rt2x00: Simplify rt2x00_check_rev

[linux/fpc-iii.git] / kernel / irq / manage.c

/*
 * linux/kernel/irq/manage.c
 *
 * Copyright (C) 1992, 1998-2006 Linus Torvalds, Ingo Molnar
 * Copyright (C) 2005-2006 Thomas Gleixner
 *
 * This file contains driver APIs to the irq subsystem.
 */

#include <linux/irq.h>
#include <linux/kthread.h>
#include <linux/module.h>
#include <linux/random.h>
#include <linux/interrupt.h>
#include <linux/slab.h>
#include <linux/sched.h>

#include "internals.h"

/**
 *      synchronize_irq - wait for pending IRQ handlers (on other CPUs)
 *      @irq: interrupt number to wait for
 *
 *      This function waits for any pending IRQ handlers for this interrupt
 *      to complete before returning. If you use this function while
 *      holding a resource the IRQ handler may need you will deadlock.
 *
 *      This function may be called - with care - from IRQ context.
 */
void synchronize_irq(unsigned int irq)
{
        struct irq_desc *desc = irq_to_desc(irq);
        unsigned int status;

        if (!desc)
                return;

        do {
                unsigned long flags;

                /*
                 * Wait until we're out of the critical section.  This might
                 * give the wrong answer due to the lack of memory barriers.
                 */
                while (desc->status & IRQ_INPROGRESS)
                        cpu_relax();

                /* Ok, that indicated we're done: double-check carefully. */
                spin_lock_irqsave(&desc->lock, flags);
                status = desc->status;
                spin_unlock_irqrestore(&desc->lock, flags);

                /* Oops, that failed? */
        } while (status & IRQ_INPROGRESS);

        /*
         * We made sure that no hardirq handler is running. Now verify
         * that no threaded handlers are active.
         */
        wait_event(desc->wait_for_threads, !atomic_read(&desc->threads_active));
}
EXPORT_SYMBOL(synchronize_irq);

#ifdef CONFIG_SMP
cpumask_var_t irq_default_affinity;

/**
 *      irq_can_set_affinity - Check if the affinity of a given irq can be set
 *      @irq:           Interrupt to check
 *
 */
int irq_can_set_affinity(unsigned int irq)
{
        struct irq_desc *desc = irq_to_desc(irq);

        if (CHECK_IRQ_PER_CPU(desc->status) || !desc->chip ||
            !desc->chip->set_affinity)
                return 0;

        return 1;
}

static void
irq_set_thread_affinity(struct irq_desc *desc, const struct cpumask *cpumask)
{
        struct irqaction *action = desc->action;

        while (action) {
                if (action->thread)
                        set_cpus_allowed_ptr(action->thread, cpumask);
                action = action->next;
        }
}

/**
 *      irq_set_affinity - Set the irq affinity of a given irq
 *      @irq:           Interrupt to set affinity
 *      @cpumask:       cpumask
 *
 */
int irq_set_affinity(unsigned int irq, const struct cpumask *cpumask)
{
        struct irq_desc *desc = irq_to_desc(irq);
        unsigned long flags;

        if (!desc->chip->set_affinity)
                return -EINVAL;

        spin_lock_irqsave(&desc->lock, flags);

#ifdef CONFIG_GENERIC_PENDING_IRQ
        if (desc->status & IRQ_MOVE_PCNTXT || desc->status & IRQ_DISABLED) {
                cpumask_copy(desc->affinity, cpumask);
                desc->chip->set_affinity(irq, cpumask);
        } else {
                desc->status |= IRQ_MOVE_PENDING;
                cpumask_copy(desc->pending_mask, cpumask);
        }
#else
        cpumask_copy(desc->affinity, cpumask);
        desc->chip->set_affinity(irq, cpumask);
#endif
        irq_set_thread_affinity(desc, cpumask);
        desc->status |= IRQ_AFFINITY_SET;
        spin_unlock_irqrestore(&desc->lock, flags);
        return 0;
}

#ifndef CONFIG_AUTO_IRQ_AFFINITY
/*
 * Generic version of the affinity autoselector.
 */
static int setup_affinity(unsigned int irq, struct irq_desc *desc)
{
        if (!irq_can_set_affinity(irq))
                return 0;

