/*
 * Split spinlock implementation out into its own file, so it can be
 * compiled in a FTRACE-compatible way.
 */
#include <linux/kernel_stat.h>
#include <linux/spinlock.h>
#include <linux/debugfs.h>
#include <linux/log2.h>
#include <linux/gfp.h>

#include <asm/paravirt.h>

#include <xen/interface/xen.h>
#include <xen/events.h>

#include "xen-ops.h"
#include "debugfs.h"

#ifdef CONFIG_XEN_DEBUG_FS
static struct xen_spinlock_stats
{
        u64 taken;
        u32 taken_slow;
        u32 taken_slow_nested;
        u32 taken_slow_pickup;
        u32 taken_slow_spurious;
        u32 taken_slow_irqenable;

        u64 released;
        u32 released_slow;
        u32 released_slow_kicked;

#define HISTO_BUCKETS   30
        u32 histo_spin_total[HISTO_BUCKETS+1];
        u32 histo_spin_spinning[HISTO_BUCKETS+1];
        u32 histo_spin_blocked[HISTO_BUCKETS+1];

        u64 time_total;
        u64 time_spinning;
        u64 time_blocked;
} spinlock_stats;

static u8 zero_stats;

static unsigned lock_timeout = 1 << 10;
#define TIMEOUT lock_timeout

static inline void check_zero(void)
{
        if (unlikely(zero_stats)) {
                memset(&spinlock_stats, 0, sizeof(spinlock_stats));
                zero_stats = 0;
        }
}

#define ADD_STATS(elem, val)                    \
        do { check_zero(); spinlock_stats.elem += (val); } while(0)

static inline u64 spin_time_start(void)
{
        return xen_clocksource_read();
}

static void __spin_time_accum(u64 delta, u32 *array)
{
        unsigned index = ilog2(delta);

        check_zero();

        if (index < HISTO_BUCKETS)
                array[index]++;
        else
                array[HISTO_BUCKETS]++;
}

static inline void spin_time_accum_spinning(u64 start)
{
        u32 delta = xen_clocksource_read() - start;

        __spin_time_accum(delta, spinlock_stats.histo_spin_spinning);
        spinlock_stats.time_spinning += delta;
}

static inline void spin_time_accum_total(u64 start)
{
        u32 delta = xen_clocksource_read() - start;

        __spin_time_accum(delta, spinlock_stats.histo_spin_total);
        spinlock_stats.time_total += delta;
}

static inline void spin_time_accum_blocked(u64 start)
{
        u32 delta = xen_clocksource_read() - start;

        __spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
        spinlock_stats.time_blocked += delta;
}
#else  /* !CONFIG_XEN_DEBUG_FS */
#define TIMEOUT                 (1 << 10)
#define ADD_STATS(elem, val)    do { (void)(val); } while(0)

static inline u64 spin_time_start(void)
{
        return 0;
}

static inline void spin_time_accum_total(u64 start)
{
}
static inline void spin_time_accum_spinning(u64 start)
{
}
static inline void spin_time_accum_blocked(u64 start)
{
}
#endif  /* CONFIG_XEN_DEBUG_FS */

struct xen_spinlock {
        unsigned char lock;             /* 0 -> free; 1 -> locked */
        unsigned short spinners;        /* count of waiting cpus */
};

static int xen_spin_is_locked(struct arch_spinlock *lock)
{
        struct xen_spinlock *xl = (struct xen_spinlock *)lock;

        return xl->lock != 0;
}

static int xen_spin_is_contended(struct arch_spinlock *lock)
{
        struct xen_spinlock *xl = (struct xen_spinlock *)lock;

        /* Not strictly true; this is only the count of contended
           lock-takers entering the slow path. */
        return xl->spinners != 0;
}

static int xen_spin_trylock(struct arch_spinlock *lock)
{
        struct xen_spinlock *xl = (struct xen_spinlock *)lock;
        u8 old = 1;

        asm("xchgb %b0,%1"
            : "+q" (old), "+m" (xl->lock) : : "memory");

        return old == 0;
}

static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners);

