[linux-2.6-block.git] / arch / arc / include / asm / spinlock.h

/*
 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
 *
 * 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.
 */

#ifndef __ASM_SPINLOCK_H
#define __ASM_SPINLOCK_H

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

#define arch_spin_is_locked(x)	((x)->slock != __ARCH_SPIN_LOCK_UNLOCKED__)
#define arch_spin_lock_flags(lock, flags)	arch_spin_lock(lock)

static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
{
	smp_cond_load_acquire(&lock->slock, !VAL);
}

#ifdef CONFIG_ARC_HAS_LLSC

static inline void arch_spin_lock(arch_spinlock_t *lock)
{
	unsigned int val;

	smp_mb();

	__asm__ __volatile__(
	"1:	llock	%[val], [%[slock]]	\n"
	"	breq	%[val], %[LOCKED], 1b	\n"	/* spin while LOCKED */
	"	scond	%[LOCKED], [%[slock]]	\n"	/* acquire */
	"	bnz	1b			\n"
	"					\n"
	: [val]		"=&r"	(val)
	: [slock]	"r"	(&(lock->slock)),
	  [LOCKED]	"r"	(__ARCH_SPIN_LOCK_LOCKED__)
	: "memory", "cc");

	smp_mb();
}

/* 1 - lock taken successfully */
static inline int arch_spin_trylock(arch_spinlock_t *lock)
{
	unsigned int val, got_it = 0;

	smp_mb();

	__asm__ __volatile__(
	"1:	llock	%[val], [%[slock]]	\n"
	"	breq	%[val], %[LOCKED], 4f	\n"	/* already LOCKED, just bail */
	"	scond	%[LOCKED], [%[slock]]	\n"	/* acquire */
	"	bnz	1b			\n"
	"	mov	%[got_it], 1		\n"
	"4:					\n"
	"					\n"
	: [val]		"=&r"	(val),
	  [got_it]	"+&r"	(got_it)
	: [slock]	"r"	(&(lock->slock)),
	  [LOCKED]	"r"	(__ARCH_SPIN_LOCK_LOCKED__)
	: "memory", "cc");

	smp_mb();

	return got_it;
}

static inline void arch_spin_unlock(arch_spinlock_t *lock)
{
	smp_mb();

	lock->slock = __ARCH_SPIN_LOCK_UNLOCKED__;

	smp_mb();
}

/*
 * Read-write spinlocks, allowing multiple readers but only one writer.
 * Unfair locking as Writers could be starved indefinitely by Reader(s)
 */

static inline void arch_read_lock(arch_rwlock_t *rw)
{
	unsigned int val;

	smp_mb();

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

	__asm__ __volatile__(
	"1:	llock	%[val], [%[rwlock]]	\n"
	"	brls	%[val], %[WR_LOCKED], 1b\n"	/* <= 0: spin while write locked */
	"	sub	%[val], %[val], 1	\n"	/* reader lock */
	"	scond	%[val], [%[rwlock]]	\n"
	"	bnz	1b			\n"
	"					\n"
	: [val]		"=&r"	(val)
	: [rwlock]	"r"	(&(rw->counter)),
	  [WR_LOCKED]	"ir"	(0)
	: "memory", "cc");

	smp_mb();
}

/* 1 - lock taken successfully */
static inline int arch_read_trylock(arch_rwlock_t *rw)
{
	unsigned int val, got_it = 0;

	smp_mb();

	__asm__ __volatile__(
	"1:	llock	%[val], [%[rwlock]]	\n"
	"	brls	%[val], %[WR_LOCKED], 4f\n"	/* <= 0: already write locked, bail */
	"	sub	%[val], %[val], 1	\n"	/* counter-- */
	"	scond	%[val], [%[rwlock]]	\n"
	"	bnz	1b			\n"	/* retry if collided with someone */
	"	mov	%[got_it], 1		\n"
	"					\n"
	"4: ; --- done ---			\n"

	: [val]		"=&r"	(val),
	  [got_it]	"+&r"	(got_it)
	: [rwlock]	"r"	(&(rw->counter)),
	  [WR_LOCKED]	"ir"	(0)
	: "memory", "cc");

	smp_mb();

	return got_it;
}

static inline void arch_write_lock(arch_rwlock_t *rw)
{
	unsigned int val;

	smp_mb();

