/*
 * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 * Derived (i.e. mostly copied) from arch/i386/kernel/irq.c:
 *      Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
 */

#include "linux/cpumask.h"
#include "linux/hardirq.h"
#include "linux/interrupt.h"
#include "linux/kernel_stat.h"
#include "linux/module.h"
#include "linux/sched.h"
#include "linux/seq_file.h"
#include "linux/slab.h"
#include "as-layout.h"
#include "kern_util.h"
#include "os.h"

/*
 * This list is accessed under irq_lock, except in sigio_handler,
 * where it is safe from being modified.  IRQ handlers won't change it -
 * if an IRQ source has vanished, it will be freed by free_irqs just
 * before returning from sigio_handler.  That will process a separate
 * list of irqs to free, with its own locking, coming back here to
 * remove list elements, taking the irq_lock to do so.
 */
static struct irq_fd *active_fds = NULL;
static struct irq_fd **last_irq_ptr = &active_fds;

extern void free_irqs(void);

void sigio_handler(int sig, struct uml_pt_regs *regs)
{
        struct irq_fd *irq_fd;
        int n;

        if (smp_sigio_handler())
                return;

        while (1) {
                n = os_waiting_for_events(active_fds);
                if (n <= 0) {
                        if (n == -EINTR)
                                continue;
                        else break;
                }

                for (irq_fd = active_fds; irq_fd != NULL;
                     irq_fd = irq_fd->next) {
                        if (irq_fd->current_events != 0) {
                                irq_fd->current_events = 0;
                                do_IRQ(irq_fd->irq, regs);
                        }
                }
        }

        free_irqs();
}

static DEFINE_SPINLOCK(irq_lock);

static int activate_fd(int irq, int fd, int type, void *dev_id)
{
        struct pollfd *tmp_pfd;
        struct irq_fd *new_fd, *irq_fd;
        unsigned long flags;
        int events, err, n;

        err = os_set_fd_async(fd);
        if (err < 0)
                goto out;

        err = -ENOMEM;
        new_fd = kmalloc(sizeof(struct irq_fd), GFP_KERNEL);
        if (new_fd == NULL)
                goto out;

        if (type == IRQ_READ)
                events = UM_POLLIN | UM_POLLPRI;
        else events = UM_POLLOUT;
        *new_fd = ((struct irq_fd) { .next              = NULL,
                                     .id                = dev_id,
                                     .fd                = fd,
                                     .type              = type,
                                     .irq               = irq,
                                     .events            = events,
                                     .current_events    = 0 } );

        err = -EBUSY;
        spin_lock_irqsave(&irq_lock, flags);
        for (irq_fd = active_fds; irq_fd != NULL; irq_fd = irq_fd->next) {
                if ((irq_fd->fd == fd) && (irq_fd->type == type)) {
                        printk(KERN_ERR "Registering fd %d twice\n", fd);
                        printk(KERN_ERR "Irqs : %d, %d\n", irq_fd->irq, irq);
                        printk(KERN_ERR "Ids : 0x%p, 0x%p\n", irq_fd->id,
                               dev_id);
                        goto out_unlock;
                }
        }

        if (type == IRQ_WRITE)
                fd = -1;

        tmp_pfd = NULL;
        n = 0;

        while (1) {
                n = os_create_pollfd(fd, events, tmp_pfd, n);
                if (n == 0)
                        break;

                /*
                 * n > 0
                 * It means we couldn't put new pollfd to current pollfds
                 * and tmp_fds is NULL or too small for new pollfds array.
                 * Needed size is equal to n as minimum.
                 *
                 * Here we have to drop the lock in order to call
                 * kmalloc, which might sleep.
                 * If something else came in and changed the pollfds array
                 * so we will not be able to put new pollfd struct to pollfds
                 * then we free the buffer tmp_fds and try again.
                 */
                spin_unlock_irqrestore(&irq_lock, flags);
                kfree(tmp_pfd);

                tmp_pfd = kmalloc(n, GFP_KERNEL);
                if (tmp_pfd == NULL)
                        goto out_kfree;

                spin_lock_irqsave(&irq_lock, flags);
        }

        *last_irq_ptr = new_fd;
        last_irq_ptr = &new_fd->next;

        spin_unlock_irqrestore(&irq_lock, flags);