        /*
         * Preserve an userspace affinity setup, but make sure that
         * one of the targets is online.
         */
        if (desc->status & (IRQ_AFFINITY_SET | IRQ_NO_BALANCING)) {
                if (cpumask_any_and(desc->affinity, cpu_online_mask)
                    < nr_cpu_ids)
                        goto set_affinity;
                else
                        desc->status &= ~IRQ_AFFINITY_SET;
        }

        cpumask_and(desc->affinity, cpu_online_mask, irq_default_affinity);
set_affinity:
        desc->chip->set_affinity(irq, desc->affinity);

        return 0;
}
#else
static inline int setup_affinity(unsigned int irq, struct irq_desc *d)
{
        return irq_select_affinity(irq);
}
#endif

/*
 * Called when affinity is set via /proc/irq
 */
int irq_select_affinity_usr(unsigned int irq)
{
        struct irq_desc *desc = irq_to_desc(irq);
        unsigned long flags;
        int ret;

        spin_lock_irqsave(&desc->lock, flags);
        ret = setup_affinity(irq, desc);
        if (!ret)
                irq_set_thread_affinity(desc, desc->affinity);
        spin_unlock_irqrestore(&desc->lock, flags);

        return ret;
}

#else
static inline int setup_affinity(unsigned int irq, struct irq_desc *desc)
{
        return 0;
}
#endif

void __disable_irq(struct irq_desc *desc, unsigned int irq, bool suspend)
{
        if (suspend) {
                if (!desc->action || (desc->action->flags & IRQF_TIMER))
                        return;
                desc->status |= IRQ_SUSPENDED;
        }

        if (!desc->depth++) {
                desc->status |= IRQ_DISABLED;
                desc->chip->disable(irq);
        }
}

/**
 *      disable_irq_nosync - disable an irq without waiting
 *      @irq: Interrupt to disable
 *
 *      Disable the selected interrupt line.  Disables and Enables are
 *      nested.
 *      Unlike disable_irq(), this function does not ensure existing
 *      instances of the IRQ handler have completed before returning.
 *
 *      This function may be called from IRQ context.
 */
void disable_irq_nosync(unsigned int irq)
{
        struct irq_desc *desc = irq_to_desc(irq);
        unsigned long flags;

        if (!desc)
                return;

        spin_lock_irqsave(&desc->lock, flags);
        __disable_irq(desc, irq, false);
        spin_unlock_irqrestore(&desc->lock, flags);
}
EXPORT_SYMBOL(disable_irq_nosync);

/**
 *      disable_irq - disable an irq and wait for completion
 *      @irq: Interrupt to disable
 *
 *      Disable the selected interrupt line.  Enables and Disables are
 *      nested.
 *      This function waits for any pending IRQ handlers for this interrupt
 *      to complete before returning. If you use this function while
 *      holding a resource the IRQ handler may need you will deadlock.
 *
 *      This function may be called - with care - from IRQ context.
 */
void disable_irq(unsigned int irq)
{
        struct irq_desc *desc = irq_to_desc(irq);

        if (!desc)
                return;

        disable_irq_nosync(irq);
        if (desc->action)
                synchronize_irq(irq);
}
EXPORT_SYMBOL(disable_irq);

void __enable_irq(struct irq_desc *desc, unsigned int irq, bool resume)
{
        if (resume)
                desc->status &= ~IRQ_SUSPENDED;

        switch (desc->depth) {
        case 0:
 err_out:
                WARN(1, KERN_WARNING "Unbalanced enable for IRQ %d\n", irq);
                break;
        case 1: {
                unsigned int status = desc->status & ~IRQ_DISABLED;

                if (desc->status & IRQ_SUSPENDED)
                        goto err_out;
                /* Prevent probing on this irq: */
                desc->status = status | IRQ_NOPROBE;
                check_irq_resend(desc, irq);
                /* fall-through */
        }
        default:
                desc->depth--;
        }
}