	/*
	 * 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;
	 *	}
	 */

	__asm__ __volatile__(
	"1:	llock	%[val], [%[rwlock]]	\n"
	"	brne	%[val], %[UNLOCKED], 1b	\n"	/* while !UNLOCKED spin */
	"	mov	%[val], %[WR_LOCKED]	\n"
	"	scond	%[val], [%[rwlock]]	\n"
	"	bnz	1b			\n"
	"					\n"
	: [val]		"=&r"	(val)
	: [rwlock]	"r"	(&(rw->counter)),
	  [UNLOCKED]	"ir"	(__ARCH_RW_LOCK_UNLOCKED__),
	  [WR_LOCKED]	"ir"	(0)
	: "memory", "cc");

	smp_mb();
}

/* 1 - lock taken successfully */
static inline int arch_write_trylock(arch_rwlock_t *rw)
{
	unsigned int val, got_it = 0;

	smp_mb();

	__asm__ __volatile__(
	"1:	llock	%[val], [%[rwlock]]	\n"
	"	brne	%[val], %[UNLOCKED], 4f	\n"	/* !UNLOCKED, bail */
	"	mov	%[val], %[WR_LOCKED]	\n"
	"	scond	%[val], [%[rwlock]]	\n"
	"	bnz	1b			\n"	/* retry if collided with someone */
	"	mov	%[got_it], 1		\n"
	"					\n"
	"4: ; --- done ---			\n"

	: [val]		"=&r"	(val),
	  [got_it]	"+&r"	(got_it)
	: [rwlock]	"r"	(&(rw->counter)),
	  [UNLOCKED]	"ir"	(__ARCH_RW_LOCK_UNLOCKED__),
	  [WR_LOCKED]	"ir"	(0)
	: "memory", "cc");

	smp_mb();

	return got_it;
}

static inline void arch_read_unlock(arch_rwlock_t *rw)
{
	unsigned int val;

	smp_mb();

	/*
	 * rw->counter++;
	 */
	__asm__ __volatile__(
	"1:	llock	%[val], [%[rwlock]]	\n"
	"	add	%[val], %[val], 1	\n"
	"	scond	%[val], [%[rwlock]]	\n"
	"	bnz	1b			\n"
	"					\n"
	: [val]		"=&r"	(val)
	: [rwlock]	"r"	(&(rw->counter))
	: "memory", "cc");

	smp_mb();
}

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

	rw->counter = __ARCH_RW_LOCK_UNLOCKED__;

	smp_mb();
}

#else	/* !CONFIG_ARC_HAS_LLSC */

static inline void arch_spin_lock(arch_spinlock_t *lock)
{
	unsigned int val = __ARCH_SPIN_LOCK_LOCKED__;

	/*
	 * This smp_mb() is technically superfluous, we only need the one
	 * after the lock for providing the ACQUIRE semantics.
	 * However doing the "right" thing was regressing hackbench
	 * so keeping this, pending further investigation
	 */
	smp_mb();

	__asm__ __volatile__(
	"1:	ex  %0, [%1]		\n"
	"	breq  %0, %2, 1b	\n"
	: "+&r" (val)
	: "r"(&(lock->slock)), "ir"(__ARCH_SPIN_LOCK_LOCKED__)
	: "memory");

	/*
	 * ACQUIRE barrier to ensure load/store after taking the lock
	 * don't "bleed-up" out of the critical section (leak-in is allowed)
	 * http://www.spinics.net/lists/kernel/msg2010409.html
	 *
	 * ARCv2 only has load-load, store-store and all-all barrier
	 * thus need the full all-all barrier
	 */
	smp_mb();
}

/* 1 - lock taken successfully */
static inline int arch_spin_trylock(arch_spinlock_t *lock)
{
	unsigned int val = __ARCH_SPIN_LOCK_LOCKED__;

	smp_mb();

	__asm__ __volatile__(
	"1:	ex  %0, [%1]		\n"
	: "+r" (val)
	: "r"(&(lock->slock))
	: "memory");

	smp_mb();

	return (val == __ARCH_SPIN_LOCK_UNLOCKED__);
}

static inline void arch_spin_unlock(arch_spinlock_t *lock)
{
	unsigned int val = __ARCH_SPIN_LOCK_UNLOCKED__;

	/*
	 * RELEASE barrier: given the instructions avail on ARCv2, full barrier
	 * is the only option
	 */
	smp_mb();

