Linux Kernel之spin_lock之ARM实现

arch_spin_lock

arch_spin_trylock

arch_spin_unlock

arch_write_lock

arch_write_trylock

arch_write_unlock

arch_read_lock

arch_read_unlock

arch_read_trylock

unsigned long tmp;
	u32 newval;
	arch_spinlock_t lockval;


	prefetchw(&lock->slock);
	__asm__ __volatile__(
"1:	ldrex	%0, [%3]\n"
"	add	%1, %0, %4\n"
"	strex	%2, %1, [%3]\n"
"	teq	%2, #0\n"
"	bne	1b"
	: "=&r" (lockval), "=&r" (newval), "=&r" (tmp)
	: "r" (&lock->slock), "I" (1 << TICKET_SHIFT)
	: "cc");


	while (lockval.tickets.next != lockval.tickets.owner) {
		wfe();
		lockval.tickets.owner = ACCESS_ONCE(lock->tickets.owner);
	}


	smp_mb();
}


static inline int arch_spin_trylock(arch_spinlock_t *lock)
{
	unsigned long contended, res;
	u32 slock;


	prefetchw(&lock->slock);
	do {
		__asm__ __volatile__(
		"	ldrex	%0, [%3]\n"
		"	mov	%2, #0\n"
		"	subs	%1, %0, %0, ror #16\n"
		"	addeq	%0, %0, %4\n"
		"	strexeq	%2, %0, [%3]"
		: "=&r" (slock), "=&r" (contended), "=&r" (res)
		: "r" (&lock->slock), "I" (1 << TICKET_SHIFT)
		: "cc");
	} while (res);


	if (!contended) {
		smp_mb();
		return 1;
	} else {
		return 0;
	}
}


static inline void arch_spin_unlock(arch_spinlock_t *lock)
{
	smp_mb();
	lock->tickets.owner++;
	dsb_sev();
}

/*
 * RWLOCKS
 *
 *
 * Write locks are easy - we just set bit 31.  When unlocking, we can
 * just write zero since the lock is exclusively held.
 */


static inline void arch_write_lock(arch_rwlock_t *rw)
{
	unsigned long tmp;


	prefetchw(&rw->lock);
	__asm__ __volatile__(
"1:	ldrex	%0, [%1]\n"
"	teq	%0, #0\n"
	WFE("ne")
"	strexeq	%0, %2, [%1]\n"
"	teq	%0, #0\n"
"	bne	1b"
	: "=&r" (tmp)
	: "r" (&rw->lock), "r" (0x80000000)
	: "cc");


	smp_mb();
}


static inline int arch_write_trylock(arch_rwlock_t *rw)
{
	unsigned long contended, res;


	prefetchw(&rw->lock);
	do {
		__asm__ __volatile__(
		"	ldrex	%0, [%2]\n"
		"	mov	%1, #0\n"
		"	teq	%0, #0\n"
		"	strexeq	%1, %3, [%2]"
		: "=&r" (contended), "=&r" (res)
		: "r" (&rw->lock), "r" (0x80000000)
		: "cc");
	} while (res);


	if (!contended) {
		smp_mb();
		return 1;
	} else {
		return 0;
	}
}


static inline void arch_write_unlock(arch_rwlock_t *rw)
{
	smp_mb();


	__asm__ __volatile__(
	"str	%1, [%0]\n"
	:
	: "r" (&rw->lock), "r" (0)
	: "cc");


	dsb_sev();
}

/*
 * Read locks are a bit more hairy:
 *  - Exclusively load the lock value.
 *  - Increment it.
 *  - Store new lock value if positive, and we still own this location.
 *    If the value is negative, we've already failed.
 *  - If we failed to store the value, we want a negative result.
 *  - If we failed, try again.
 * Unlocking is similarly hairy.  We may have multiple read locks
 * currently active.  However, we know we won't have any write
 * locks.
 */
static inline void arch_read_lock(arch_rwlock_t *rw)
{
	unsigned long tmp, tmp2;


	prefetchw(&rw->lock);
	__asm__ __volatile__(
"1:	ldrex	%0, [%2]\n"
"	adds	%0, %0, #1\n"
"	strexpl	%1, %0, [%2]\n"
	WFE("mi")
"	rsbpls	%0, %1, #0\n"
"	bmi	1b"
	: "=&r" (tmp), "=&r" (tmp2)
	: "r" (&rw->lock)
	: "cc");


	smp_mb();
}


static inline void arch_read_unlock(arch_rwlock_t *rw)
{
	unsigned long tmp, tmp2;


	smp_mb();


	prefetchw(&rw->lock);
	__asm__ __volatile__(
"1:	ldrex	%0, [%2]\n"
"	sub	%0, %0, #1\n"
"	strex	%1, %0, [%2]\n"
"	teq	%1, #0\n"
"	bne	1b"
	: "=&r" (tmp), "=&r" (tmp2)
	: "r" (&rw->lock)
	: "cc");


	if (tmp == 0)
		dsb_sev();
}


static inline int arch_read_trylock(arch_rwlock_t *rw)
{
	unsigned long contended, res;


	prefetchw(&rw->lock);
	do {
		__asm__ __volatile__(
		"	ldrex	%0, [%2]\n"
		"	mov	%1, #0\n"
		"	adds	%0, %0, #1\n"
		"	strexpl	%1, %0, [%2]"
		: "=&r" (contended), "=&r" (res)
		: "r" (&rw->lock)
		: "cc");
	} while (res);


	/* If the lock is negative, then it is already held for write. */
	if (contended < 0x80000000) {
		smp_mb();
		return 1;
	} else {
		return 0;
	}
}