/**
 *      enable_irq - enable handling of an irq
 *      @irq: Interrupt to enable
 *
 *      Undoes the effect of one call to disable_irq().  If this
 *      matches the last disable, processing of interrupts on this
 *      IRQ line is re-enabled.
 *
 *      This function may be called from IRQ context.
 */
void enable_irq(unsigned int irq)
{
        struct irq_desc *desc = irq_to_desc(irq);
        unsigned long flags;

        if (!desc)
                return;

        spin_lock_irqsave(&desc->lock, flags);
        __enable_irq(desc, irq, false);
        spin_unlock_irqrestore(&desc->lock, flags);
}
EXPORT_SYMBOL(enable_irq);

static int set_irq_wake_real(unsigned int irq, unsigned int on)
{
        struct irq_desc *desc = irq_to_desc(irq);
        int ret = -ENXIO;

        if (desc->chip->set_wake)
                ret = desc->chip->set_wake(irq, on);

        return ret;
}

/**
 *      set_irq_wake - control irq power management wakeup
 *      @irq:   interrupt to control
 *      @on:    enable/disable power management wakeup
 *
 *      Enable/disable power management wakeup mode, which is
 *      disabled by default.  Enables and disables must match,
 *      just as they match for non-wakeup mode support.
 *
 *      Wakeup mode lets this IRQ wake the system from sleep
 *      states like "suspend to RAM".
 */
int set_irq_wake(unsigned int irq, unsigned int on)
{
        struct irq_desc *desc = irq_to_desc(irq);
        unsigned long flags;
        int ret = 0;

        /* wakeup-capable irqs can be shared between drivers that
         * don't need to have the same sleep mode behaviors.
         */
        spin_lock_irqsave(&desc->lock, flags);
        if (on) {
                if (desc->wake_depth++ == 0) {
                        ret = set_irq_wake_real(irq, on);
                        if (ret)
                                desc->wake_depth = 0;
                        else
                                desc->status |= IRQ_WAKEUP;
                }
        } else {
                if (desc->wake_depth == 0) {
                        WARN(1, "Unbalanced IRQ %d wake disable\n", irq);
                } else if (--desc->wake_depth == 0) {
                        ret = set_irq_wake_real(irq, on);
                        if (ret)
                                desc->wake_depth = 1;
                        else
                                desc->status &= ~IRQ_WAKEUP;
                }
        }

        spin_unlock_irqrestore(&desc->lock, flags);
        return ret;
}
EXPORT_SYMBOL(set_irq_wake);

/*
 * Internal function that tells the architecture code whether a
 * particular irq has been exclusively allocated or is available
 * for driver use.
 */
int can_request_irq(unsigned int irq, unsigned long irqflags)
{
        struct irq_desc *desc = irq_to_desc(irq);
        struct irqaction *action;

        if (!desc)
                return 0;

        if (desc->status & IRQ_NOREQUEST)
                return 0;

        action = desc->action;
        if (action)
                if (irqflags & action->flags & IRQF_SHARED)
                        action = NULL;

        return !action;
}

void compat_irq_chip_set_default_handler(struct irq_desc *desc)
{
        /*
         * If the architecture still has not overriden
         * the flow handler then zap the default. This
         * should catch incorrect flow-type setting.
         */
        if (desc->handle_irq == &handle_bad_irq)
                desc->handle_irq = NULL;
}

int __irq_set_trigger(struct irq_desc *desc, unsigned int irq,
                unsigned long flags)
{
        int ret;
        struct irq_chip *chip = desc->chip;

        if (!chip || !chip->set_type) {
                /*
                 * IRQF_TRIGGER_* but the PIC does not support multiple
                 * flow-types?
                 */
                pr_debug("No set_type function for IRQ %d (%s)\n", irq,
                                chip ? (chip->name ? : "unknown") : "unknown");
                return 0;
        }

        /* caller masked out all except trigger mode flags */
        ret = chip->set_type(irq, flags);

        if (ret)
                pr_err("setting trigger mode %d for irq %u failed (%pF)\n",
                                (int)flags, irq, chip->set_type);
        else {
                if (flags & (IRQ_TYPE_LEVEL_LOW | IRQ_TYPE_LEVEL_HIGH))
                        flags |= IRQ_LEVEL;
                /* note that IRQF_TRIGGER_MASK == IRQ_TYPE_SENSE_MASK */
                desc->status &= ~(IRQ_LEVEL | IRQ_TYPE_SENSE_MASK);
                desc->status |= flags;
        }

        return ret;
}

static int irq_wait_for_interrupt(struct irqaction *action)
{
        while (!kthread_should_stop()) {
                set_current_state(TASK_INTERRUPTIBLE);

                if (test_and_clear_bit(IRQTF_RUNTHREAD,
                                       &action->thread_flags)) {
                        __set_current_state(TASK_RUNNING);
                        return 0;
                }
                schedule();
        }
        return -1;
}

