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BUS_SETUP_INTR(9)	 BSD Kernel Developer's Manual	     BUS_SETUP_INTR(9)

NAME
     BUS_SETUP_INTR, bus_setup_intr, BUS_TEARDOWN_INTR, bus_teardown_intr —
     create, attach and teardown an interrupt handler

SYNOPSIS
     #include <sys/param.h>
     #include <sys/bus.h>

     int
     BUS_SETUP_INTR(device_t dev, device_t child, struct resource *irq,
	 int flags, driver_filter_t *filter, driver_intr_t *ithread,
	 void *arg, void **cookiep);

     int
     bus_setup_intr(device_t dev, struct resource *r, int flags,
	 driver_filter_t filter, driver_intr_t ithread, void *arg,
	 void **cookiep);

     int
     BUS_TEARDOWN_INTR(device_t dev, device_t child, struct resource *irq,
	 void *cookiep);

     int
     bus_teardown_intr(device_t dev, struct resource *r, void *cookiep);

DESCRIPTION
     The BUS_SETUP_INTR() method will create and attach an interrupt handler
     to an interrupt previously allocated by the resource manager's
     BUS_ALLOC_RESOURCE(9) method.  The flags are found in <sys/bus.h>, and
     give the broad category of interrupt.  The flags also tell the interrupt
     handlers about certain device driver characteristics.  INTR_EXCL marks
     the handler as being an exclusive handler for this interrupt.
     INTR_MPSAFE tells the scheduler that the interrupt handler is well
     behaved in a preemptive environment (``SMP safe''), and does not need to
     be protected by the ``Giant Lock'' mutex.	INTR_ENTROPY marks the inter‐
     rupt as being a good source of entropy - this may be used by the entropy
     device /dev/random.

     To define a time-critical handler (previously known as INTR_FAST) that
     will not execute any potentially blocking operation, use the filter argu‐
     ment.  See the Filter Routines section below for information on writing a
     filter.  Otherwise, use the ithread argument.  The defined handler will
     be called with the value arg as its only argument.	 See the ithread
     Routines section below for more information on writing an interrupt han‐
     dler.

     The cookiep argument is a pointer to a void * that BUS_SETUP_INTR() will
     write a cookie for the parent bus' use to if it is successful in estab‐
     lishing an interrupt.  Driver writers may assume that this cookie will be
     non-zero.	The nexus driver will write 0 on failure to cookiep.

     The interrupt handler will be detached by BUS_TEARDOWN_INTR().  The
     cookie needs to be passed to BUS_TEARDOWN_INTR() in order to tear down
     the correct interrupt handler.  Once BUS_TEARDOWN_INTR() returns, it is
     guaranteed that the interrupt function is not active and will no longer
     be called.

     Mutexes are not allowed to be held across calls to these functions.

   Filter Routines
     A filter runs in a context very similar to what was known as an INTR_FAST
     routine in previous versions of FreeBSD.  In this context, normal mutexes
     cannot be used.  Only the spin lock version of these can be used (speci‐
     fied by passing MTX_SPIN to mtx_init() when initializing the mutex).
     wakeup(9) and similar routines can be called.  Atomic operations from
     machine/atomic may be used.  Reads and writes to hardware through
     bus_space(9) may be used.	PCI configuration registers may be read and
     written.  All other kernel interfaces cannot be used.

     In this restricted environment, care must be taken to account for all
     races.  A careful analysis of races should be done as well.  It is gener‐
     ally cheaper to take an extra interrupt, for example, than to protect
     variables with spinlocks.	Read, modify, write cycles of hardware regis‐
     ters need to be carefully analyzed if other threads are accessing the
     same registers.

     Generally, a filter routine will use one of two strategies.  The first
     strategy is to simply mask the interrupt in hardware and allow the
     ithread routine to read the state from the hardware and then reenable
     interrupts.  The ithread also acknowledges the interrupt before re-
     enabling the interrupt source in hardware.	 Most PCI hardware can mask
     its interrupt source.

     The second common approach is to use a filter with multiple taskqueue(9)
     tasks.  In this case, the filter acknowledges the interrupts and queues
     the work to the appropriate taskqueue.  Where one has to multiplex dif‐
     ferent kinds of interrupt sources, like a network card's transmit and
     receive paths, this can reduce lock contention and increase performance.

     You should not malloc(9) from inside a filter.  You may not call anything
     that uses a normal mutex.	Witness may complain about these.

   ithread Routines
     You can do whatever you want in an ithread routine, except sleep.	Care
     must be taken not to sleep in an ithread.	In addition, one should mini‐
     mize lock contention in an ithread routine because contested locks ripple
     over to all other ithread routines on that interrupt.

   Sleeping
     Sleeping is voluntarily giving up control of your thread.	All the sleep
     routine found in msleep(9) sleep.	Waiting for a condition variable
     described in condvar(9) is sleeping.  Calling any function that does any
     of these things is sleeping.

RETURN VALUES
     Zero is returned on success, otherwise an appropriate error is returned.

SEE ALSO
     random(4), device(9), driver(9), mtx_init(9), wakeup(9)

AUTHORS
     This manual page was written by Jeroen Ruigrok van der Werven
     ⟨asmodai@FreeBSD.org⟩ based on the manual pages for BUS_CREATE_INTR() and
     BUS_CONNECT_INTR() written by Doug Rabson ⟨dfr@FreeBSD.org⟩.

BSD			       December 18, 2007			   BSD
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