	/*
	 * EX is not really required here, a simple STore of 0 suffices.
	 * However this causes tasklist livelocks in SystemC based SMP virtual
	 * platforms where the systemc core scheduler uses EX as a cue for
	 * moving to next core. Do a git log of this file for details
	 */
	__asm__ __volatile__(
	"	ex  %0, [%1]		\n"
	: "+r" (val)
	: "r"(&(lock->slock))
	: "memory");

	/*
	 * superfluous, but keeping for now - see pairing version in
	 * arch_spin_lock above
	 */
	smp_mb();
}

/*
 * 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);

	smp_mb();
	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

#define arch_read_can_lock(x)	((x)->counter > 0)
#define arch_write_can_lock(x)	((x)->counter == __ARCH_RW_LOCK_UNLOCKED__)

#define arch_read_lock_flags(lock, flags)	arch_read_lock(lock)
#define arch_write_lock_flags(lock, flags)	arch_write_lock(lock)

#define arch_spin_relax(lock)	cpu_relax()
#define arch_read_relax(lock)	cpu_relax()
#define arch_write_relax(lock)	cpu_relax()

#endif /* __ASM_SPINLOCK_H */
Commit	Line	Data
6e35fa2d VG	1	/*
	2	* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
	3	*
	4	* This program is free software; you can redistribute it and/or modify
	5	* it under the terms of the GNU General Public License version 2 as
	6	* published by the Free Software Foundation.
	7	*/
	8
	9	#ifndef __ASM_SPINLOCK_H
	10	#define __ASM_SPINLOCK_H
	11
	12	#include <asm/spinlock_types.h>
	13	#include <asm/processor.h>
	14	#include <asm/barrier.h>
	15
	16	#define arch_spin_is_locked(x) ((x)->slock != __ARCH_SPIN_LOCK_UNLOCKED__)
	17	#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
726328d9 PZ	18
	19	static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
	20	{
	21	smp_cond_load_acquire(&lock->slock, !VAL);
	22	}
6e35fa2d	23
ae7eae9e VG	24	#ifdef CONFIG_ARC_HAS_LLSC
	25
	26	static inline void arch_spin_lock(arch_spinlock_t *lock)
	27	{
	28	unsigned int val;
	29
	30	smp_mb();
	31
	32	__asm__ __volatile__(
	33	"1: llock %[val], [%[slock]] \n"
	34	" breq %[val], %[LOCKED], 1b \n" /* spin while LOCKED */
	35	" scond %[LOCKED], [%[slock]] \n" /* acquire */
	36	" bnz 1b \n"
	37	" \n"
	38	: [val] "=&r" (val)
	39	: [slock] "r" (&(lock->slock)),
	40	[LOCKED] "r" (__ARCH_SPIN_LOCK_LOCKED__)
	41	: "memory", "cc");
	42
	43	smp_mb();
	44	}
	45
	46	/* 1 - lock taken successfully */
	47	static inline int arch_spin_trylock(arch_spinlock_t *lock)
	48	{
	49	unsigned int val, got_it = 0;
	50
	51	smp_mb();
	52
	53	__asm__ __volatile__(
	54	"1: llock %[val], [%[slock]] \n"
	55	" breq %[val], %[LOCKED], 4f \n" /* already LOCKED, just bail */
	56	" scond %[LOCKED], [%[slock]] \n" /* acquire */
	57	" bnz 1b \n"
	58	" mov %[got_it], 1 \n"
	59	"4: \n"
	60	" \n"
	61	: [val] "=&r" (val),
	62	[got_it] "+&r" (got_it)
	63	: [slock] "r" (&(lock->slock)),
	64	[LOCKED] "r" (__ARCH_SPIN_LOCK_LOCKED__)
	65	: "memory", "cc");
	66
	67	smp_mb();
	68
	69	return got_it;
	70	}
	71
	72	static inline void arch_spin_unlock(arch_spinlock_t *lock)
	73	{
	74	smp_mb();
	75
	76	lock->slock = __ARCH_SPIN_LOCK_UNLOCKED__;
	77
	78	smp_mb();
	79	}
	80
69cbe630 VG	81	/*
	82	* Read-write spinlocks, allowing multiple readers but only one writer.
