1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Copyright (C) 2017 Imagination Technologies
4 * Author: Paul Burton <paul.burton@mips.com>
5 */
6
7#include <linux/bitops.h>
8#include <asm/cmpxchg.h>
9
10unsigned long __xchg_small(volatile void *ptr, unsigned long val, unsigned int size)
11{
12	u32 old32, new32, load32, mask;
13	volatile u32 *ptr32;
14	unsigned int shift;
15
16	/* Check that ptr is naturally aligned */
17	WARN_ON((unsigned long)ptr & (size - 1));
18
19	/* Mask value to the correct size. */
20	mask = GENMASK((size * BITS_PER_BYTE) - 1, 0);
21	val &= mask;
22
23	/*
24	 * Calculate a shift & mask that correspond to the value we wish to
25	 * exchange within the naturally aligned 4 byte integer that includes
26	 * it.
27	 */
28	shift = (unsigned long)ptr & 0x3;
29	if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
30		shift ^= sizeof(u32) - size;
31	shift *= BITS_PER_BYTE;
32	mask <<= shift;
33
34	/*
35	 * Calculate a pointer to the naturally aligned 4 byte integer that
36	 * includes our byte of interest, and load its value.
37	 */
38	ptr32 = (volatile u32 *)((unsigned long)ptr & ~0x3);
39	load32 = *ptr32;
40
41	do {
42		old32 = load32;
43		new32 = (load32 & ~mask) | (val << shift);
44		load32 = arch_cmpxchg(ptr32, old32, new32);
45	} while (load32 != old32);
46
47	return (load32 & mask) >> shift;
48}
49
50unsigned long __cmpxchg_small(volatile void *ptr, unsigned long old,
51			      unsigned long new, unsigned int size)
52{
53	u32 mask, old32, new32, load32, load;
54	volatile u32 *ptr32;
55	unsigned int shift;
56
57	/* Check that ptr is naturally aligned */
58	WARN_ON((unsigned long)ptr & (size - 1));
59
60	/* Mask inputs to the correct size. */
61	mask = GENMASK((size * BITS_PER_BYTE) - 1, 0);
62	old &= mask;
63	new &= mask;
64
65	/*
66	 * Calculate a shift & mask that correspond to the value we wish to
67	 * compare & exchange within the naturally aligned 4 byte integer
68	 * that includes it.
69	 */
70	shift = (unsigned long)ptr & 0x3;
71	if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
72		shift ^= sizeof(u32) - size;
73	shift *= BITS_PER_BYTE;
74	mask <<= shift;
75
76	/*
77	 * Calculate a pointer to the naturally aligned 4 byte integer that
78	 * includes our byte of interest, and load its value.
79	 */
80	ptr32 = (volatile u32 *)((unsigned long)ptr & ~0x3);
81	load32 = *ptr32;
82
83	while (true) {
84		/*
85		 * Ensure the byte we want to exchange matches the expected
86		 * old value, and if not then bail.
87		 */
88		load = (load32 & mask) >> shift;
89		if (load != old)
90			return load;
91
92		/*
93		 * Calculate the old & new values of the naturally aligned
94		 * 4 byte integer that include the byte we want to exchange.
95		 * Attempt to exchange the old value for the new value, and
96		 * return if we succeed.
97		 */
98		old32 = (load32 & ~mask) | (old << shift);
99		new32 = (load32 & ~mask) | (new << shift);
100		load32 = arch_cmpxchg(ptr32, old32, new32);
101		if (load32 == old32)
102			return old;
103	}
104}
105