linux/arch/powerpc/lib/locks.c
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   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
  26void __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 */
  50void __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
  71void 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
  81EXPORT_SYMBOL(arch_spin_unlock_wait);
  82