	83	* Unfair locking as Writers could be starved indefinitely by Reader(s)
	84	*/
	85
	86	static inline void arch_read_lock(arch_rwlock_t *rw)
	87	{
	88	unsigned int val;
	89
	90	smp_mb();
	91
	92	/*
	93	* zero means writer holds the lock exclusively, deny Reader.
	94	* Otherwise grant lock to first/subseq reader
	95	*
	96	* if (rw->counter > 0) {
	97	* rw->counter--;
	98	* ret = 1;
	99	* }
	100	*/
	101
	102	__asm__ __volatile__(
	103	"1: llock %[val], [%[rwlock]] \n"
	104	" brls %[val], %[WR_LOCKED], 1b\n" /* <= 0: spin while write locked */
	105	" sub %[val], %[val], 1 \n" /* reader lock */
	106	" scond %[val], [%[rwlock]] \n"
	107	" bnz 1b \n"
	108	" \n"
	109	: [val] "=&r" (val)
	110	: [rwlock] "r" (&(rw->counter)),
	111	[WR_LOCKED] "ir" (0)
	112	: "memory", "cc");
	113
	114	smp_mb();
	115	}
	116
	117	/* 1 - lock taken successfully */
	118	static inline int arch_read_trylock(arch_rwlock_t *rw)
	119	{
	120	unsigned int val, got_it = 0;
	121
	122	smp_mb();
	123
	124	__asm__ __volatile__(
	125	"1: llock %[val], [%[rwlock]] \n"
	126	" brls %[val], %[WR_LOCKED], 4f\n" /* <= 0: already write locked, bail */
	127	" sub %[val], %[val], 1 \n" /* counter-- */
	128	" scond %[val], [%[rwlock]] \n"
	129	" bnz 1b \n" /* retry if collided with someone */
	130	" mov %[got_it], 1 \n"
	131	" \n"
	132	"4: ; --- done --- \n"
	133
	134	: [val] "=&r" (val),
	135	[got_it] "+&r" (got_it)
	136	: [rwlock] "r" (&(rw->counter)),
	137	[WR_LOCKED] "ir" (0)
	138	: "memory", "cc");
	139
	140	smp_mb();
	141
	142	return got_it;
	143	}
	144
145	static inline void arch_write_lock(arch_rwlock_t *rw)
146	{
147	unsigned int val;
148
149	smp_mb();
150
151	/*
152	* If reader(s) hold lock (lock < __ARCH_RW_LOCK_UNLOCKED__),
153	* deny writer. Otherwise if unlocked grant to writer
154	* Hence the claim that Linux rwlocks are unfair to writers.
155	* (can be starved for an indefinite time by readers).
156	*
157	* if (rw->counter == __ARCH_RW_LOCK_UNLOCKED__) {
158	* rw->counter = 0;
159	* ret = 1;
160	* }
161	*/
162
163	__asm__ __volatile__(
164	"1: llock %[val], [%[rwlock]] \n"
165	" brne %[val], %[UNLOCKED], 1b \n" /* while !UNLOCKED spin */
166	" mov %[val], %[WR_LOCKED] \n"
167	" scond %[val], [%[rwlock]] \n"
168	" bnz 1b \n"
169	" \n"
170	: [val] "=&r" (val)
171	: [rwlock] "r" (&(rw->counter)),
172	[UNLOCKED] "ir" (__ARCH_RW_LOCK_UNLOCKED__),
173	[WR_LOCKED] "ir" (0)
174	: "memory", "cc");
175
176	smp_mb();
177	}
178
179	/* 1 - lock taken successfully */
180	static inline int arch_write_trylock(arch_rwlock_t *rw)
181	{
182	unsigned int val, got_it = 0;
183
184	smp_mb();
185
186	__asm__ __volatile__(
187	"1: llock %[val], [%[rwlock]] \n"
188	" brne %[val], %[UNLOCKED], 4f \n" /* !UNLOCKED, bail */
189	" mov %[val], %[WR_LOCKED] \n"
190	" scond %[val], [%[rwlock]] \n"
191	" bnz 1b \n" /* retry if collided with someone */
192	" mov %[got_it], 1 \n"
193	" \n"
194	"4: ; --- done --- \n"
195
196	: [val] "=&r" (val),
197	[got_it] "+&r" (got_it)
198	: [rwlock] "r" (&(rw->counter)),
199	[UNLOCKED] "ir" (__ARCH_RW_LOCK_UNLOCKED__),
200	[WR_LOCKED] "ir" (0)
201	: "memory", "cc");
202
203	smp_mb();
204
205	return got_it;
