Writing Device Drivers

attach() Entry Point

The syntax for attach(9E) is as follows:

int attach(dev_info_t *dip, ddi_attach_cmd_t cmd);

When power is restored to the system, each device with a reg property or with a pm-hardware-state property of value needs-suspend-resume has its attach(9E) entry point called with a command value of DDI_RESUME. If the system shutdown is aborted, each suspended driver is called to resume even though the power has not been shut off. Consequently, the resume code in attach(9E) must make no assumptions about whether the system actually lost power.

The power management framework considers the power level of the components to be unknown at DDI_RESUME time. Depending on the nature of the device, the driver writer has two choices:

The following example shows an attach(9E) routine with the DDI_RESUME command.

Example 12–7 attach(9E) Routine Implementing DDI_RESUME

xxattach(devinfo_t *dip, ddi_attach_cmd_t cmd)
    struct xxstate *xsp;
    int    instance;

    instance = ddi_get_instance(dip);
    xsp = ddi_get_soft_state(statep, instance);

    switch (cmd) {
    case DDI_ATTACH:
    /* ... */
    case DDI_RESUME:
        if (xsp->xx_pm_state_saved) {
             * Restore device register contents from
             * xsp->xx_device_state
        * This section is optional and only needed if the
        * driver maintains a running timeout
        xsp->xx_timeout_id = timeout( /* ... */ );

        xsp->xx_suspended = 0;        /* allow new operations */
       /* If it is possible to determine in a device-specific 
        * way what the power levels of components are without 
        * powering the components up,
        * then the following code is recommended
        for (i = 0; i < num_components; i++) {
            xsp->xx_power_level[i] = xx_get_power_level(dip, i);
            if (xsp->xx_power_level[i] != XX_LEVEL_UNKNOWN)
                (void) pm_power_has_changed(dip, i, 

Note –

The detach(9E) and attach(9E) interfaces can also be used to resume a system that has been quiesced.