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/bits.h>
20 #include  <linux/compiler.h>
21 #include  <linux/types.h>
22 
23 #define __HAVE_ARCH_CMPXCHG 1
24 
25 static inline unsigned long cmpxchg_u32(volatile void *ptr,
26 		unsigned long old, unsigned long new)
27 {
28 	__asm__ __volatile__(
29 		"1:	l.lwa %0, 0(%1)		\n"
30 		"	l.sfeq %0, %2		\n"
31 		"	l.bnf 2f		\n"
32 		"	 l.nop			\n"
33 		"	l.swa 0(%1), %3		\n"
34 		"	l.bnf 1b		\n"
35 		"	 l.nop			\n"
36 		"2:				\n"
37 		: "=&r"(old)
38 		: "r"(ptr), "r"(old), "r"(new)
39 		: "cc", "memory");
40 
41 	return old;
42 }
43 
44 static inline unsigned long xchg_u32(volatile void *ptr,
45 		unsigned long val)
46 {
47 	__asm__ __volatile__(
48 		"1:	l.lwa %0, 0(%1)		\n"
49 		"	l.swa 0(%1), %2		\n"
50 		"	l.bnf 1b		\n"
51 		"	 l.nop			\n"
52 		: "=&r"(val)
53 		: "r"(ptr), "r"(val)
54 		: "cc", "memory");
55 
56 	return val;
57 }
58 
59 static inline u32 cmpxchg_small(volatile void *ptr, u32 old, u32 new,
60 				int size)
61 {
62 	int off = (unsigned long)ptr % sizeof(u32);
63 	volatile u32 *p = ptr - off;
64 #ifdef __BIG_ENDIAN
65 	int bitoff = (sizeof(u32) - size - off) * BITS_PER_BYTE;
66 #else
67 	int bitoff = off * BITS_PER_BYTE;
68 #endif
69 	u32 bitmask = ((0x1 << size * BITS_PER_BYTE) - 1) << bitoff;
70 	u32 load32, old32, new32;
71 	u32 ret;
72 
73 	load32 = READ_ONCE(*p);
74 
75 	while (true) {
76 		ret = (load32 & bitmask) >> bitoff;
77 		if (old != ret)
78 			return ret;
79 
80 		old32 = (load32 & ~bitmask) | (old << bitoff);
81 		new32 = (load32 & ~bitmask) | (new << bitoff);
82 
83 		/* Do 32 bit cmpxchg */
84 		load32 = cmpxchg_u32(p, old32, new32);
85 		if (load32 == old32)
86 			return old;
87 	}
88 }
89 
90 /* xchg */
91 
92 static inline u32 xchg_small(volatile void *ptr, u32 x, int size)
93 {
94 	int off = (unsigned long)ptr % sizeof(u32);
95 	volatile u32 *p = ptr - off;
96 #ifdef __BIG_ENDIAN
97 	int bitoff = (sizeof(u32) - size - off) * BITS_PER_BYTE;
98 #else
99 	int bitoff = off * BITS_PER_BYTE;
100 #endif
101 	u32 bitmask = ((0x1 << size * BITS_PER_BYTE) - 1) << bitoff;
102 	u32 oldv, newv;
103 	u32 ret;
104 
105 	do {
106 		oldv = READ_ONCE(*p);
107 		ret = (oldv & bitmask) >> bitoff;
108 		newv = (oldv & ~bitmask) | (x << bitoff);
109 	} while (cmpxchg_u32(p, oldv, newv) != oldv);
110 
111 	return ret;
112 }
113 
114 /*
115  * This function doesn't exist, so you'll get a linker error
116  * if something tries to do an invalid cmpxchg().
117  */
118 extern unsigned long __cmpxchg_called_with_bad_pointer(void)
119 	__compiletime_error("Bad argument size for cmpxchg");
120 
121 static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
122 		unsigned long new, int size)
123 {
124 	switch (size) {
125 	case 1:
126 	case 2:
127 		return cmpxchg_small(ptr, old, new, size);
128 	case 4:
129 		return cmpxchg_u32(ptr, old, new);
130 	default:
131 		return __cmpxchg_called_with_bad_pointer();
132 	}
133 }
134 
135 #define cmpxchg(ptr, o, n)						\
136 	({								\
137 		(__typeof__(*(ptr))) __cmpxchg((ptr),			\
138 					       (unsigned long)(o),	\
139 					       (unsigned long)(n),	\
140 					       sizeof(*(ptr)));		\
141 	})
142 
143 /*
144  * This function doesn't exist, so you'll get a linker error if
145  * something tries to do an invalidly-sized xchg().
146  */
147 extern unsigned long __xchg_called_with_bad_pointer(void)
148 	__compiletime_error("Bad argument size for xchg");
149 
150 static inline unsigned long __xchg(volatile void *ptr, unsigned long with,
151 		int size)
152 {
153 	switch (size) {
154 	case 1:
155 	case 2:
156 		return xchg_small(ptr, with, size);
157 	case 4:
158 		return xchg_u32(ptr, with);
159 	default:
160 		return __xchg_called_with_bad_pointer();
161 	}
162 }
163 
164 #define xchg(ptr, with) 						\
165 	({								\
166 		(__typeof__(*(ptr))) __xchg((ptr),			\
167 					    (unsigned long)(with),	\
168 					    sizeof(*(ptr)));		\
169 	})
170 
171 #endif /* __ASM_OPENRISC_CMPXCHG_H */
172