1 /*
2  * 1,2 and 4 byte cmpxchg and xchg implementations for OpenRISC.
3  *
4  * Copyright (C) 2014 Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
5  * Copyright (C) 2017 Stafford Horne <shorne@gmail.com>
6  *
7  * This file is licensed under the terms of the GNU General Public License
8  * version 2.  This program is licensed "as is" without any warranty of any
9  * kind, whether express or implied.
10  *
11  * Note:
12  * The portable implementations of 1 and 2 byte xchg and cmpxchg using a 4
13  * byte cmpxchg is sourced heavily from the sh and mips implementations.
14  */
15 
16 #ifndef __ASM_OPENRISC_CMPXCHG_H
17 #define __ASM_OPENRISC_CMPXCHG_H
18 
19 #include  <linux/types.h>
20 #include  <linux/bitops.h>
21 
22 #define __HAVE_ARCH_CMPXCHG 1
23 
24 static inline unsigned long cmpxchg_u32(volatile void *ptr,
25 		unsigned long old, unsigned long new)
26 {
27 	__asm__ __volatile__(
28 		"1:	l.lwa %0, 0(%1)		\n"
29 		"	l.sfeq %0, %2		\n"
30 		"	l.bnf 2f		\n"
31 		"	 l.nop			\n"
32 		"	l.swa 0(%1), %3		\n"
33 		"	l.bnf 1b		\n"
34 		"	 l.nop			\n"
35 		"2:				\n"
36 		: "=&r"(old)
37 		: "r"(ptr), "r"(old), "r"(new)
38 		: "cc", "memory");
39 
40 	return old;
41 }
42 
43 static inline unsigned long xchg_u32(volatile void *ptr,
44 		unsigned long val)
45 {
46 	__asm__ __volatile__(
47 		"1:	l.lwa %0, 0(%1)		\n"
48 		"	l.swa 0(%1), %2		\n"
49 		"	l.bnf 1b		\n"
50 		"	 l.nop			\n"
51 		: "=&r"(val)
52 		: "r"(ptr), "r"(val)
53 		: "cc", "memory");
54 
55 	return val;
56 }
57 
58 static inline u32 cmpxchg_small(volatile void *ptr, u32 old, u32 new,
59 				int size)
60 {
61 	int off = (unsigned long)ptr % sizeof(u32);
62 	volatile u32 *p = ptr - off;
63 #ifdef __BIG_ENDIAN
64 	int bitoff = (sizeof(u32) - size - off) * BITS_PER_BYTE;
65 #else
66 	int bitoff = off * BITS_PER_BYTE;
67 #endif
68 	u32 bitmask = ((0x1 << size * BITS_PER_BYTE) - 1) << bitoff;
69 	u32 load32, old32, new32;
70 	u32 ret;
71 
72 	load32 = READ_ONCE(*p);
73 
74 	while (true) {
75 		ret = (load32 & bitmask) >> bitoff;
76 		if (old != ret)
77 			return ret;
78 
79 		old32 = (load32 & ~bitmask) | (old << bitoff);
80 		new32 = (load32 & ~bitmask) | (new << bitoff);
81 
82 		/* Do 32 bit cmpxchg */
83 		load32 = cmpxchg_u32(p, old32, new32);
84 		if (load32 == old32)
85 			return old;
86 	}
87 }
88 
89 /* xchg */
90 
91 static inline u32 xchg_small(volatile void *ptr, u32 x, int size)
92 {
93 	int off = (unsigned long)ptr % sizeof(u32);
94 	volatile u32 *p = ptr - off;
95 #ifdef __BIG_ENDIAN
96 	int bitoff = (sizeof(u32) - size - off) * BITS_PER_BYTE;
97 #else
98 	int bitoff = off * BITS_PER_BYTE;
99 #endif
100 	u32 bitmask = ((0x1 << size * BITS_PER_BYTE) - 1) << bitoff;
101 	u32 oldv, newv;
102 	u32 ret;
103 
104 	do {
105 		oldv = READ_ONCE(*p);
106 		ret = (oldv & bitmask) >> bitoff;
107 		newv = (oldv & ~bitmask) | (x << bitoff);
108 	} while (cmpxchg_u32(p, oldv, newv) != oldv);
109 
110 	return ret;
111 }
112 
113 /*
114  * This function doesn't exist, so you'll get a linker error
115  * if something tries to do an invalid cmpxchg().
116  */
117 extern unsigned long __cmpxchg_called_with_bad_pointer(void)
118 	__compiletime_error("Bad argument size for cmpxchg");
119 
120 static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
121 		unsigned long new, int size)
122 {
123 	switch (size) {
124 	case 1:
125 	case 2:
126 		return cmpxchg_small(ptr, old, new, size);
127 	case 4:
128 		return cmpxchg_u32(ptr, old, new);
129 	default:
130 		return __cmpxchg_called_with_bad_pointer();
131 	}
132 }
133 
134 #define cmpxchg(ptr, o, n)						\
135 	({								\
136 		(__typeof__(*(ptr))) __cmpxchg((ptr),			\
137 					       (unsigned long)(o),	\
138 					       (unsigned long)(n),	\
139 					       sizeof(*(ptr)));		\
140 	})
141 
142 /*
143  * This function doesn't exist, so you'll get a linker error if
144  * something tries to do an invalidly-sized xchg().
145  */
146 extern unsigned long __xchg_called_with_bad_pointer(void)
147 	__compiletime_error("Bad argument size for xchg");
148 
149 static inline unsigned long __xchg(volatile void *ptr, unsigned long with,
150 		int size)
151 {
152 	switch (size) {
153 	case 1:
154 	case 2:
155 		return xchg_small(ptr, with, size);
156 	case 4:
157 		return xchg_u32(ptr, with);
158 	default:
159 		return __xchg_called_with_bad_pointer();
160 	}
161 }
162 
163 #define xchg(ptr, with) 						\
164 	({								\
165 		(__typeof__(*(ptr))) __xchg((ptr),			\
166 					    (unsigned long)(with),	\
167 					    sizeof(*(ptr)));		\
168 	})
169 
170 #endif /* __ASM_OPENRISC_CMPXCHG_H */
171