1 /*
2  * Spin and read/write lock operations.
3  *
4  * Copyright (C) 2001-2004 Paul Mackerras <paulus@au.ibm.com>, IBM
5  * Copyright (C) 2001 Anton Blanchard <anton@au.ibm.com>, IBM
6  * Copyright (C) 2002 Dave Engebretsen <engebret@us.ibm.com>, IBM
7  *   Rework to support virtual processors
8  *
9  * This program is free software; you can redistribute it and/or
10  * modify it under the terms of the GNU General Public License
11  * as published by the Free Software Foundation; either version
12  * 2 of the License, or (at your option) any later version.
13  */
14 
15 #include <linux/kernel.h>
16 #include <linux/spinlock.h>
17 #include <linux/export.h>
18 #include <linux/stringify.h>
19 #include <linux/smp.h>
20 
21 /* waiting for a spinlock... */
22 #if defined(CONFIG_PPC_SPLPAR)
23 #include <asm/hvcall.h>
24 #include <asm/smp.h>
25 
__spin_yield(arch_spinlock_t * lock)26 void __spin_yield(arch_spinlock_t *lock)
27 {
28 	unsigned int lock_value, holder_cpu, yield_count;
29 
30 	lock_value = lock->slock;
31 	if (lock_value == 0)
32 		return;
33 	holder_cpu = lock_value & 0xffff;
34 	BUG_ON(holder_cpu >= NR_CPUS);
35 	yield_count = lppaca_of(holder_cpu).yield_count;
36 	if ((yield_count & 1) == 0)
37 		return;		/* virtual cpu is currently running */
38 	rmb();
39 	if (lock->slock != lock_value)
40 		return;		/* something has changed */
41 	plpar_hcall_norets(H_CONFER,
42 		get_hard_smp_processor_id(holder_cpu), yield_count);
43 }
44 
45 /*
46  * Waiting for a read lock or a write lock on a rwlock...
47  * This turns out to be the same for read and write locks, since
48  * we only know the holder if it is write-locked.
49  */
__rw_yield(arch_rwlock_t * rw)50 void __rw_yield(arch_rwlock_t *rw)
51 {
52 	int lock_value;
53 	unsigned int holder_cpu, yield_count;
54 
55 	lock_value = rw->lock;
56 	if (lock_value >= 0)
57 		return;		/* no write lock at present */
58 	holder_cpu = lock_value & 0xffff;
59 	BUG_ON(holder_cpu >= NR_CPUS);
60 	yield_count = lppaca_of(holder_cpu).yield_count;
61 	if ((yield_count & 1) == 0)
62 		return;		/* virtual cpu is currently running */
63 	rmb();
64 	if (rw->lock != lock_value)
65 		return;		/* something has changed */
66 	plpar_hcall_norets(H_CONFER,
67 		get_hard_smp_processor_id(holder_cpu), yield_count);
68 }
69 #endif
70 
arch_spin_unlock_wait(arch_spinlock_t * lock)71 void arch_spin_unlock_wait(arch_spinlock_t *lock)
72 {
73 	while (lock->slock) {
74 		HMT_low();
75 		if (SHARED_PROCESSOR)
76 			__spin_yield(lock);
77 	}
78 	HMT_medium();
79 }
80 
81 EXPORT_SYMBOL(arch_spin_unlock_wait);
82