/*
 * 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>
#include <asm/pvclock.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) + HPET_COUNTER);
}

#ifdef CONFIG_PARAVIRT_CLOCK

static notrace const struct pvclock_vsyscall_time_info *get_pvti(int cpu)
{
        const struct pvclock_vsyscall_time_info *pvti_base;
        int idx = cpu / (PAGE_SIZE/PVTI_SIZE);
        int offset = cpu % (PAGE_SIZE/PVTI_SIZE);

        BUG_ON(PVCLOCK_FIXMAP_BEGIN + idx > PVCLOCK_FIXMAP_END);

        pvti_base = (struct pvclock_vsyscall_time_info *)
                    __fix_to_virt(PVCLOCK_FIXMAP_BEGIN+idx);

        return &pvti_base[offset];
}

static notrace cycle_t vread_pvclock(int *mode)
{
        const struct pvclock_vsyscall_time_info *pvti;
        cycle_t ret;
        u64 last;
        u32 version;
        u8 flags;
        unsigned cpu, cpu1;


        /*
         * Note: hypervisor must guarantee that:
         * 1. cpu ID number maps 1:1 to per-CPU pvclock time info.
         * 2. that per-CPU pvclock time info is updated if the
         *    underlying CPU changes.
         * 3. that version is increased whenever underlying CPU
         *    changes.
         *
         */
        do {
                cpu = __getcpu() & VGETCPU_CPU_MASK;
                /* TODO: We can put vcpu id into higher bits of pvti.version.
                 * This will save a couple of cycles by getting rid of
                 * __getcpu() calls (Gleb).
                 */

                pvti = get_pvti(cpu);

                version = __pvclock_read_cycles(&pvti->pvti, &ret, &flags);

                /*
                 * Test we're still on the cpu as well as the version.
                 * We could have been migrated just after the first
                 * vgetcpu but before fetching the version, so we
                 * wouldn't notice a version change.
                 */
                cpu1 = __getcpu() & VGETCPU_CPU_MASK;
        } while (unlikely(cpu != cpu1 ||
                          (pvti->pvti.version & 1) ||
                          pvti->pvti.version != version));

        if (unlikely(!(flags & PVCLOCK_TSC_STABLE_BIT)))
                *mode = VCLOCK_NONE;

        /* refer to tsc.c read_tsc() comment for rationale */
        last = VVAR(vsyscall_gtod_data).clock.cycle_last;

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

        return last;
}
#endif

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 long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
{
        long ret;

        asm("syscall" : "=a" (ret) :
            "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
        return ret;
}


notrace static inline u64 vgetsns(int *mode)
{
        long v;
        cycles_t cycles;
        if (gtod->clock.vclock_mode == VCLOCK_TSC)
                cycles = vread_tsc();
        else if (gtod->clock.vclock_mode == VCLOCK_HPET)
                cycles = vread_hpet();
#ifdef CONFIG_PARAVIRT_CLOCK
        else if (gtod->clock.vclock_mode == VCLOCK_PVCLOCK)
                cycles = vread_pvclock(mode);
#endif
        else
                return 0;
        v = (cycles - gtod->clock.cycle_last) & gtod->clock.mask;
        return v * gtod->clock.mult;
}

/* Code size doesn't matter (vdso is 4k anyway) and this is faster. */
notrace static int __always_inline do_realtime(struct timespec *ts)
{
        unsigned long seq;
        u64 ns;
        int mode;

        ts->tv_nsec = 0;
        do {
                seq = read_seqcount_begin(&gtod->seq);
                mode = gtod->clock.vclock_mode;
                ts->tv_sec = gtod->wall_time_sec;
                ns = gtod->wall_time_snsec;
                ns += vgetsns(&mode);
                ns >>= gtod->clock.shift;
        } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));

        timespec_add_ns(ts, ns);
        return mode;
}

notrace static int do_monotonic(struct timespec *ts)
{
        unsigned long seq;
        u64 ns;
        int mode;

        ts->tv_nsec = 0;
        do {
                seq = read_seqcount_begin(&gtod->seq);
                mode = gtod->clock.vclock_mode;
                ts->tv_sec = gtod->monotonic_time_sec;
                ns = gtod->monotonic_time_snsec;
                ns += vgetsns(&mode);
                ns >>= gtod->clock.shift;
        } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
        timespec_add_ns(ts, ns);

        return mode;
}

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

notrace static int do_monotonic_coarse(struct timespec *ts)
{
        unsigned long seq;
        do {
                seq = read_seqcount_begin(&gtod->seq);
                ts->tv_sec = gtod->monotonic_time_coarse.tv_sec;
                ts->tv_nsec = gtod->monotonic_time_coarse.tv_nsec;
        } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));

        return 0;
}

notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
{
        int ret = VCLOCK_NONE;

        switch (clock) {
        case CLOCK_REALTIME:
                ret = do_realtime(ts);
                break;
        case CLOCK_MONOTONIC:
                ret = do_monotonic(ts);
                break;
        case CLOCK_REALTIME_COARSE:
                return do_realtime_coarse(ts);
        case CLOCK_MONOTONIC_COARSE:
                return do_monotonic_coarse(ts);
        }

        if (ret == VCLOCK_NONE)
                return vdso_fallback_gettime(clock, ts);
        return 0;
}
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 = VCLOCK_NONE;

        if (likely(tv != NULL)) {
                BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
                             offsetof(struct timespec, tv_nsec) ||
                             sizeof(*tv) != sizeof(struct timespec));
                ret = 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;
        }

        if (ret == VCLOCK_NONE)
                return vdso_fallback_gtod(tv, tz);
        return 0;
}
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")));