        /*
         * This calls activate_fd, so it has to be outside the critical
         * section.
         */
        maybe_sigio_broken(fd, (type == IRQ_READ));

        return 0;

 out_unlock:
        spin_unlock_irqrestore(&irq_lock, flags);
 out_kfree:
        kfree(new_fd);
 out:
        return err;
}

static void free_irq_by_cb(int (*test)(struct irq_fd *, void *), void *arg)
{
        unsigned long flags;

        spin_lock_irqsave(&irq_lock, flags);
        os_free_irq_by_cb(test, arg, active_fds, &last_irq_ptr);
        spin_unlock_irqrestore(&irq_lock, flags);
}

struct irq_and_dev {
        int irq;
        void *dev;
};

static int same_irq_and_dev(struct irq_fd *irq, void *d)
{
        struct irq_and_dev *data = d;

        return ((irq->irq == data->irq) && (irq->id == data->dev));
}

static void free_irq_by_irq_and_dev(unsigned int irq, void *dev)
{
        struct irq_and_dev data = ((struct irq_and_dev) { .irq  = irq,
                                                          .dev  = dev });

        free_irq_by_cb(same_irq_and_dev, &data);
}

static int same_fd(struct irq_fd *irq, void *fd)
{
        return (irq->fd == *((int *)fd));
}

void free_irq_by_fd(int fd)
{
        free_irq_by_cb(same_fd, &fd);
}

/* Must be called with irq_lock held */
static struct irq_fd *find_irq_by_fd(int fd, int irqnum, int *index_out)
{
        struct irq_fd *irq;
        int i = 0;
        int fdi;

        for (irq = active_fds; irq != NULL; irq = irq->next) {
                if ((irq->fd == fd) && (irq->irq == irqnum))
                        break;
                i++;
        }
        if (irq == NULL) {
                printk(KERN_ERR "find_irq_by_fd doesn't have descriptor %d\n",
                       fd);
                goto out;
        }
        fdi = os_get_pollfd(i);
        if ((fdi != -1) && (fdi != fd)) {
                printk(KERN_ERR "find_irq_by_fd - mismatch between active_fds "
                       "and pollfds, fd %d vs %d, need %d\n", irq->fd,
                       fdi, fd);
                irq = NULL;
                goto out;
        }
        *index_out = i;
 out:
        return irq;
}

void reactivate_fd(int fd, int irqnum)
{
        struct irq_fd *irq;
        unsigned long flags;
        int i;

        spin_lock_irqsave(&irq_lock, flags);
        irq = find_irq_by_fd(fd, irqnum, &i);
        if (irq == NULL) {
                spin_unlock_irqrestore(&irq_lock, flags);
                return;
        }
        os_set_pollfd(i, irq->fd);
        spin_unlock_irqrestore(&irq_lock, flags);

        add_sigio_fd(fd);
}

void deactivate_fd(int fd, int irqnum)
{
        struct irq_fd *irq;
        unsigned long flags;
        int i;

        spin_lock_irqsave(&irq_lock, flags);
        irq = find_irq_by_fd(fd, irqnum, &i);
        if (irq == NULL) {
                spin_unlock_irqrestore(&irq_lock, flags);
                return;
        }

        os_set_pollfd(i, -1);
        spin_unlock_irqrestore(&irq_lock, flags);

        ignore_sigio_fd(fd);
}
EXPORT_SYMBOL(deactivate_fd);

/*
 * Called just before shutdown in order to provide a clean exec
 * environment in case the system is rebooting.  No locking because
 * that would cause a pointless shutdown hang if something hadn't
 * released the lock.
 */
int deactivate_all_fds(void)
{
        struct irq_fd *irq;
        int err;

        for (irq = active_fds; irq != NULL; irq = irq->next) {
                err = os_clear_fd_async(irq->fd);
                if (err)
                        return err;
        }
        /* If there is a signal already queued, after unblocking ignore it */
        os_set_ioignore();

        return 0;
}

/*
 * do_IRQ handles all normal device IRQs (the special
 * SMP cross-CPU interrupts have their own specific
 * handlers).
 */
unsigned int do_IRQ(int irq, struct uml_pt_regs *regs)
{
        struct pt_regs *old_regs = set_irq_regs((struct pt_regs *)regs);
        irq_enter();
        generic_handle_irq(irq);
        irq_exit();
        set_irq_regs(old_regs);
        return 1;
}

int um_request_irq(unsigned int irq, int fd, int type,
                   irq_handler_t handler,
                   unsigned long irqflags, const char * devname,
                   void *dev_id)
{
        int err;

        if (fd != -1) {
                err = activate_fd(irq, fd, type, dev_id);
                if (err)
                        return err;
        }

        return request_irq(irq, handler, irqflags, devname, dev_id);
}

EXPORT_SYMBOL(um_request_irq);
EXPORT_SYMBOL(reactivate_fd);