/*
 * Interrupt handler thread
 */
static int irq_thread(void *data)
{
        struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO/2, };
        struct irqaction *action = data;
        struct irq_desc *desc = irq_to_desc(action->irq);
        int wake;

        sched_setscheduler(current, SCHED_FIFO, &param);
        current->irqaction = action;

        while (!irq_wait_for_interrupt(action)) {

                atomic_inc(&desc->threads_active);

                spin_lock_irq(&desc->lock);
                if (unlikely(desc->status & IRQ_DISABLED)) {
                        /*
                         * CHECKME: We might need a dedicated
                         * IRQ_THREAD_PENDING flag here, which
                         * retriggers the thread in check_irq_resend()
                         * but AFAICT IRQ_PENDING should be fine as it
                         * retriggers the interrupt itself --- tglx
                         */
                        desc->status |= IRQ_PENDING;
                        spin_unlock_irq(&desc->lock);
                } else {
                        spin_unlock_irq(&desc->lock);

                        action->thread_fn(action->irq, action->dev_id);
                }

                wake = atomic_dec_and_test(&desc->threads_active);

                if (wake && waitqueue_active(&desc->wait_for_threads))
                        wake_up(&desc->wait_for_threads);
        }

        /*
         * Clear irqaction. Otherwise exit_irq_thread() would make
         * fuzz about an active irq thread going into nirvana.
         */
        current->irqaction = NULL;
        return 0;
}

/*
 * Called from do_exit()
 */
void exit_irq_thread(void)
{
        struct task_struct *tsk = current;

        if (!tsk->irqaction)
                return;

        printk(KERN_ERR
               "exiting task \"%s\" (%d) is an active IRQ thread (irq %d)\n",
               tsk->comm ? tsk->comm : "", tsk->pid, tsk->irqaction->irq);

        /*
         * Set the THREAD DIED flag to prevent further wakeups of the
         * soon to be gone threaded handler.
         */
        set_bit(IRQTF_DIED, &tsk->irqaction->flags);
}

/*
 * Internal function to register an irqaction - typically used to
 * allocate special interrupts that are part of the architecture.
 */
static int
__setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
{
        struct irqaction *old, **old_ptr;
        const char *old_name = NULL;
        unsigned long flags;
        int shared = 0;
        int ret;

        if (!desc)
                return -EINVAL;

        if (desc->chip == &no_irq_chip)
                return -ENOSYS;
        /*
         * Some drivers like serial.c use request_irq() heavily,
         * so we have to be careful not to interfere with a
         * running system.
         */
        if (new->flags & IRQF_SAMPLE_RANDOM) {
                /*
                 * This function might sleep, we want to call it first,
                 * outside of the atomic block.
                 * Yes, this might clear the entropy pool if the wrong
                 * driver is attempted to be loaded, without actually
                 * installing a new handler, but is this really a problem,
                 * only the sysadmin is able to do this.
                 */
                rand_initialize_irq(irq);
        }

        /*
         * Threaded handler ?
         */
        if (new->thread_fn) {
                struct task_struct *t;

                t = kthread_create(irq_thread, new, "irq/%d-%s", irq,
                                   new->name);
                if (IS_ERR(t))
                        return PTR_ERR(t);
                /*
                 * We keep the reference to the task struct even if
                 * the thread dies to avoid that the interrupt code
                 * references an already freed task_struct.
                 */
                get_task_struct(t);
                new->thread = t;
                wake_up_process(t);
        }

