arch/arm64/include/asm/spinlock.h

/*
 * Copyright (C) 2012 ARM Ltd.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#ifndef __ASM_SPINLOCK_H
#define __ASM_SPINLOCK_H

#include <asm/lse.h>
#include <asm/spinlock_types.h>
#include <asm/processor.h>

/*
 * Spinlock implementation.
 *
 * The memory barriers are implicit with the load-acquire and store-release
 * instructions.
 */

static inline void arch_spin_lock(arch_spinlock_t *lock)
{
	unsigned int tmp;
	arch_spinlock_t lockval, newval;

	asm volatile(
	/* Atomically increment the next ticket. */
	ARM64_LSE_ATOMIC_INSN(
	/* LL/SC */
"	prfm	pstl1strm, %3\n"
"1:	ldaxr	%w0, %3\n"
"	add	%w1, %w0, %w5\n"
"	stxr	%w2, %w1, %3\n"
"	cbnz	%w2, 1b\n",
	/* LSE atomics */
"	mov	%w2, %w5\n"
"	ldadda	%w2, %w0, %3\n"
	__nops(3)
	)

	/* Did we get the lock? */
"	eor	%w1, %w0, %w0, ror #16\n"
"	cbz	%w1, 3f\n"
	/*
	 * No: spin on the owner. Send a local event to avoid missing an
	 * unlock before the exclusive load.
	 */
"	sevl\n"
"2:	wfe\n"
"	ldaxrh	%w2, %4\n"
"	eor	%w1, %w2, %w0, lsr #16\n"
"	cbnz	%w1, 2b\n"
	/* We got the lock. Critical section starts here. */
"3:"
	: "=&r" (lockval), "=&r" (newval), "=&r" (tmp), "+Q" (*lock)
	: "Q" (lock->owner), "I" (1 << TICKET_SHIFT)
	: "memory");
}

static inline int arch_spin_trylock(arch_spinlock_t *lock)
{
	unsigned int tmp;
	arch_spinlock_t lockval;

	asm volatile(ARM64_LSE_ATOMIC_INSN(
	/* LL/SC */
	"	prfm	pstl1strm, %2\n"
	"1:	ldaxr	%w0, %2\n"
	"	eor	%w1, %w0, %w0, ror #16\n"
	"	cbnz	%w1, 2f\n"
	"	add	%w0, %w0, %3\n"
	"	stxr	%w1, %w0, %2\n"
	"	cbnz	%w1, 1b\n"
	"2:",
	/* LSE atomics */
	"	ldr	%w0, %2\n"
	"	eor	%w1, %w0, %w0, ror #16\n"
	"	cbnz	%w1, 1f\n"
	"	add	%w1, %w0, %3\n"
	"	casa	%w0, %w1, %2\n"
	"	sub	%w1, %w1, %3\n"
	"	eor	%w1, %w1, %w0\n"
	"1:")
	: "=&r" (lockval), "=&r" (tmp), "+Q" (*lock)
	: "I" (1 << TICKET_SHIFT)
	: "memory");

	return !tmp;
}

static inline void arch_spin_unlock(arch_spinlock_t *lock)
{
	unsigned long tmp;

	asm volatile(ARM64_LSE_ATOMIC_INSN(
	/* LL/SC */
	"	ldrh	%w1, %0\n"
	"	add	%w1, %w1, #1\n"
	"	stlrh	%w1, %0",
	/* LSE atomics */
	"	mov	%w1, #1\n"
	"	staddlh	%w1, %0\n"
	__nops(1))
	: "=Q" (lock->owner), "=&r" (tmp)
	:
	: "memory");
}

static inline int arch_spin_value_unlocked(arch_spinlock_t lock)
{
	return lock.owner == lock.next;
}

static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
	/*
	 * Ensure prior spin_lock operations to other locks have completed
	 * on this CPU before we test whether "lock" is locked.
	 */
	smp_mb(); /* ^^^ */
	return !arch_spin_value_unlocked(READ_ONCE(*lock));
}

static inline int arch_spin_is_contended(arch_spinlock_t *lock)
{
	arch_spinlock_t lockval = READ_ONCE(*lock);
	return (lockval.next - lockval.owner) > 1;
}
#define arch_spin_is_contended	arch_spin_is_contended

#include <asm/qrwlock.h>

/* See include/linux/spinlock.h */
#define smp_mb__after_spinlock()	smp_mb()

#endif /* __ASM_SPINLOCK_H */