/*
 * irq_chip must define at least enable/disable and ack when
 * the edge handler is used.
 */
static void dummy(struct irq_data *d)
{
}

/* This is used for everything else than the timer. */
static struct irq_chip normal_irq_type = {
        .name = "SIGIO",
        .release = free_irq_by_irq_and_dev,
        .irq_disable = dummy,
        .irq_enable = dummy,
        .irq_ack = dummy,
};

static struct irq_chip SIGVTALRM_irq_type = {
        .name = "SIGVTALRM",
        .release = free_irq_by_irq_and_dev,
        .irq_disable = dummy,
        .irq_enable = dummy,
        .irq_ack = dummy,
};

void __init init_IRQ(void)
{
        int i;

        irq_set_chip_and_handler(TIMER_IRQ, &SIGVTALRM_irq_type, handle_edge_irq);

        for (i = 1; i < NR_IRQS; i++)
                irq_set_chip_and_handler(i, &normal_irq_type, handle_edge_irq);
}

/*
 * IRQ stack entry and exit:
 *
 * Unlike i386, UML doesn't receive IRQs on the normal kernel stack
 * and switch over to the IRQ stack after some preparation.  We use
 * sigaltstack to receive signals on a separate stack from the start.
 * These two functions make sure the rest of the kernel won't be too
 * upset by being on a different stack.  The IRQ stack has a
 * thread_info structure at the bottom so that current et al continue
 * to work.
 *
 * to_irq_stack copies the current task's thread_info to the IRQ stack
 * thread_info and sets the tasks's stack to point to the IRQ stack.
 *
 * from_irq_stack copies the thread_info struct back (flags may have
 * been modified) and resets the task's stack pointer.
 *
 * Tricky bits -
 *
 * What happens when two signals race each other?  UML doesn't block
 * signals with sigprocmask, SA_DEFER, or sa_mask, so a second signal
 * could arrive while a previous one is still setting up the
 * thread_info.
 *
 * There are three cases -
 *     The first interrupt on the stack - sets up the thread_info and
 * handles the interrupt
 *     A nested interrupt interrupting the copying of the thread_info -
 * can't handle the interrupt, as the stack is in an unknown state
 *     A nested interrupt not interrupting the copying of the
 * thread_info - doesn't do any setup, just handles the interrupt
 *
 * The first job is to figure out whether we interrupted stack setup.
 * This is done by xchging the signal mask with thread_info->pending.
 * If the value that comes back is zero, then there is no setup in
 * progress, and the interrupt can be handled.  If the value is
 * non-zero, then there is stack setup in progress.  In order to have
 * the interrupt handled, we leave our signal in the mask, and it will
 * be handled by the upper handler after it has set up the stack.
 *
 * Next is to figure out whether we are the outer handler or a nested
 * one.  As part of setting up the stack, thread_info->real_thread is
 * set to non-NULL (and is reset to NULL on exit).  This is the
 * nesting indicator.  If it is non-NULL, then the stack is already
 * set up and the handler can run.
 */

static unsigned long pending_mask;

unsigned long to_irq_stack(unsigned long *mask_out)
{
        struct thread_info *ti;
        unsigned long mask, old;
        int nested;

        mask = xchg(&pending_mask, *mask_out);
        if (mask != 0) {
                /*
                 * If any interrupts come in at this point, we want to
                 * make sure that their bits aren't lost by our
                 * putting our bit in.  So, this loop accumulates bits
                 * until xchg returns the same value that we put in.
                 * When that happens, there were no new interrupts,
                 * and pending_mask contains a bit for each interrupt
                 * that came in.
                 */
                old = *mask_out;
                do {
                        old |= mask;
                        mask = xchg(&pending_mask, old);
                } while (mask != old);
                return 1;
        }

        ti = current_thread_info();
        nested = (ti->real_thread != NULL);
        if (!nested) {
                struct task_struct *task;
                struct thread_info *tti;

                task = cpu_tasks[ti->cpu].task;
                tti = task_thread_info(task);

                *ti = *tti;
                ti->real_thread = tti;
                task->stack = ti;
        }

        mask = xchg(&pending_mask, 0);
        *mask_out |= mask | nested;
        return 0;
}

unsigned long from_irq_stack(int nested)
{
        struct thread_info *ti, *to;
        unsigned long mask;

        ti = current_thread_info();

        pending_mask = 1;

        to = ti->real_thread;
        current->stack = to;
        ti->real_thread = NULL;
        *to = *ti;

        mask = xchg(&pending_mask, 0);
        return mask & ~1;
}