        /*
         * The following block of code has to be executed atomically
         */
        spin_lock_irqsave(&desc->lock, flags);
        old_ptr = &desc->action;
        old = *old_ptr;
        if (old) {
                /*
                 * Can't share interrupts unless both agree to and are
                 * the same type (level, edge, polarity). So both flag
                 * fields must have IRQF_SHARED set and the bits which
                 * set the trigger type must match.
                 */
                if (!((old->flags & new->flags) & IRQF_SHARED) ||
                    ((old->flags ^ new->flags) & IRQF_TRIGGER_MASK)) {
                        old_name = old->name;
                        goto mismatch;
                }

#if defined(CONFIG_IRQ_PER_CPU)
                /* All handlers must agree on per-cpuness */
                if ((old->flags & IRQF_PERCPU) !=
                    (new->flags & IRQF_PERCPU))
                        goto mismatch;
#endif

                /* add new interrupt at end of irq queue */
                do {
                        old_ptr = &old->next;
                        old = *old_ptr;
                } while (old);
                shared = 1;
        }

        if (!shared) {
                irq_chip_set_defaults(desc->chip);

                init_waitqueue_head(&desc->wait_for_threads);

                /* Setup the type (level, edge polarity) if configured: */
                if (new->flags & IRQF_TRIGGER_MASK) {
                        ret = __irq_set_trigger(desc, irq,
                                        new->flags & IRQF_TRIGGER_MASK);

                        if (ret)
                                goto out_thread;
                } else
                        compat_irq_chip_set_default_handler(desc);
#if defined(CONFIG_IRQ_PER_CPU)
                if (new->flags & IRQF_PERCPU)
                        desc->status |= IRQ_PER_CPU;
#endif

                desc->status &= ~(IRQ_AUTODETECT | IRQ_WAITING |
                                  IRQ_INPROGRESS | IRQ_SPURIOUS_DISABLED);

                if (!(desc->status & IRQ_NOAUTOEN)) {
                        desc->depth = 0;
                        desc->status &= ~IRQ_DISABLED;
                        desc->chip->startup(irq);
                } else
                        /* Undo nested disables: */
                        desc->depth = 1;

                /* Exclude IRQ from balancing if requested */
                if (new->flags & IRQF_NOBALANCING)
                        desc->status |= IRQ_NO_BALANCING;

                /* Set default affinity mask once everything is setup */
                setup_affinity(irq, desc);

        } else if ((new->flags & IRQF_TRIGGER_MASK)
                        && (new->flags & IRQF_TRIGGER_MASK)
                                != (desc->status & IRQ_TYPE_SENSE_MASK)) {
                /* hope the handler works with the actual trigger mode... */
                pr_warning("IRQ %d uses trigger mode %d; requested %d\n",
                                irq, (int)(desc->status & IRQ_TYPE_SENSE_MASK),
                                (int)(new->flags & IRQF_TRIGGER_MASK));
        }

        *old_ptr = new;

        /* Reset broken irq detection when installing new handler */
        desc->irq_count = 0;
        desc->irqs_unhandled = 0;

        /*
         * Check whether we disabled the irq via the spurious handler
         * before. Reenable it and give it another chance.
         */
        if (shared && (desc->status & IRQ_SPURIOUS_DISABLED)) {
                desc->status &= ~IRQ_SPURIOUS_DISABLED;
                __enable_irq(desc, irq, false);
        }

        spin_unlock_irqrestore(&desc->lock, flags);

        new->irq = irq;
        register_irq_proc(irq, desc);
        new->dir = NULL;
        register_handler_proc(irq, new);

        return 0;

mismatch:
#ifdef CONFIG_DEBUG_SHIRQ
        if (!(new->flags & IRQF_PROBE_SHARED)) {
                printk(KERN_ERR "IRQ handler type mismatch for IRQ %d\n", irq);
                if (old_name)
                        printk(KERN_ERR "current handler: %s\n", old_name);
                dump_stack();
        }
#endif
        ret = -EBUSY;

out_thread:
        spin_unlock_irqrestore(&desc->lock, flags);
        if (new->thread) {
                struct task_struct *t = new->thread;

                new->thread = NULL;
                if (likely(!test_bit(IRQTF_DIED, &new->thread_flags)))
                        kthread_stop(t);
                put_task_struct(t);
        }
        return ret;
}

