The detach() Entry Point

The kernel calls a driver's detach(9E) entry point to detach an instance of a device or to suspend operation for an instance of a device by power management. This section discusses the operation of detaching device instances. Refer to Chapter 9, Power Management for a discussion of power management issues.

A driver's detach() entry point is called to detach an instance of a device that is bound to the driver. The entry point is called with the instance of the device node to detach and DDI_DETACH specified as the cmd argument to the entry point.

A driver is required to cancel or wait for any time-outs or callbacks to complete, then release any resources that are allocated to the device instance before returning. If for some reason a driver cannot cancel outstanding callbacks for free resources, the driver is required to return the device to its original state and return DDI_FAILURE from the entry point, leaving the device instance in the attached state.

There are two types of callback routines: those that can be canceled and those that cannot. timeout(9F) and bufcall(9F) callbacks can be atomically cancelled by the driver during detach(9E). Other types of callbacks such as scsi_init_pkt(9F) and ddi_dma_buf_bind_handle(9F) cannot be canceled, requiring the driver to either block in detach() until the callback completes or to fail the request to detach.

Example 5–6 detach(9E) Routine

/*
 * detach(9e)
 * free the resources that were allocated in attach(9e)
 */
static int
xxdetach(dev_info_t *dip, ddi_detach_cmd_t cmd)
{
    Pio     *pio_p;
    int     instance;

    switch (cmd) {
    case DDI_DETACH:

        instance = ddi_get_instance(dip);
        pio_p = ddi_get_soft_state(pio_softstate, instance);

        /*
         * turn off the device
         * free any resources allocated in attach
         */
        ddi_put8(pio_p->csr_handle, pio_p->csr, PIO_RESET);

        ddi_remove_minor_node(dip, NULL);
        ddi_regs_map_free(&pio_p->csr_handle);
        ddi_regs_map_free(&pio_p->data_handle);
        ddi_remove_intr(pio_p->dip, 0, pio_p->iblock_cookie);
        mutex_destroy(&pio_p->mutex);
        ddi_soft_state_free(pio_softstate, instance);
        return (DDI_SUCCESS);

    case DDI_SUSPEND:
    default:
        return (DDI_FAILURE);
    }
}