/*
 * Copyright 2006 Andi Kleen, SUSE Labs.
 * Subject to the GNU Public License, v.2
 *
 * Fast user context implementation of clock_gettime, gettimeofday, and time.
 *
 * The code should have no internal unresolved relocations.
 * Check with readelf after changing.
 */

/* Disable profiling for userspace code: */
#define DISABLE_BRANCH_PROFILING

#include <linux/kernel.h>
#include <linux/posix-timers.h>
#include <linux/time.h>
#include <linux/string.h>
#include <asm/vsyscall.h>
#include <asm/fixmap.h>
#include <asm/vgtod.h>
#include <asm/timex.h>
#include <asm/hpet.h>
#include <asm/unistd.h>
#include <asm/io.h>

#define gtod (&VVAR(vsyscall_gtod_data))

notrace static cycle_t vread_tsc(void)
{
        cycle_t ret;
        u64 last;

        /*
         * Empirically, a fence (of type that depends on the CPU)
         * before rdtsc is enough to ensure that rdtsc is ordered
         * with respect to loads.  The various CPU manuals are unclear
         * as to whether rdtsc can be reordered with later loads,
         * but no one has ever seen it happen.
         */
        rdtsc_barrier();
        ret = (cycle_t)vget_cycles();

        last = VVAR(vsyscall_gtod_data).clock.cycle_last;

        if (likely(ret >= last))
                return ret;

        /*
         * GCC likes to generate cmov here, but this branch is extremely
         * predictable (it's just a funciton of time and the likely is
         * very likely) and there's a data dependence, so force GCC
         * to generate a branch instead.  I don't barrier() because
         * we don't actually need a barrier, and if this function
         * ever gets inlined it will generate worse code.
         */
        asm volatile ("");
        return last;
}

static notrace cycle_t vread_hpet(void)
{
        return readl((const void __iomem *)fix_to_virt(VSYSCALL_HPET) + 0xf0);
}

notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
{
        long ret;
        asm("syscall" : "=a" (ret) :
            "0" (__NR_clock_gettime),"D" (clock), "S" (ts) : "memory");
        return ret;
}

notrace static inline long vgetns(void)
{
        long v;
        cycles_t cycles;
        if (gtod->clock.vclock_mode == VCLOCK_TSC)
                cycles = vread_tsc();
        else
                cycles = vread_hpet();
        v = (cycles - gtod->clock.cycle_last) & gtod->clock.mask;
        return (v * gtod->clock.mult) >> gtod->clock.shift;
}

notrace static noinline int do_realtime(struct timespec *ts)
{
        unsigned long seq, ns;
        do {
                seq = read_seqbegin(&gtod->lock);
                ts->tv_sec = gtod->wall_time_sec;
                ts->tv_nsec = gtod->wall_time_nsec;
                ns = vgetns();
        } while (unlikely(read_seqretry(&gtod->lock, seq)));
        timespec_add_ns(ts, ns);
        return 0;
}

notrace static noinline int do_monotonic(struct timespec *ts)
{
        unsigned long seq, ns, secs;
        do {
                seq = read_seqbegin(&gtod->lock);
                secs = gtod->wall_time_sec;
                ns = gtod->wall_time_nsec + vgetns();
                secs += gtod->wall_to_monotonic.tv_sec;
                ns += gtod->wall_to_monotonic.tv_nsec;
        } while (unlikely(read_seqretry(&gtod->lock, seq)));

        /* wall_time_nsec, vgetns(), and wall_to_monotonic.tv_nsec
         * are all guaranteed to be nonnegative.
         */
        while (ns >= NSEC_PER_SEC) {
                ns -= NSEC_PER_SEC;
                ++secs;
        }
        ts->tv_sec = secs;
        ts->tv_nsec = ns;

        return 0;
}

notrace static noinline int do_realtime_coarse(struct timespec *ts)
{
        unsigned long seq;
        do {
                seq = read_seqbegin(&gtod->lock);
                ts->tv_sec = gtod->wall_time_coarse.tv_sec;
                ts->tv_nsec = gtod->wall_time_coarse.tv_nsec;
        } while (unlikely(read_seqretry(&gtod->lock, seq)));
        return 0;
}

notrace static noinline int do_monotonic_coarse(struct timespec *ts)
{
        unsigned long seq, ns, secs;
        do {
                seq = read_seqbegin(&gtod->lock);
                secs = gtod->wall_time_coarse.tv_sec;
                ns = gtod->wall_time_coarse.tv_nsec;
                secs += gtod->wall_to_monotonic.tv_sec;
                ns += gtod->wall_to_monotonic.tv_nsec;
        } while (unlikely(read_seqretry(&gtod->lock, seq)));

        /* wall_time_nsec and wall_to_monotonic.tv_nsec are
         * guaranteed to be between 0 and NSEC_PER_SEC.
         */
        if (ns >= NSEC_PER_SEC) {
                ns -= NSEC_PER_SEC;
                ++secs;
        }
        ts->tv_sec = secs;
        ts->tv_nsec = ns;

        return 0;
}

notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
{
        switch (clock) {
        case CLOCK_REALTIME:
                if (likely(gtod->clock.vclock_mode != VCLOCK_NONE))
                        return do_realtime(ts);
                break;
        case CLOCK_MONOTONIC:
                if (likely(gtod->clock.vclock_mode != VCLOCK_NONE))
                        return do_monotonic(ts);
                break;
        case CLOCK_REALTIME_COARSE:
                return do_realtime_coarse(ts);
        case CLOCK_MONOTONIC_COARSE:
                return do_monotonic_coarse(ts);
        }

        return vdso_fallback_gettime(clock, ts);
}
int clock_gettime(clockid_t, struct timespec *)
        __attribute__((weak, alias("__vdso_clock_gettime")));

notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
{
        long ret;
        if (likely(gtod->clock.vclock_mode != VCLOCK_NONE)) {
                if (likely(tv != NULL)) {
                        BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
                                     offsetof(struct timespec, tv_nsec) ||
                                     sizeof(*tv) != sizeof(struct timespec));
                        do_realtime((struct timespec *)tv);
                        tv->tv_usec /= 1000;
                }
                if (unlikely(tz != NULL)) {
                        /* Avoid memcpy. Some old compilers fail to inline it */
                        tz->tz_minuteswest = gtod->sys_tz.tz_minuteswest;
                        tz->tz_dsttime = gtod->sys_tz.tz_dsttime;
                }
                return 0;
        }
        asm("syscall" : "=a" (ret) :
            "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
        return ret;
}
int gettimeofday(struct timeval *, struct timezone *)
        __attribute__((weak, alias("__vdso_gettimeofday")));

/*
 * This will break when the xtime seconds get inaccurate, but that is
 * unlikely
 */
notrace time_t __vdso_time(time_t *t)
{
        /* This is atomic on x86_64 so we don't need any locks. */
        time_t result = ACCESS_ONCE(VVAR(vsyscall_gtod_data).wall_time_sec);

        if (t)
                *t = result;
        return result;
}
int time(time_t *t)
        __attribute__((weak, alias("__vdso_time")));