/**
 *      setup_irq - setup an interrupt
 *      @irq: Interrupt line to setup
 *      @act: irqaction for the interrupt
 *
 * Used to statically setup interrupts in the early boot process.
 */
int setup_irq(unsigned int irq, struct irqaction *act)
{
        struct irq_desc *desc = irq_to_desc(irq);

        return __setup_irq(irq, desc, act);
}
EXPORT_SYMBOL_GPL(setup_irq);

 /*
 * Internal function to unregister an irqaction - used to free
 * regular and special interrupts that are part of the architecture.
 */
static struct irqaction *__free_irq(unsigned int irq, void *dev_id)
{
        struct irq_desc *desc = irq_to_desc(irq);
        struct irqaction *action, **action_ptr;
        struct task_struct *irqthread;
        unsigned long flags;

        WARN(in_interrupt(), "Trying to free IRQ %d from IRQ context!\n", irq);

        if (!desc)
                return NULL;

        spin_lock_irqsave(&desc->lock, flags);

        /*
         * There can be multiple actions per IRQ descriptor, find the right
         * one based on the dev_id:
         */
        action_ptr = &desc->action;
        for (;;) {
                action = *action_ptr;

                if (!action) {
                        WARN(1, "Trying to free already-free IRQ %d\n", irq);
                        spin_unlock_irqrestore(&desc->lock, flags);

                        return NULL;
                }

                if (action->dev_id == dev_id)
                        break;
                action_ptr = &action->next;
        }

        /* Found it - now remove it from the list of entries: */
        *action_ptr = action->next;

        /* Currently used only by UML, might disappear one day: */
#ifdef CONFIG_IRQ_RELEASE_METHOD
        if (desc->chip->release)
                desc->chip->release(irq, dev_id);
#endif

        /* If this was the last handler, shut down the IRQ line: */
        if (!desc->action) {
                desc->status |= IRQ_DISABLED;
                if (desc->chip->shutdown)
                        desc->chip->shutdown(irq);
                else
                        desc->chip->disable(irq);
        }

        irqthread = action->thread;
        action->thread = NULL;

        spin_unlock_irqrestore(&desc->lock, flags);

        unregister_handler_proc(irq, action);

        /* Make sure it's not being used on another CPU: */
        synchronize_irq(irq);

        if (irqthread) {
                if (!test_bit(IRQTF_DIED, &action->thread_flags))
                        kthread_stop(irqthread);
                put_task_struct(irqthread);
        }

#ifdef CONFIG_DEBUG_SHIRQ
        /*
         * It's a shared IRQ -- the driver ought to be prepared for an IRQ
         * event to happen even now it's being freed, so let's make sure that
         * is so by doing an extra call to the handler ....
         *
         * ( We do this after actually deregistering it, to make sure that a
         *   'real' IRQ doesn't run in * parallel with our fake. )
         */
        if (action->flags & IRQF_SHARED) {
                local_irq_save(flags);
                action->handler(irq, dev_id);
                local_irq_restore(flags);
        }
#endif
        return action;
}

/**
 *      remove_irq - free an interrupt
 *      @irq: Interrupt line to free
 *      @act: irqaction for the interrupt
 *
 * Used to remove interrupts statically setup by the early boot process.
 */
void remove_irq(unsigned int irq, struct irqaction *act)
{
        __free_irq(irq, act->dev_id);
}
EXPORT_SYMBOL_GPL(remove_irq);

/**
 *      free_irq - free an interrupt allocated with request_irq
 *      @irq: Interrupt line to free
 *      @dev_id: Device identity to free
 *
 *      Remove an interrupt handler. The handler is removed and if the
 *      interrupt line is no longer in use by any driver it is disabled.
 *      On a shared IRQ the caller must ensure the interrupt is disabled
 *      on the card it drives before calling this function. The function
 *      does not return until any executing interrupts for this IRQ
 *      have completed.
 *
 *      This function must not be called from interrupt context.
 */
void free_irq(unsigned int irq, void *dev_id)
{
        kfree(__free_irq(irq, dev_id));
}
EXPORT_SYMBOL(free_irq);

