arch/powerpc/lib/locks.c

   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
  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 = be32_to_cpu(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 EXPORT_SYMBOL_GPL(__spin_yield);
  45
  46 /*
  47  * Waiting for a read lock or a write lock on a rwlock...
  48  * This turns out to be the same for read and write locks, since
  49  * we only know the holder if it is write-locked.
  50  */
  51 void __rw_yield(arch_rwlock_t *rw)
  52 {
  53         int lock_value;
  54         unsigned int holder_cpu, yield_count;
  55
  56         lock_value = rw->lock;
  57         if (lock_value >= 0)
  58                 return;         /* no write lock at present */
  59         holder_cpu = lock_value & 0xffff;
  60         BUG_ON(holder_cpu >= NR_CPUS);
  61         yield_count = be32_to_cpu(lppaca_of(holder_cpu).yield_count);
  62         if ((yield_count & 1) == 0)
  63                 return;         /* virtual cpu is currently running */
  64         rmb();
  65         if (rw->lock != lock_value)
  66                 return;         /* something has changed */
  67         plpar_hcall_norets(H_CONFER,
  68                 get_hard_smp_processor_id(holder_cpu), yield_count);
  69 }
  70 #endif
  71
  72 void arch_spin_unlock_wait(arch_spinlock_t *lock)
  73 {
  74         smp_mb();
  75
  76         while (lock->slock) {
  77                 HMT_low();
  78                 if (SHARED_PROCESSOR)
  79                         __spin_yield(lock);
  80         }
  81         HMT_medium();
  82
  83         smp_mb();
  84 }
  85
  86 EXPORT_SYMBOL(arch_spin_unlock_wait);