/*
 * Copyright (C) 2017 - Cambridge Greys Ltd
 * Copyright (C) 2011 - 2014 Cisco Systems Inc
 * 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>
#include <irq_user.h>


/* When epoll triggers we do not know why it did so
 * we can also have different IRQs for read and write.
 * This is why we keep a small irq_fd array for each fd -
 * one entry per IRQ type
 */

struct irq_entry {
        struct irq_entry *next;
        int fd;
        struct irq_fd *irq_array[MAX_IRQ_TYPE + 1];
};

static struct irq_entry *active_fds;

static DEFINE_SPINLOCK(irq_lock);

static void irq_io_loop(struct irq_fd *irq, struct uml_pt_regs *regs)
{
/*
 * irq->active guards against reentry
 * irq->pending accumulates pending requests
 * if pending is raised the irq_handler is re-run
 * until pending is cleared
 */
        if (irq->active) {
                irq->active = false;
                do {
                        irq->pending = false;
                        do_IRQ(irq->irq, regs);
                } while (irq->pending && (!irq->purge));
                if (!irq->purge)
                        irq->active = true;
        } else {
                irq->pending = true;
        }
}

void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
{
        struct irq_entry *irq_entry;
        struct irq_fd *irq;

        int n, i, j;

        while (1) {
                /* This is now lockless - epoll keeps back-referencesto the irqs
                 * which have trigger it so there is no need to walk the irq
                 * list and lock it every time. We avoid locking by turning off
                 * IO for a specific fd by executing os_del_epoll_fd(fd) before
                 * we do any changes to the actual data structures
                 */
                n = os_waiting_for_events_epoll();

                if (n <= 0) {
                        if (n == -EINTR)
                                continue;
                        else
                                break;
                }

                for (i = 0; i < n ; i++) {
                        /* Epoll back reference is the entry with 3 irq_fd
                         * leaves - one for each irq type.
                         */
                        irq_entry = (struct irq_entry *)
                                os_epoll_get_data_pointer(i);
                        for (j = 0; j < MAX_IRQ_TYPE ; j++) {
                                irq = irq_entry->irq_array[j];
                                if (irq == NULL)
                                        continue;
                                if (os_epoll_triggered(i, irq->events) > 0)
                                        irq_io_loop(irq, regs);
                                if (irq->purge) {
                                        irq_entry->irq_array[j] = NULL;
                                        kfree(irq);
                                }
                        }
                }
        }
}

static int assign_epoll_events_to_irq(struct irq_entry *irq_entry)
{
        int i;
        int events = 0;
        struct irq_fd *irq;

        for (i = 0; i < MAX_IRQ_TYPE ; i++) {
                irq = irq_entry->irq_array[i];
                if (irq != NULL)
                        events = irq->events | events;
        }
        if (events > 0) {
        /* os_add_epoll will call os_mod_epoll if this already exists */
                return os_add_epoll_fd(events, irq_entry->fd, irq_entry);
        }
        /* No events - delete */
        return os_del_epoll_fd(irq_entry->fd);
}



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

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

        spin_lock_irqsave(&irq_lock, flags);

        /* Check if we have an entry for this fd */

        err = -EBUSY;
        for (irq_entry = active_fds;
                irq_entry != NULL; irq_entry = irq_entry->next) {
                if (irq_entry->fd == fd)
                        break;
        }

        if (irq_entry == NULL) {
                /* This needs to be atomic as it may be called from an
                 * IRQ context.
                 */
                irq_entry = kmalloc(sizeof(struct irq_entry), GFP_ATOMIC);
                if (irq_entry == NULL) {
                        printk(KERN_ERR
                                "Failed to allocate new IRQ entry\n");
                        goto out_unlock;
                }
                irq_entry->fd = fd;
                for (i = 0; i < MAX_IRQ_TYPE; i++)
                        irq_entry->irq_array[i] = NULL;
                irq_entry->next = active_fds;
                active_fds = irq_entry;
        }

        /* Check if we are trying to re-register an interrupt for a
         * particular fd
         */

        if (irq_entry->irq_array[type] != NULL) {
                printk(KERN_ERR
                        "Trying to reregister IRQ %d FD %d TYPE %d ID %p\n",
                        irq, fd, type, dev_id
                );
                goto out_unlock;
        } else {
                /* New entry for this fd */

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

                events = os_event_mask(type);

                *new_fd = ((struct irq_fd) {
                        .id             = dev_id,
                        .irq            = irq,
                        .type           = type,
                        .events         = events,
                        .active         = true,
                        .pending        = false,
                        .purge          = false
                });
                /* Turn off any IO on this fd - allows us to
                 * avoid locking the IRQ loop
                 */
                os_del_epoll_fd(irq_entry->fd);
                irq_entry->irq_array[type] = new_fd;
        }

        /* Turn back IO on with the correct (new) IO event mask */
        assign_epoll_events_to_irq(irq_entry);
        spin_unlock_irqrestore(&irq_lock, flags);
        maybe_sigio_broken(fd, (type != IRQ_NONE));

        return 0;
out_unlock:
        spin_unlock_irqrestore(&irq_lock, flags);
out:
        return err;
}

