1 /*
2 * Copyright (C) 2017 Imagination Technologies
3 * Author: Paul Burton <paul.burton@mips.com>
4 *
5 * This program is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License as published by the
7 * Free Software Foundation; either version 2 of the License, or (at your
8 * option) any later version.
9 */
10
11 #include <linux/bitops.h>
12 #include <asm/cmpxchg.h>
13
__xchg_small(volatile void * ptr,unsigned long val,unsigned int size)14 unsigned long __xchg_small(volatile void *ptr, unsigned long val, unsigned int size)
15 {
16 u32 old32, new32, load32, mask;
17 volatile u32 *ptr32;
18 unsigned int shift;
19
20 /* Check that ptr is naturally aligned */
21 WARN_ON((unsigned long)ptr & (size - 1));
22
23 /* Mask value to the correct size. */
24 mask = GENMASK((size * BITS_PER_BYTE) - 1, 0);
25 val &= mask;
26
27 /*
28 * Calculate a shift & mask that correspond to the value we wish to
29 * exchange within the naturally aligned 4 byte integerthat includes
30 * it.
31 */
32 shift = (unsigned long)ptr & 0x3;
33 if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
34 shift ^= sizeof(u32) - size;
35 shift *= BITS_PER_BYTE;
36 mask <<= shift;
37
38 /*
39 * Calculate a pointer to the naturally aligned 4 byte integer that
40 * includes our byte of interest, and load its value.
41 */
42 ptr32 = (volatile u32 *)((unsigned long)ptr & ~0x3);
43 load32 = *ptr32;
44
45 do {
46 old32 = load32;
47 new32 = (load32 & ~mask) | (val << shift);
48 load32 = cmpxchg(ptr32, old32, new32);
49 } while (load32 != old32);
50
51 return (load32 & mask) >> shift;
52 }
53
__cmpxchg_small(volatile void * ptr,unsigned long old,unsigned long new,unsigned int size)54 unsigned long __cmpxchg_small(volatile void *ptr, unsigned long old,
55 unsigned long new, unsigned int size)
56 {
57 u32 mask, old32, new32, load32;
58 volatile u32 *ptr32;
59 unsigned int shift;
60 u8 load;
61
62 /* Check that ptr is naturally aligned */
63 WARN_ON((unsigned long)ptr & (size - 1));
64
65 /* Mask inputs to the correct size. */
66 mask = GENMASK((size * BITS_PER_BYTE) - 1, 0);
67 old &= mask;
68 new &= mask;
69
70 /*
71 * Calculate a shift & mask that correspond to the value we wish to
72 * compare & exchange within the naturally aligned 4 byte integer
73 * that includes it.
74 */
75 shift = (unsigned long)ptr & 0x3;
76 if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
77 shift ^= sizeof(u32) - size;
78 shift *= BITS_PER_BYTE;
79 mask <<= shift;
80
81 /*
82 * Calculate a pointer to the naturally aligned 4 byte integer that
83 * includes our byte of interest, and load its value.
84 */
85 ptr32 = (volatile u32 *)((unsigned long)ptr & ~0x3);
86 load32 = *ptr32;
87
88 while (true) {
89 /*
90 * Ensure the byte we want to exchange matches the expected
91 * old value, and if not then bail.
92 */
93 load = (load32 & mask) >> shift;
94 if (load != old)
95 return load;
96
97 /*
98 * Calculate the old & new values of the naturally aligned
99 * 4 byte integer that include the byte we want to exchange.
100 * Attempt to exchange the old value for the new value, and
101 * return if we succeed.
102 */
103 old32 = (load32 & ~mask) | (old << shift);
104 new32 = (load32 & ~mask) | (new << shift);
105 load32 = cmpxchg(ptr32, old32, new32);
106 if (load32 == old32)
107 return old;
108 }
109 }
110
