High-Level Interrupts

Buses prioritize device interrupts at one of several bus-interrupt levels. These bus interrupt levels are then mapped to different processor-interrupt levels. A bus interrupt level that maps to a CPU interrupt priority level above the scheduler priority level is called a high-level interrupt. High-level interrupt handlers are restricted to what DDI interfaces they can call. In particular, the only DDI routines that high-level interrupt handlers are allowed to call are:

• mutex_enter(9F) and mutex_exit(9F) on a mutex initialized with an iblock cookie associated with the high-level interrupt

• ddi_trigger_softintr(9F)

• ddi_getX/ddi_putX family of routines

A bus-interrupt level by itself does not determine whether a device interrupts at high level: a given bus-interrupt level may map to a high-level interrupt on one platform, but map to an ordinary interrupt on another platform.

The driver can choose whether to support devices that have high-level interrupts, but it always has to check--it cannot assume that its interrupts are not high level. The function ddi_intr_hilevel(9F), given an interrupt number, returns a value indicating whether the interrupt is high level.