High-level interrupts are those interrupts that interrupt at the level of the scheduler and above. This level does not allow the scheduler to run. Therefore, high-level interrupt handlers cannot be preempted by the scheduler. High-level interrupts cannot block because of the scheduler. High-level interrupts can only use mutual exclusion locks for locking.
The driver must determine whether the device is using high-level interrupts. Do this test in the driver's attach(9E) entry point when you register interrupts. See High-Level Interrupt Handling Example.
If the interrupt priority returned from ddi_intr_get_pri(9F) is greater than or equal to the priority returned from ddi_intr_get_hilevel_pri(9F), the driver can fail to attach, or the driver can implement a high-level interrupt handler. The high-level interrupt handler uses a lower-priority software interrupt to handle the device. To allow more concurrency, use a separate mutex to protect data from the high-level handler.
If the interrupt priority returned from ddi_intr_get_pri(9F) is less than the priority returned from ddi_intr_get_hilevel_pri(9F), the attach(9E) entry point falls through to regular interrupt registration. In this case, a soft interrupt is not necessary.