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/*
* Copyright (C) 2017 Imagination Technologies
* Author: Paul Burton <paul.burton@imgtec.com>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* option) any later version.
*/
#include <linux/bitops.h>
#include <asm/cmpxchg.h>
unsigned long __xchg_small(volatile void *ptr, unsigned long val, unsigned int size)
{
u32 old32, new32, load32, mask;
volatile u32 *ptr32;
unsigned int shift;
/* Check that ptr is naturally aligned */
WARN_ON((unsigned long)ptr & (size - 1));
/* Mask value to the correct size. */
mask = GENMASK((size * BITS_PER_BYTE) - 1, 0);
val &= mask;
/*
* Calculate a shift & mask that correspond to the value we wish to
* exchange within the naturally aligned 4 byte integerthat includes
* it.
*/
shift = (unsigned long)ptr & 0x3;
if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
shift ^= sizeof(u32) - size;
shift *= BITS_PER_BYTE;
mask <<= shift;
/*
* Calculate a pointer to the naturally aligned 4 byte integer that
* includes our byte of interest, and load its value.
*/
ptr32 = (volatile u32 *)((unsigned long)ptr & ~0x3);
load32 = *ptr32;
do {
old32 = load32;
new32 = (load32 & ~mask) | (val << shift);
load32 = cmpxchg(ptr32, old32, new32);
} while (load32 != old32);
return (load32 & mask) >> shift;
}
unsigned long __cmpxchg_small(volatile void *ptr, unsigned long old,
unsigned long new, unsigned int size)
{
u32 mask, old32, new32, load32;
volatile u32 *ptr32;
unsigned int shift;
u8 load;
/* Check that ptr is naturally aligned */
WARN_ON((unsigned long)ptr & (size - 1));
/* Mask inputs to the correct size. */
mask = GENMASK((size * BITS_PER_BYTE) - 1, 0);
old &= mask;
new &= mask;
/*
* Calculate a shift & mask that correspond to the value we wish to
* compare & exchange within the naturally aligned 4 byte integer
* that includes it.
*/
shift = (unsigned long)ptr & 0x3;
if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
shift ^= sizeof(u32) - size;
shift *= BITS_PER_BYTE;
mask <<= shift;
/*
* Calculate a pointer to the naturally aligned 4 byte integer that
* includes our byte of interest, and load its value.
*/
ptr32 = (volatile u32 *)((unsigned long)ptr & ~0x3);
load32 = *ptr32;
while (true) {
/*
* Ensure the byte we want to exchange matches the expected
* old value, and if not then bail.
*/
load = (load32 & mask) >> shift;
if (load != old)
return load;
/*
* Calculate the old & new values of the naturally aligned
* 4 byte integer that include the byte we want to exchange.
* Attempt to exchange the old value for the new value, and
* return if we succeed.
*/
old32 = (load32 & ~mask) | (old << shift);
new32 = (load32 & ~mask) | (new << shift);
load32 = cmpxchg(ptr32, old32, new32);
if (load32 == old32)
return old;
}
}
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