206	}
207
208	static inline void arch_read_unlock(arch_rwlock_t *rw)
209	{
210	unsigned int val;
211
212	smp_mb();
213
214	/*
215	* rw->counter++;
216	*/
217	__asm__ __volatile__(
218	"1: llock %[val], [%[rwlock]] \n"
219	" add %[val], %[val], 1 \n"
220	" scond %[val], [%[rwlock]] \n"
221	" bnz 1b \n"
222	" \n"
223	: [val] "=&r" (val)
224	: [rwlock] "r" (&(rw->counter))
225	: "memory", "cc");
226
227	smp_mb();
228	}
229
230	static inline void arch_write_unlock(arch_rwlock_t *rw)
231	{
232	smp_mb();
233
234	rw->counter = __ARCH_RW_LOCK_UNLOCKED__;
235
236	smp_mb();
237	}
238
ae7eae9e VG	239	#else /* !CONFIG_ARC_HAS_LLSC */
ae7eae9e VG	240
6e35fa2d VG	241	static inline void arch_spin_lock(arch_spinlock_t *lock)
6e35fa2d VG	242	{
ae7eae9e	243	unsigned int val = __ARCH_SPIN_LOCK_LOCKED__;
6e35fa2d	244
2576c28e VG	245	/*
	246	* This smp_mb() is technically superfluous, we only need the one
	247	* after the lock for providing the ACQUIRE semantics.
	248	* However doing the "right" thing was regressing hackbench
	249	* so keeping this, pending further investigation
	250	*/
	251	smp_mb();
	252
6e35fa2d VG	253	__asm__ __volatile__(
	254	"1: ex %0, [%1] \n"
	255	" breq %0, %2, 1b \n"
ae7eae9e	256	: "+&r" (val)
6e35fa2d VG	257	: "r"(&(lock->slock)), "ir"(__ARCH_SPIN_LOCK_LOCKED__)
6e35fa2d VG	258	: "memory");
2576c28e VG	259
	260	/*
	261	* ACQUIRE barrier to ensure load/store after taking the lock
	262	* don't "bleed-up" out of the critical section (leak-in is allowed)
	263	* http://www.spinics.net/lists/kernel/msg2010409.html
	264	*
	265	* ARCv2 only has load-load, store-store and all-all barrier
	266	* thus need the full all-all barrier
	267	*/
	268	smp_mb();
6e35fa2d VG	269	}
6e35fa2d VG	270
ae7eae9e	271	/* 1 - lock taken successfully */
6e35fa2d VG	272	static inline int arch_spin_trylock(arch_spinlock_t *lock)
6e35fa2d VG	273	{
ae7eae9e	274	unsigned int val = __ARCH_SPIN_LOCK_LOCKED__;
6e35fa2d	275
2576c28e VG	276	smp_mb();
2576c28e VG	277
6e35fa2d VG	278	__asm__ __volatile__(
6e35fa2d VG	279	"1: ex %0, [%1] \n"
ae7eae9e	280	: "+r" (val)
6e35fa2d VG	281	: "r"(&(lock->slock))
	282	: "memory");
	283
2576c28e VG	284	smp_mb();
2576c28e VG	285
ae7eae9e	286	return (val == __ARCH_SPIN_LOCK_UNLOCKED__);
6e35fa2d VG	287	}
	288
	289	static inline void arch_spin_unlock(arch_spinlock_t *lock)
	290	{
ae7eae9e	291	unsigned int val = __ARCH_SPIN_LOCK_UNLOCKED__;
6c00350b	292
2576c28e VG	293	/*
	294	* RELEASE barrier: given the instructions avail on ARCv2, full barrier
	295	* is the only option
	296	*/
	297	smp_mb();
	298
c2bdac14 VG	299	/*
	300	* EX is not really required here, a simple STore of 0 suffices.
	301	* However this causes tasklist livelocks in SystemC based SMP virtual
	302	* platforms where the systemc core scheduler uses EX as a cue for
	303	* moving to next core. Do a git log of this file for details
	304	*/
6c00350b VG	305	__asm__ __volatile__(
6c00350b VG	306	" ex %0, [%1] \n"
ae7eae9e	307	: "+r" (val)
6c00350b VG	308	: "r"(&(lock->slock))
	309	: "memory");
	310
2576c28e VG	311	/*
	312	* superfluous, but keeping for now - see pairing version in
	313	* arch_spin_lock above
	314	*/
