LXR linux/arch/powerpc/lib/locks.c

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 * Spin and read/write lock operations.
   4 *
   5 * Copyright (C) 2001-2004 Paul Mackerras <paulus@au.ibm.com>, IBM
   6 * Copyright (C) 2001 Anton Blanchard <anton@au.ibm.com>, IBM
   7 * Copyright (C) 2002 Dave Engebretsen <engebret@us.ibm.com>, IBM
   8 *   Rework to support virtual processors
   9 */
  10
  11#include <linux/kernel.h>
  12#include <linux/spinlock.h>
  13#include <linux/export.h>
  14#include <linux/smp.h>
  15
  16/* waiting for a spinlock... */
  17#if defined(CONFIG_PPC_SPLPAR)
  18#include <asm/hvcall.h>
  19#include <asm/smp.h>
  20
  21void splpar_spin_yield(arch_spinlock_t *lock)
  22{
  23        unsigned int lock_value, holder_cpu, yield_count;
  24
  25        lock_value = lock->slock;
  26        if (lock_value == 0)
  27                return;
  28        holder_cpu = lock_value & 0xffff;
  29        BUG_ON(holder_cpu >= NR_CPUS);
  30
  31        yield_count = yield_count_of(holder_cpu);
  32        if ((yield_count & 1) == 0)
  33                return;         /* virtual cpu is currently running */
  34        rmb();
  35        if (lock->slock != lock_value)
  36                return;         /* something has changed */
  37        yield_to_preempted(holder_cpu, yield_count);
  38}
  39EXPORT_SYMBOL_GPL(splpar_spin_yield);
  40
  41/*
  42 * Waiting for a read lock or a write lock on a rwlock...
  43 * This turns out to be the same for read and write locks, since
  44 * we only know the holder if it is write-locked.
  45 */
  46void splpar_rw_yield(arch_rwlock_t *rw)
  47{
  48        int lock_value;
  49        unsigned int holder_cpu, yield_count;
  50
  51        lock_value = rw->lock;
  52        if (lock_value >= 0)
  53                return;         /* no write lock at present */
  54        holder_cpu = lock_value & 0xffff;
  55        BUG_ON(holder_cpu >= NR_CPUS);
  56
  57        yield_count = yield_count_of(holder_cpu);
  58        if ((yield_count & 1) == 0)
  59                return;         /* virtual cpu is currently running */
  60        rmb();
  61        if (rw->lock != lock_value)
  62                return;         /* something has changed */
  63        yield_to_preempted(holder_cpu, yield_count);
  64}
  65#endif
  66