/**
 *      request_threaded_irq - allocate an interrupt line
 *      @irq: Interrupt line to allocate
 *      @handler: Function to be called when the IRQ occurs.
 *                Primary handler for threaded interrupts
 *      @thread_fn: Function called from the irq handler thread
 *                  If NULL, no irq thread is created
 *      @irqflags: Interrupt type flags
 *      @devname: An ascii name for the claiming device
 *      @dev_id: A cookie passed back to the handler function
 *
 *      This call allocates interrupt resources and enables the
 *      interrupt line and IRQ handling. From the point this
 *      call is made your handler function may be invoked. Since
 *      your handler function must clear any interrupt the board
 *      raises, you must take care both to initialise your hardware
 *      and to set up the interrupt handler in the right order.
 *
 *      If you want to set up a threaded irq handler for your device
 *      then you need to supply @handler and @thread_fn. @handler ist
 *      still called in hard interrupt context and has to check
 *      whether the interrupt originates from the device. If yes it
 *      needs to disable the interrupt on the device and return
 *      IRQ_THREAD_WAKE which will wake up the handler thread and run
 *      @thread_fn. This split handler design is necessary to support
 *      shared interrupts.
 *
 *      Dev_id must be globally unique. Normally the address of the
 *      device data structure is used as the cookie. Since the handler
 *      receives this value it makes sense to use it.
 *
 *      If your interrupt is shared you must pass a non NULL dev_id
 *      as this is required when freeing the interrupt.
 *
 *      Flags:
 *
 *      IRQF_SHARED             Interrupt is shared
 *      IRQF_DISABLED   Disable local interrupts while processing
 *      IRQF_SAMPLE_RANDOM      The interrupt can be used for entropy
 *      IRQF_TRIGGER_*          Specify active edge(s) or level
 *
 */
int request_threaded_irq(unsigned int irq, irq_handler_t handler,
                         irq_handler_t thread_fn, unsigned long irqflags,
                         const char *devname, void *dev_id)
{
        struct irqaction *action;
        struct irq_desc *desc;
        int retval;

        /*
         * handle_IRQ_event() always ignores IRQF_DISABLED except for
         * the _first_ irqaction (sigh).  That can cause oopsing, but
         * the behavior is classified as "will not fix" so we need to
         * start nudging drivers away from using that idiom.
         */
        if ((irqflags & (IRQF_SHARED|IRQF_DISABLED)) ==
                                        (IRQF_SHARED|IRQF_DISABLED)) {
                pr_warning(
                  "IRQ %d/%s: IRQF_DISABLED is not guaranteed on shared IRQs\n",
                        irq, devname);
        }

#ifdef CONFIG_LOCKDEP
        /*
         * Lockdep wants atomic interrupt handlers:
         */
        irqflags |= IRQF_DISABLED;
#endif
        /*
         * Sanity-check: shared interrupts must pass in a real dev-ID,
         * otherwise we'll have trouble later trying to figure out
         * which interrupt is which (messes up the interrupt freeing
         * logic etc).
         */
        if ((irqflags & IRQF_SHARED) && !dev_id)
                return -EINVAL;

        desc = irq_to_desc(irq);
        if (!desc)
                return -EINVAL;

        if (desc->status & IRQ_NOREQUEST)
                return -EINVAL;
        if (!handler)
                return -EINVAL;

        action = kzalloc(sizeof(struct irqaction), GFP_KERNEL);
        if (!action)
                return -ENOMEM;

        action->handler = handler;
        action->thread_fn = thread_fn;
        action->flags = irqflags;
        action->name = devname;
        action->dev_id = dev_id;

        retval = __setup_irq(irq, desc, action);
        if (retval)
                kfree(action);

#ifdef CONFIG_DEBUG_SHIRQ
        if (irqflags & IRQF_SHARED) {
                /*
                 * It's a shared IRQ -- the driver ought to be prepared for it
                 * to happen immediately, so let's make sure....
                 * We disable the irq to make sure that a 'real' IRQ doesn't
                 * run in parallel with our fake.
                 */
                unsigned long flags;

                disable_irq(irq);
                local_irq_save(flags);

                handler(irq, dev_id);

                local_irq_restore(flags);
                enable_irq(irq);
        }
#endif
        return retval;
}
EXPORT_SYMBOL(request_threaded_irq);