linux/arch/powerpc/lib/locks.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Spin and read/write lock operations.
 *
 * Copyright (C) 2001-2004 Paul Mackerras <paulus@au.ibm.com>, IBM
 * Copyright (C) 2001 Anton Blanchard <anton@au.ibm.com>, IBM
 * Copyright (C) 2002 Dave Engebretsen <engebret@us.ibm.com>, IBM
 *   Rework to support virtual processors
 */

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

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

void splpar_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 = yield_count_of(holder_cpu);
	if ((yield_count & 1) == 0)
		return;		/* virtual cpu is currently running */
	rmb();
	if (lock->slock != lock_value)
		return;		/* something has changed */
	yield_to_preempted(holder_cpu, yield_count);
}
EXPORT_SYMBOL_GPL(splpar_spin_yield);

/*
 * 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 splpar_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 = yield_count_of(holder_cpu);
	if ((yield_count & 1) == 0)
		return;		/* virtual cpu is currently running */
	rmb();
	if (rw->lock != lock_value)
		return;		/* something has changed */
	yield_to_preempted(holder_cpu, yield_count);
}
#endif