cmpxchg.h

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/*
 * xchg/cmpxchg operations for the Hexagon architecture
 *
 * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.
 *
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 and
 * only version 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */

#ifndef _ASM_CMPXCHG_H
#define _ASM_CMPXCHG_H

/*
 * __xchg - atomically exchange a register and a memory location
 * @x: value to swap
 * @ptr: pointer to memory
 * @size:  size of the value
 *
 * Only 4 bytes supported currently.
 *
 * Note:  there was an errata for V2 about .new's and memw_locked.
 *
 */
static inline unsigned long __xchg(unsigned long x, volatile void *ptr,
                   int size)
{
    unsigned long retval;

    /*  Can't seem to use printk or panic here, so just stop  */
    if (size != 4) do { asm volatile("brkpt;\n"); } while (1);

    __asm__ __volatile__ (
    "1: %0 = memw_locked(%1);\n"    /*  load into retval */
    "   memw_locked(%1,P0) = %2;\n" /*  store into memory */
    "   if !P0 jump 1b;\n"
    : "=&r" (retval)
    : "r" (ptr), "r" (x)
    : "memory", "p0"
    );
    return retval;
}

/*
 * Atomically swap the contents of a register with memory.  Should be atomic
 * between multiple CPU's and within interrupts on the same CPU.
 */
#define xchg(ptr, v) ((__typeof__(*(ptr)))__xchg((unsigned long)(v), (ptr), \
    sizeof(*(ptr))))

/*
 *  see rt-mutex-design.txt; cmpxchg supposedly checks if *ptr == A and swaps.
 *  looks just like atomic_cmpxchg on our arch currently with a bunch of
 *  variable casting.
 */
#define __HAVE_ARCH_CMPXCHG 1

#define cmpxchg(ptr, old, new)                  \
({                              \
    __typeof__(ptr) __ptr = (ptr);              \
    __typeof__(*(ptr)) __old = (old);           \
    __typeof__(*(ptr)) __new = (new);           \
    __typeof__(*(ptr)) __oldval = 0;            \
                                \
    asm volatile(                       \
        "1: %0 = memw_locked(%1);\n"        \
        "   { P0 = cmp.eq(%0,%2);\n"        \
        "     if (!P0.new) jump:nt 2f; }\n"     \
        "   memw_locked(%1,p0) = %3;\n"     \
        "   if (!P0) jump 1b;\n"            \
        "2:\n"                      \
        : "=&r" (__oldval)              \
        : "r" (__ptr), "r" (__old), "r" (__new)     \
        : "memory", "p0"                \
    );                          \
    __oldval;                       \
})

#endif /* _ASM_CMPXCHG_H */