/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __VDSO_HELPERS_H
#define __VDSO_HELPERS_H

#ifndef __ASSEMBLY__

#include <asm/barrier.h>
#include <vdso/datapage.h>

static __always_inline u32 vdso_read_begin(const struct vdso_clock *vc)
{
        u32 seq;

        while (unlikely((seq = READ_ONCE(vc->seq)) & 1))
                cpu_relax();

        smp_rmb();
        return seq;
}

static __always_inline u32 vdso_read_retry(const struct vdso_clock *vc,
                                           u32 start)
{
        u32 seq;

        smp_rmb();
        seq = READ_ONCE(vc->seq);
        return seq != start;
}

static __always_inline void vdso_write_seq_begin(struct vdso_clock *vc)
{
        /*
         * WRITE_ONCE() is required otherwise the compiler can validly tear
         * updates to vc->seq and it is possible that the value seen by the
         * reader is inconsistent.
         */
        WRITE_ONCE(vc->seq, vc->seq + 1);
}

static __always_inline void vdso_write_seq_end(struct vdso_clock *vc)
{
        /*
         * WRITE_ONCE() is required otherwise the compiler can validly tear
         * updates to vc->seq and it is possible that the value seen by the
         * reader is inconsistent.
         */
        WRITE_ONCE(vc->seq, vc->seq + 1);
}

static __always_inline void vdso_write_begin_clock(struct vdso_clock *vc)
{
        vdso_write_seq_begin(vc);
        /* Ensure the sequence invalidation is visible before data is modified */
        smp_wmb();
}

static __always_inline void vdso_write_end_clock(struct vdso_clock *vc)
{
        /* Ensure the data update is visible before the sequence is set valid again */
        smp_wmb();
        vdso_write_seq_end(vc);
}

static __always_inline void vdso_write_begin(struct vdso_time_data *vd)
{
        struct vdso_clock *vc = vd->clock_data;

        vdso_write_seq_begin(&vc[CS_HRES_COARSE]);
        vdso_write_seq_begin(&vc[CS_RAW]);
        /* Ensure the sequence invalidation is visible before data is modified */
        smp_wmb();
}

static __always_inline void vdso_write_end(struct vdso_time_data *vd)
{
        struct vdso_clock *vc = vd->clock_data;

        /* Ensure the data update is visible before the sequence is set valid again */
        smp_wmb();
        vdso_write_seq_end(&vc[CS_HRES_COARSE]);
        vdso_write_seq_end(&vc[CS_RAW]);
}

#endif /* !__ASSEMBLY__ */

#endif /* __VDSO_HELPERS_H */