BUS_SETUP_INTR(9)

💅 BUS_SETUP_INTR(9) 🎀

okay bestie, welcome to the Kernel Developer's Manual entry for BUS_SETUP_INTR(9) — this is the whole create/attach/teardown interrupt-handler saga, and yes it's giving main character kernel energy 💖

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✨ NAME ✨

BUS_SETUP_INTR, bus_setup_intr, BUS_TEARDOWN_INTR, bus_teardown_intr — the little friend group that creates, attaches and tears down an interrupt handler. periodt 🫶

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🌈 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);

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🌸 DESCRIPTION 🌸

The BUS_SETUP_INTR() method creates and attaches an interrupt handler to an interrupt that was previously allocated by the resource manager's BUS_ALLOC_RESOURCE(9) method. slay, but make it resource-managed 💅

The flags are found in <sys/bus.h>, and they give the broad category of interrupt. The flags also tell the interrupt handlers about certain device driver characteristics. Here's the flag lore:

• INTR_EXCL — marks the handler as being an exclusive handler for this interrupt. no sharing, bestie 🙈
• 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 that will not execute any potentially blocking operation, use the filter argument. See the “Filter Routines” section below for info 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 info on writing an interrupt handler.

The cookiep argument is a pointer to a void * that BUS_SETUP_INTR() will write a cookie into for the parent bus' use 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. iconic cleanup behavior, honestly ✨

⚠️ Mutexes are not allowed to be held across calls to these functions. like, do not do it. fr fr.

🦋 Filter Routines 🦋

A filter runs in primary interrupt context. 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.

In that restricted little environment, these are the allowed little treats:

• 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. highkey a glow-up for your locking situation 💅

🚨 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. no cap, keep it light in there 🦋

😴 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. it's giving “voluntarily surrendering the aux” 😭💀

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🎀 RETURN VALUES 🎀

Zero is returned on success, otherwise an appropriate error is returned. simple as that, bestie ✨

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👑 SEE ALSO 👑

• random(4)
• device(9)
• driver(9)
• locking(9)

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💖 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>. absolute legends, we stan 🫶

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and that's the page, bestie — footer flavor: source/version says Debian, dated November 3, 2010, under the BUS_SETUP_INTR(9) name 💋✨