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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 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 interrupt 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
     argument.  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 handler.

     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
     establishing 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
     (specified 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
     generally cheaper to take an extra interrupt, for example, than to
     protect variables with spinlocks.  Read, modify, write cycles of hardware
     registers 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
     different 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
     minimize 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〉.