/*
 * Mark a cpu as interested in a lock.  Returns the CPU's previous
 * lock of interest, in case we got preempted by an interrupt.
 */
static inline struct xen_spinlock *spinning_lock(struct xen_spinlock *xl)
{
        struct xen_spinlock *prev;

        prev = __this_cpu_read(lock_spinners);
        __this_cpu_write(lock_spinners, xl);

        wmb();                  /* set lock of interest before count */

        asm(LOCK_PREFIX " incw %0"
            : "+m" (xl->spinners) : : "memory");

        return prev;
}

/*
 * Mark a cpu as no longer interested in a lock.  Restores previous
 * lock of interest (NULL for none).
 */
static inline void unspinning_lock(struct xen_spinlock *xl, struct xen_spinlock *prev)
{
        asm(LOCK_PREFIX " decw %0"
            : "+m" (xl->spinners) : : "memory");
        wmb();                  /* decrement count before restoring lock */
        __this_cpu_write(lock_spinners, prev);
}

static noinline int xen_spin_lock_slow(struct arch_spinlock *lock, bool irq_enable)
{
        struct xen_spinlock *xl = (struct xen_spinlock *)lock;
        struct xen_spinlock *prev;
        int irq = __this_cpu_read(lock_kicker_irq);
        int ret;
        u64 start;

        /* If kicker interrupts not initialized yet, just spin */
        if (irq == -1)
                return 0;

        start = spin_time_start();

        /* announce we're spinning */
        prev = spinning_lock(xl);

        ADD_STATS(taken_slow, 1);
        ADD_STATS(taken_slow_nested, prev != NULL);

        do {
                unsigned long flags;

                /* clear pending */
                xen_clear_irq_pending(irq);

                /* check again make sure it didn't become free while
                   we weren't looking  */
                ret = xen_spin_trylock(lock);
                if (ret) {
                        ADD_STATS(taken_slow_pickup, 1);

                        /*
                         * If we interrupted another spinlock while it
                         * was blocking, make sure it doesn't block
                         * without rechecking the lock.
                         */
                        if (prev != NULL)
                                xen_set_irq_pending(irq);
                        goto out;
                }

                flags = arch_local_save_flags();
                if (irq_enable) {
                        ADD_STATS(taken_slow_irqenable, 1);
                        raw_local_irq_enable();
                }

                /*
                 * Block until irq becomes pending.  If we're
                 * interrupted at this point (after the trylock but
                 * before entering the block), then the nested lock
                 * handler guarantees that the irq will be left
                 * pending if there's any chance the lock became free;
                 * xen_poll_irq() returns immediately if the irq is
                 * pending.
                 */
                xen_poll_irq(irq);

                raw_local_irq_restore(flags);

                ADD_STATS(taken_slow_spurious, !xen_test_irq_pending(irq));
        } while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */

        kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));

out:
        unspinning_lock(xl, prev);
        spin_time_accum_blocked(start);

        return ret;
}

static inline void __xen_spin_lock(struct arch_spinlock *lock, bool irq_enable)
{
        struct xen_spinlock *xl = (struct xen_spinlock *)lock;
        unsigned timeout;
        u8 oldval;
        u64 start_spin;

        ADD_STATS(taken, 1);

        start_spin = spin_time_start();

        do {
                u64 start_spin_fast = spin_time_start();

                timeout = TIMEOUT;

                asm("1: xchgb %1,%0\n"
                    "   testb %1,%1\n"
                    "   jz 3f\n"
                    "2: rep;nop\n"
                    "   cmpb $0,%0\n"
                    "   je 1b\n"
                    "   dec %2\n"
                    "   jnz 2b\n"
                    "3:\n"
                    : "+m" (xl->lock), "=q" (oldval), "+r" (timeout)
                    : "1" (1)
                    : "memory");

                spin_time_accum_spinning(start_spin_fast);

        } while (unlikely(oldval != 0 &&
                          (TIMEOUT == ~0 || !xen_spin_lock_slow(lock, irq_enable))));

        spin_time_accum_total(start_spin);
}

static void xen_spin_lock(struct arch_spinlock *lock)
{
        __xen_spin_lock(lock, false);
}

static void xen_spin_lock_flags(struct arch_spinlock *lock, unsigned long flags)
{
        __xen_spin_lock(lock, !raw_irqs_disabled_flags(flags));
}

static noinline void xen_spin_unlock_slow(struct xen_spinlock *xl)
{
        int cpu;

