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〉.