6e35fa2d VG	315	smp_mb();
	316	}
	317
	318	/*
	319	* Read-write spinlocks, allowing multiple readers but only one writer.
69cbe630	320	* Unfair locking as Writers could be starved indefinitely by Reader(s)
6e35fa2d VG	321	*
	322	* The spinlock itself is contained in @counter and access to it is
	323	* serialized with @lock_mutex.
6e35fa2d VG	324	*/
6e35fa2d VG	325
6e35fa2d VG	326	/* 1 - lock taken successfully */
	327	static inline int arch_read_trylock(arch_rwlock_t *rw)
	328	{
	329	int ret = 0;
2a1021fc	330	unsigned long flags;
6e35fa2d	331
2a1021fc	332	local_irq_save(flags);
6e35fa2d VG	333	arch_spin_lock(&(rw->lock_mutex));
	334
	335	/*
	336	* zero means writer holds the lock exclusively, deny Reader.
	337	* Otherwise grant lock to first/subseq reader
	338	*/
	339	if (rw->counter > 0) {
	340	rw->counter--;
	341	ret = 1;
	342	}
	343
	344	arch_spin_unlock(&(rw->lock_mutex));
2a1021fc	345	local_irq_restore(flags);
6e35fa2d VG	346
	347	smp_mb();
	348	return ret;
	349	}
	350
	351	/* 1 - lock taken successfully */
	352	static inline int arch_write_trylock(arch_rwlock_t *rw)
	353	{
	354	int ret = 0;
2a1021fc	355	unsigned long flags;
6e35fa2d	356
2a1021fc	357	local_irq_save(flags);
6e35fa2d VG	358	arch_spin_lock(&(rw->lock_mutex));
	359
	360	/*
	361	* If reader(s) hold lock (lock < __ARCH_RW_LOCK_UNLOCKED__),
	362	* deny writer. Otherwise if unlocked grant to writer
	363	* Hence the claim that Linux rwlocks are unfair to writers.
	364	* (can be starved for an indefinite time by readers).
	365	*/
	366	if (rw->counter == __ARCH_RW_LOCK_UNLOCKED__) {
	367	rw->counter = 0;
	368	ret = 1;
	369	}
	370	arch_spin_unlock(&(rw->lock_mutex));
2a1021fc	371	local_irq_restore(flags);
6e35fa2d VG	372
	373	return ret;
	374	}
	375
	376	static inline void arch_read_lock(arch_rwlock_t *rw)
	377	{
	378	while (!arch_read_trylock(rw))
	379	cpu_relax();
	380	}
	381
	382	static inline void arch_write_lock(arch_rwlock_t *rw)
	383	{
	384	while (!arch_write_trylock(rw))
	385	cpu_relax();
	386	}
	387
	388	static inline void arch_read_unlock(arch_rwlock_t *rw)
	389	{
2a1021fc NC	390	unsigned long flags;
	391
	392	local_irq_save(flags);
6e35fa2d VG	393	arch_spin_lock(&(rw->lock_mutex));
	394	rw->counter++;
	395	arch_spin_unlock(&(rw->lock_mutex));
2a1021fc	396	local_irq_restore(flags);
6e35fa2d VG	397	}
	398
	399	static inline void arch_write_unlock(arch_rwlock_t *rw)
	400	{
2a1021fc NC	401	unsigned long flags;
	402
	403	local_irq_save(flags);
6e35fa2d VG	404	arch_spin_lock(&(rw->lock_mutex));
	405	rw->counter = __ARCH_RW_LOCK_UNLOCKED__;
	406	arch_spin_unlock(&(rw->lock_mutex));
2a1021fc	407	local_irq_restore(flags);
6e35fa2d VG	408	}
6e35fa2d VG	409
69cbe630 VG	410	#endif
	411
	412	#define arch_read_can_lock(x) ((x)->counter > 0)
	413	#define arch_write_can_lock(x) ((x)->counter == __ARCH_RW_LOCK_UNLOCKED__)
	414
6e35fa2d VG	415	#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
	416	#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
	417
	418	#define arch_spin_relax(lock) cpu_relax()
	419	#define arch_read_relax(lock) cpu_relax()
	420	#define arch_write_relax(lock) cpu_relax()
	421
	422	#endif /* __ASM_SPINLOCK_H */