        ADD_STATS(released_slow, 1);

        for_each_online_cpu(cpu) {
                /* XXX should mix up next cpu selection */
                if (per_cpu(lock_spinners, cpu) == xl) {
                        ADD_STATS(released_slow_kicked, 1);
                        xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
                        break;
                }
        }
}

static void xen_spin_unlock(struct arch_spinlock *lock)
{
        struct xen_spinlock *xl = (struct xen_spinlock *)lock;

        ADD_STATS(released, 1);

        smp_wmb();              /* make sure no writes get moved after unlock */
        xl->lock = 0;           /* release lock */

        /*
         * Make sure unlock happens before checking for waiting
         * spinners.  We need a strong barrier to enforce the
         * write-read ordering to different memory locations, as the
         * CPU makes no implied guarantees about their ordering.
         */
        mb();

        if (unlikely(xl->spinners))
                xen_spin_unlock_slow(xl);
}

static irqreturn_t dummy_handler(int irq, void *dev_id)
{
        BUG();
        return IRQ_HANDLED;
}

void __cpuinit xen_init_lock_cpu(int cpu)
{
        int irq;
        const char *name;

        name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
        irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
                                     cpu,
                                     dummy_handler,
                                     IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
                                     name,
                                     NULL);

        if (irq >= 0) {
                disable_irq(irq); /* make sure it's never delivered */
                per_cpu(lock_kicker_irq, cpu) = irq;
        }

        printk("cpu %d spinlock event irq %d\n", cpu, irq);
}

void xen_uninit_lock_cpu(int cpu)
{
        unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
}

void __init xen_init_spinlocks(void)
{
        pv_lock_ops.spin_is_locked = xen_spin_is_locked;
        pv_lock_ops.spin_is_contended = xen_spin_is_contended;
        pv_lock_ops.spin_lock = xen_spin_lock;
        pv_lock_ops.spin_lock_flags = xen_spin_lock_flags;
        pv_lock_ops.spin_trylock = xen_spin_trylock;
        pv_lock_ops.spin_unlock = xen_spin_unlock;
}

#ifdef CONFIG_XEN_DEBUG_FS

static struct dentry *d_spin_debug;

static int __init xen_spinlock_debugfs(void)
{
        struct dentry *d_xen = xen_init_debugfs();

        if (d_xen == NULL)
                return -ENOMEM;

        d_spin_debug = debugfs_create_dir("spinlocks", d_xen);

        debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);

        debugfs_create_u32("timeout", 0644, d_spin_debug, &lock_timeout);

        debugfs_create_u64("taken", 0444, d_spin_debug, &spinlock_stats.taken);
        debugfs_create_u32("taken_slow", 0444, d_spin_debug,
                           &spinlock_stats.taken_slow);
        debugfs_create_u32("taken_slow_nested", 0444, d_spin_debug,
                           &spinlock_stats.taken_slow_nested);
        debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
                           &spinlock_stats.taken_slow_pickup);
        debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
                           &spinlock_stats.taken_slow_spurious);
        debugfs_create_u32("taken_slow_irqenable", 0444, d_spin_debug,
                           &spinlock_stats.taken_slow_irqenable);

        debugfs_create_u64("released", 0444, d_spin_debug, &spinlock_stats.released);
        debugfs_create_u32("released_slow", 0444, d_spin_debug,
                           &spinlock_stats.released_slow);
        debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
                           &spinlock_stats.released_slow_kicked);

        debugfs_create_u64("time_spinning", 0444, d_spin_debug,
                           &spinlock_stats.time_spinning);
        debugfs_create_u64("time_blocked", 0444, d_spin_debug,
                           &spinlock_stats.time_blocked);
        debugfs_create_u64("time_total", 0444, d_spin_debug,
                           &spinlock_stats.time_total);

        xen_debugfs_create_u32_array("histo_total", 0444, d_spin_debug,
                                     spinlock_stats.histo_spin_total, HISTO_BUCKETS + 1);
        xen_debugfs_create_u32_array("histo_spinning", 0444, d_spin_debug,
                                     spinlock_stats.histo_spin_spinning, HISTO_BUCKETS + 1);
        xen_debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
                                     spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);

        return 0;
}
fs_initcall(xen_spinlock_debugfs);

#endif  /* CONFIG_XEN_DEBUG_FS */