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

#include <asm/barrier.h>
#include <asm/ldcw.h>
#include <asm/processor.h>
#include <asm/spinlock_types.h>

static inline void arch_spin_val_check(int lock_val)
{
    if (IS_ENABLED(CONFIG_LIGHTWEIGHT_SPINLOCK_CHECK))
        asm volatile(    "andcm,= %0,%1,%%r0\n"
                ".word %2\n"
        : : "r" (lock_val), "r" (__ARCH_SPIN_LOCK_UNLOCKED_VAL),
            "i" (SPINLOCK_BREAK_INSN));
}

static inline int arch_spin_is_locked(arch_spinlock_t *x)
{
    volatile unsigned int *a;
    int lock_val;

    a = __ldcw_align(x);
    lock_val = READ_ONCE(*a);
    arch_spin_val_check(lock_val);
    return (lock_val == 0);
}

static inline void arch_spin_lock(arch_spinlock_t *x)
{
    volatile unsigned int *a;

    a = __ldcw_align(x);
    do {
        int lock_val_old;

        lock_val_old = __ldcw(a);
        arch_spin_val_check(lock_val_old);
        if (lock_val_old)
            return;    /* got lock */

        /* wait until we should try to get lock again */
        while (*a == 0)
            continue;
    } while (1);
}

static inline void arch_spin_unlock(arch_spinlock_t *x)
{
    volatile unsigned int *a;

    a = __ldcw_align(x);
    /* Release with ordered store. */
    __asm__ __volatile__("stw,ma %0,0(%1)"
        : : "r"(__ARCH_SPIN_LOCK_UNLOCKED_VAL), "r"(a) : "memory");
}

static inline int arch_spin_trylock(arch_spinlock_t *x)
{
    volatile unsigned int *a;
    int lock_val;

    a = __ldcw_align(x);
    lock_val = __ldcw(a);
    arch_spin_val_check(lock_val);
    return lock_val != 0;
}

/*
 * Read-write spinlocks, allowing multiple readers but only one writer.
 * Unfair locking as Writers could be starved indefinitely by Reader(s)
 *
 * The spinlock itself is contained in @counter and access to it is
 * serialized with @lock_mutex.
 */

/* 1 - lock taken successfully */
static inline int arch_read_trylock(arch_rwlock_t *rw)
{
    int ret = 0;
    unsigned long flags;

    local_irq_save(flags);
    arch_spin_lock(&(rw->lock_mutex));

    /*
     * zero means writer holds the lock exclusively, deny Reader.
     * Otherwise grant lock to first/subseq reader
     */
    if (rw->counter > 0) {
        rw->counter--;
        ret = 1;
    }

    arch_spin_unlock(&(rw->lock_mutex));
    local_irq_restore(flags);

    return ret;
}

/* 1 - lock taken successfully */
static inline int arch_write_trylock(arch_rwlock_t *rw)
{
    int ret = 0;
    unsigned long flags;

    local_irq_save(flags);
    arch_spin_lock(&(rw->lock_mutex));

    /*
     * If reader(s) hold lock (lock < __ARCH_RW_LOCK_UNLOCKED__),
     * deny writer. Otherwise if unlocked grant to writer
     * Hence the claim that Linux rwlocks are unfair to writers.
     * (can be starved for an indefinite time by readers).
     */
    if (rw->counter == __ARCH_RW_LOCK_UNLOCKED__) {
        rw->counter = 0;
        ret = 1;
    }
    arch_spin_unlock(&(rw->lock_mutex));
    local_irq_restore(flags);

    return ret;
}

static inline void arch_read_lock(arch_rwlock_t *rw)
{
    while (!arch_read_trylock(rw))
        cpu_relax();
}

static inline void arch_write_lock(arch_rwlock_t *rw)
{
    while (!arch_write_trylock(rw))
        cpu_relax();
}

static inline void arch_read_unlock(arch_rwlock_t *rw)
{
    unsigned long flags;

    local_irq_save(flags);
    arch_spin_lock(&(rw->lock_mutex));
    rw->counter++;
    arch_spin_unlock(&(rw->lock_mutex));
    local_irq_restore(flags);
}

static inline void arch_write_unlock(arch_rwlock_t *rw)
{
    unsigned long flags;

    local_irq_save(flags);
    arch_spin_lock(&(rw->lock_mutex));
    rw->counter = __ARCH_RW_LOCK_UNLOCKED__;
    arch_spin_unlock(&(rw->lock_mutex));
    local_irq_restore(flags);
}

#endif /* __ASM_SPINLOCK_H */