locks.c

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/*
 * Spin and read/write lock operations.
 *
 * Copyright (C) 2001-2004 Paul Mackerras <[email protected]>, IBM
 * Copyright (C) 2001 Anton Blanchard <[email protected]>, IBM
 * Copyright (C) 2002 Dave Engebretsen <[email protected]>, IBM
 *   Rework to support virtual processors
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/kernel.h>
#include <linux/spinlock.h>
#include <linux/export.h>
#include <linux/stringify.h>
#include <linux/smp.h>

/* waiting for a spinlock... */
#if defined(CONFIG_PPC_SPLPAR)
#include <asm/hvcall.h>
#include <asm/smp.h>

void __spin_yield(arch_spinlock_t *lock)
{
    unsigned int lock_value, holder_cpu, yield_count;

    lock_value = lock->slock;
    if (lock_value == 0)
        return;
    holder_cpu = lock_value & 0xffff;
    BUG_ON(holder_cpu >= NR_CPUS);
    yield_count = lppaca_of(holder_cpu).yield_count;
    if ((yield_count & 1) == 0)
        return;     /* virtual cpu is currently running */
    rmb();
    if (lock->slock != lock_value)
        return;     /* something has changed */
    plpar_hcall_norets(H_CONFER,
        get_hard_smp_processor_id(holder_cpu), yield_count);
}

/*
 * Waiting for a read lock or a write lock on a rwlock...
 * This turns out to be the same for read and write locks, since
 * we only know the holder if it is write-locked.
 */
void __rw_yield(arch_rwlock_t *rw)
{
    int lock_value;
    unsigned int holder_cpu, yield_count;

    lock_value = rw->lock;
    if (lock_value >= 0)
        return;     /* no write lock at present */
    holder_cpu = lock_value & 0xffff;
    BUG_ON(holder_cpu >= NR_CPUS);
    yield_count = lppaca_of(holder_cpu).yield_count;
    if ((yield_count & 1) == 0)
        return;     /* virtual cpu is currently running */
    rmb();
    if (rw->lock != lock_value)
        return;     /* something has changed */
    plpar_hcall_norets(H_CONFER,
        get_hard_smp_processor_id(holder_cpu), yield_count);
}
#endif

void arch_spin_unlock_wait(arch_spinlock_t *lock)
{
    while (lock->slock) {
        HMT_low();
        if (SHARED_PROCESSOR)
            __spin_yield(lock);
    }
    HMT_medium();
}

EXPORT_SYMBOL(arch_spin_unlock_wait);