/*
 * Walk the IRQ list and dispose of any unused entries.
 * Should be done under irq_lock.
 */

static void garbage_collect_irq_entries(void)
{
        int i;
        bool reap;
        struct irq_entry *walk;
        struct irq_entry *previous = NULL;
        struct irq_entry *to_free;

        if (active_fds == NULL)
                return;
        walk = active_fds;
        while (walk != NULL) {
                reap = true;
                for (i = 0; i < MAX_IRQ_TYPE ; i++) {
                        if (walk->irq_array[i] != NULL) {
                                reap = false;
                                break;
                        }
                }
                if (reap) {
                        if (previous == NULL)
                                active_fds = walk->next;
                        else
                                previous->next = walk->next;
                        to_free = walk;
                } else {
                        to_free = NULL;
                }
                walk = walk->next;
                if (to_free != NULL)
                        kfree(to_free);
        }
}

/*
 * Walk the IRQ list and get the descriptor for our FD
 */

static struct irq_entry *get_irq_entry_by_fd(int fd)
{
        struct irq_entry *walk = active_fds;

        while (walk != NULL) {
                if (walk->fd == fd)
                        return walk;
                walk = walk->next;
        }
        return NULL;
}


/*
 * Walk the IRQ list and dispose of an entry for a specific
 * device, fd and number. Note - if sharing an IRQ for read
 * and writefor the same FD it will be disposed in either case.
 * If this behaviour is undesirable use different IRQ ids.
 */

#define IGNORE_IRQ 1
#define IGNORE_DEV (1<<1)

static void do_free_by_irq_and_dev(
        struct irq_entry *irq_entry,
        unsigned int irq,
        void *dev,
        int flags
)
{
        int i;
        struct irq_fd *to_free;

        for (i = 0; i < MAX_IRQ_TYPE ; i++) {
                if (irq_entry->irq_array[i] != NULL) {
                        if (
                        ((flags & IGNORE_IRQ) ||
                                (irq_entry->irq_array[i]->irq == irq)) &&
                        ((flags & IGNORE_DEV) ||
                                (irq_entry->irq_array[i]->id == dev))
                        ) {
                                /* Turn off any IO on this fd - allows us to
                                 * avoid locking the IRQ loop
                                 */
                                os_del_epoll_fd(irq_entry->fd);
                                to_free = irq_entry->irq_array[i];
                                irq_entry->irq_array[i] = NULL;
                                assign_epoll_events_to_irq(irq_entry);
                                if (to_free->active)
                                        to_free->purge = true;
                                else
                                        kfree(to_free);
                        }
                }
        }
}

void free_irq_by_fd(int fd)
{
        struct irq_entry *to_free;
        unsigned long flags;

        spin_lock_irqsave(&irq_lock, flags);
        to_free = get_irq_entry_by_fd(fd);
        if (to_free != NULL) {
                do_free_by_irq_and_dev(
                        to_free,
                        -1,
                        NULL,
                        IGNORE_IRQ | IGNORE_DEV
                );
        }
        garbage_collect_irq_entries();
        spin_unlock_irqrestore(&irq_lock, flags);
}
EXPORT_SYMBOL(free_irq_by_fd);

static void free_irq_by_irq_and_dev(unsigned int irq, void *dev)
{
        struct irq_entry *to_free;
        unsigned long flags;

        spin_lock_irqsave(&irq_lock, flags);
        to_free = active_fds;
        while (to_free != NULL) {
                do_free_by_irq_and_dev(
                        to_free,
                        irq,
                        dev,
                        0
                );
                to_free = to_free->next;
        }
        garbage_collect_irq_entries();
        spin_unlock_irqrestore(&irq_lock, flags);
}


void reactivate_fd(int fd, int irqnum)
{
        /** NOP - we do auto-EOI now **/
}

void deactivate_fd(int fd, int irqnum)
{
        struct irq_entry *to_free;
        unsigned long flags;

        os_del_epoll_fd(fd);
        spin_lock_irqsave(&irq_lock, flags);
        to_free = get_irq_entry_by_fd(fd);
        if (to_free != NULL) {
                do_free_by_irq_and_dev(
                        to_free,
                        irqnum,
                        NULL,
                        IGNORE_DEV
                );
        }
        garbage_collect_irq_entries();
        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)
{
        unsigned long flags;
        struct irq_entry *to_free;

        spin_lock_irqsave(&irq_lock, flags);
        /* Stop IO. The IRQ loop has no lock so this is our
         * only way of making sure we are safe to dispose
         * of all IRQ handlers
         */
        os_set_ioignore();
        to_free = active_fds;
        while (to_free != NULL) {
                do_free_by_irq_and_dev(
                        to_free,
                        -1,
                        NULL,
                        IGNORE_IRQ | IGNORE_DEV
                );
                to_free = to_free->next;
        }
        garbage_collect_irq_entries();
        spin_unlock_irqrestore(&irq_lock, flags);
        os_close_epoll_fd();
        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;
}

void um_free_irq(unsigned int irq, void *dev)
{
        free_irq_by_irq_and_dev(irq, dev);
        free_irq(irq, dev);
}
EXPORT_SYMBOL(um_free_irq);

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",
        .irq_disable = dummy,
        .irq_enable = dummy,
        .irq_ack = dummy,
        .irq_mask = dummy,
        .irq_unmask = dummy,
};

static struct irq_chip SIGVTALRM_irq_type = {
        .name = "SIGVTALRM",
        .irq_disable = dummy,
        .irq_enable = dummy,
        .irq_ack = dummy,
        .irq_mask = dummy,
        .irq_unmask = 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);
        /* Initialize EPOLL Loop */
        os_setup_epoll();
}

/*
 * 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;
}