        /* ddi_dma_attr version */
     0,                  /* low address */
     0xffffffff,         /* high address */
     0x00ffffff,         /* counter upper bound */
     1,                  /* alignment requirements */
     0x3f,               /* burst sizes */
     1,                  /* minimum DMA access */
     0xffffffff,         /* maximum DMA access */
     (1<<24)-1,          /* segment boundary restrictions */
     1,                  /* scatter-gather list length */
     512,                /* device granularity */
     0                   /* DMA flags */

The driver, if providing DMA, should also check that its hardware is installed in a DMA-capable slot:

if (ddi_slaveonly(dip) == DDI_SUCCESS) {
    return (DDI_FAILURE);

Transport Structure

The driver should further allocate and initialize a transport structure for this instance. The tran_hba_private field is set to point to this instance's soft-state structure. The tran_tgt_probe field can be set to NULL to achieve the default behavior, if no special probe customization is needed.

tran = scsi_hba_tran_alloc(dip, SCSI_HBA_CANSLEEP);

isp->isp_tran                   = tran;
isp->isp_dip                    = dip;

tran->tran_hba_private          = isp;
tran->tran_tgt_private          = NULL;
tran->tran_tgt_init             = isp_tran_tgt_init;
tran->tran_tgt_probe            = scsi_hba_probe;
tran->tran_tgt_free             = (void (*)())NULL;

tran->tran_start                = isp_scsi_start;
tran->tran_abort                = isp_scsi_abort;
tran->tran_reset                = isp_scsi_reset;
tran->tran_getcap               = isp_scsi_getcap;
tran->tran_setcap               = isp_scsi_setcap;
tran->tran_init_pkt             = isp_scsi_init_pkt;
tran->tran_destroy_pkt          = isp_scsi_destroy_pkt;
tran->tran_dmafree              = isp_scsi_dmafree;
tran->tran_sync_pkt             = isp_scsi_sync_pkt;
tran->tran_reset_notify         = isp_scsi_reset_notify;
tran->tran_bus_quiesce          = isp_tran_bus_quiesce
tran->tran_bus_unquiesce        = isp_tran_bus_unquiesce
tran->tran_bus_reset            = isp_tran_bus_reset
tran->tran_interconnect_type    = isp_tran_interconnect_type

Attaching an HBA Driver

The driver should attach this instance of the device, and perform error cleanup if necessary.

i = scsi_hba_attach_setup(dip, &isp_dma_attr, tran, 0);
if (i != DDI_SUCCESS) {
    /* do error recovery */
    return (DDI_FAILURE);

Register Mapping

The driver should map in its device's registers. The driver need to specify the following items:

ddi_device_acc_attr_t    dev_attributes;

     dev_attributes.devacc_attr_version = DDI_DEVICE_ATTR_V0;
     dev_attributes.devacc_attr_dataorder = DDI_STRICTORDER_ACC;
     dev_attributes.devacc_attr_endian_flags = DDI_STRUCTURE_LE_ACC;

     if (ddi_regs_map_setup(dip, 0, (caddr_t *)&isp->isp_reg,
     0, sizeof (struct ispregs), &dev_attributes,
     &isp->isp_acc_handle) != DDI_SUCCESS) {
        /* do error recovery */
        return (DDI_FAILURE);

Adding an Interrupt Handler

The driver must first obtain the iblock cookie to initialize any mutexes that are used in the driver handler. Only after those mutexes have been initialized can the interrupt handler be added.

i = ddi_get_iblock_cookie(dip, 0, &isp->iblock_cookie};
if (i != DDI_SUCCESS) {
    /* do error recovery */
    return (DDI_FAILURE);

mutex_init(&isp->mutex, "isp_mutex", MUTEX_DRIVER,
(void *)isp->iblock_cookie);
i = ddi_add_intr(dip, 0, &isp->iblock_cookie,
0, isp_intr, (caddr_t)isp);
if (i != DDI_SUCCESS) {
    /* do error recovery */
    return (DDI_FAILURE);

If a high-level handler is required, the driver should be coded to provide such a handler. Otherwise, the driver must be able to fail the attach. See Handling High-Level Interrupts for a description of high-level interrupt handling.

Create Power Manageable Components

With power management, if the host bus adapter only needs to power down when all target adapters are at power level 0, the HBA driver only needs to provide a power(9E) entry point. Refer to Chapter 12, Power Management. The HBA driver also needs to create a pm-components(9P) property that describes the components that the device implements.

Nothing more is necessary, since the components will default to idle, and the power management framework's default dependency processing will ensure that the host bus adapter will be powered up whenever an target adapter is powered up. Provided that automatic power management is enabled automatically, the processing will also power down the host bus adapter when all target adapters are powered down ().

Report Attachment Status

Finally, the driver should report that this instance of the device is attached and return success.

    return (DDI_SUCCESS);

detach() Entry Point (SCSI HBA Drivers)

The driver should perform standard detach operations, including calling scsi_hba_detach(9F).