Interrupt Request Interfaces

A driver must use the following interfaces to request interrupt vectors from the system.

Table 8–2 Interrupt Vector Request Interfaces

Interface	Data Structures	Description
ddi_intr_alloc()	ddi_intr_handle_t	Allocate interrupts.
ddi_intr_set_nreq()		Change number of interrupt vectors requested.

Allocate an Interrupt

Use the ddi_intr_alloc(9F) function to initially allocate interrupts.

int
ddi_intr_alloc (dev_info_t *dip, ddi_intr_handle_t *h_array, int type,
                int inum, int count, int *actualp, int behavior);

Before calling this function, the driver must allocate an empty handle array large enough to contain the number of interrupts requested. The ddi_intr_alloc() function attempts to allocate count number of interrupt handles, and initialize the array with the assigned interrupt vectors beginning at the offset specified by the inum parameter. The actualp parameter returns the actual number of interrupt vectors that were allocated.

A driver can use the ddi_intr_alloc() function in two ways:

• The driver can call the ddi_intr_alloc() function multiple times to allocate interrupt vectors to individual members of the interrupt handle array in separate steps.

• The driver can call the ddi_intr_alloc() function one time to allocate all of the interrupt vectors for the device at once.

If you are using the Interrupt Resource Management feature, call ddi_intr_alloc() one time to allocate all interrupt vectors at once. The count parameter is the total number of interrupt vectors requested by the driver. If the value in actualp is less than the value of count, then the system is not able to fulfill the request completely. The Interrupt Resource Management feature saves this request (count becomes nreq - see below) and might be able to allocate more interrupt vectors to this driver at a later time.

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Note –

When you use the Interrupt Resource Management feature, additional calls to ddi_intr_alloc() do not change the total number of interrupt vectors requested. Use the ddi_intr_set_nreq(9F) function to change the number of interrupt vectors requested.

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Modify Number of Interrupt Vectors Requested

Use the ddi_intr_set_nreq(9F) function to change the number of interrupt vectors requested.

int
ddi_intr_set_nreq (dev_info_t *dip, int nreq);

When the Interrupt Resource Management feature is available, a driver can use the ddi_intr_set_nreq() function to dynamically adjust the total number of interrupt vectors requested. The driver might do this in response to the actual load that exists once the driver is attached.

A driver must first call ddi_intr_alloc(9F) to request an initial number of interrupt vectors. Any time after the ddi_intr_alloc()call, the driver can call ddi_intr_set_nreq() to change its request size. The specified nreq value is the driver's new total number of requested interrupt vectors. The Interrupt Resource Management feature might rebalance the number of interrupts allocated to each driver in the system in response to this new request. Whenever the Interrupt Resource Management feature rebalances the number of interrupts allocated to drivers, each affected driver receives a callback notification that more or fewer interrupt vectors are available for the driver to use.

A driver might dynamically adjust its total number of requested interrupt vectors if, for example, it uses interrupts in conjunction with specific transactions that it is processing. A storage driver might associate a DMA engine with each ongoing transaction, thus requiring interrupt vectors for that reason. A driver might make calls to ddi_intr_set_nreq() in its open(9F) and close(9F) routines to scale its interrupt usage in response to actual use of the driver.

Interrupt Usage and Flexibility

A driver for a device that supports many different interruptible conditions must be able to map those conditions to an arbitrary number of interrupt vectors. The driver cannot assume that interrupt vectors that are allocated will remain available. Some currently available interrupts might later be taken back by the system to accommodate the needs of other drivers in the system.

A driver must be able to:

• Determine how many interrupts its hardware supports.

• Determine how many interrupts are appropriate to use. For example, the total number of processors in the system might affect this evaluation.

• Compare the number of interrupts needed with the number of interrupts available at any given time.

In summary, the driver must be able to select a mixture of interrupt handling functions and program its hardware to generate interrupts according to need and interrupt availability. In some cases multiple interrupts might be targeted to the same vector, and the interrupt handler for that interrupt vector must determine which interrupts occurred. The performance of the device can be affected by how well the driver maps interrupts to interrupt vectors.